Remove a great many cases where mgrd is accessed directly in favour

of monster_at().
The hope is to eventually remove mgrd completely (in favour of scanning
through the monster list, or a different datastructure which gets updated
automatically when monsters move), and thus fix all the mgrd-out-of-sync
bugs in one fell swoop.


git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@9056 c06c8d41-db1a-0410-9941-cceddc491573

24 files changed, 336 insertions, 451 deletions

diff --git a/crawl-ref/source/abl-show.cc b/crawl-ref/source/abl-show.cc
index 927eb987ed..dc3bee5714 100644
--- a/crawl-ref/source/abl-show.cc
+++ b/crawl-ref/source/abl-show.cc
@@ -2418,32 +2418,34 @@ static int _find_ability_slot( ability_type which_ability )
 
 static int _lugonu_warp_monster(coord_def where, int pow, int, actor *)
 {
-    if (!in_bounds(where) || mgrd(where) == NON_MONSTER)
+    if (!in_bounds(where))
         return (0);
 
-    monsters &mon = menv[ mgrd(where) ];
+    monsters* mon = monster_at(where);
+    if (mon == NULL)
+        return (0);
 
-    if (!mons_friendly(&mon))
-        behaviour_event( &mon, ME_ANNOY, MHITYOU );
+    if (!mons_friendly(mon))
+        behaviour_event(mon, ME_ANNOY, MHITYOU);
 
-    if (check_mons_resist_magic(&mon, pow * 2))
+    if (check_mons_resist_magic(mon, pow * 2))
     {
         mprf("%s %s.",
-             mon.name(DESC_CAP_THE).c_str(), mons_resist_string(&mon));
+             mon->name(DESC_CAP_THE).c_str(), mons_resist_string(mon));
         return (1);
     }
 
     const int damage = 1 + random2(pow / 6);
-    if (mon.type == MONS_BLINK_FROG)
-        mon.heal(damage, false);
-    else if (!check_mons_resist_magic(&mon, pow))
+    if (mon->type == MONS_BLINK_FROG)
+        mon->heal(damage, false);
+    else if (!check_mons_resist_magic(mon, pow))
     {
-        mon.hurt(&you, damage);
-        if (!mon.alive())
+        mon->hurt(&you, damage);
+        if (!mon->alive())
             return (1);
     }
 
-    mon.blink();
+    mon->blink();
 
     return (1);
 }
diff --git a/crawl-ref/source/abyss.cc b/crawl-ref/source/abyss.cc
index 352caeb7e2..b5eaa2ecbb 100644
--- a/crawl-ref/source/abyss.cc
+++ b/crawl-ref/source/abyss.cc
@@ -21,6 +21,7 @@ REVISION("$Rev$");
 #include "mapmark.h"
 #include "message.h"
 #include "misc.h"
+#include "mon-util.h"
 #include "monplace.h"
 #include "mtransit.h"
 #include "player.h"
@@ -467,8 +468,8 @@ void area_shift(void)
 #endif
         lose_item_stack( *ri );
 
-        if (mgrd(*ri) != NON_MONSTER)
-            _abyss_lose_monster( menv[ mgrd(*ri) ] );
+        if (monsters* m = monster_at(*ri))
+            _abyss_lose_monster(*m);
     }
 
     // Shift all monsters and items to new area.
diff --git a/crawl-ref/source/acr.cc b/crawl-ref/source/acr.cc
index 4777fde84a..79d4b72cba 100644
--- a/crawl-ref/source/acr.cc
+++ b/crawl-ref/source/acr.cc
@@ -2960,26 +2960,26 @@ static void _open_door(coord_def move, bool check_confused)
     {
         doorpos = you.pos() + move;
 
-        const int mon = mgrd(doorpos);
+        monsters* mon = monster_at(doorpos);
 
-        if (mon != NON_MONSTER && player_can_hit_monster(&menv[mon]))
+        if (mon && player_can_hit_monster(mon))
         {
-            if (mons_is_caught(&menv[mon]))
+            if (mons_is_caught(mon))
             {
-                std::string prompt  = "Do you want to try to take the net off ";
-                            prompt += (&menv[mon])->name(DESC_NOCAP_THE);
-                            prompt += '?';
+                const std::string prompt =
+                    make_stringf("Do you want to try to take the net off %s?",
+                                 mon->name(DESC_NOCAP_THE).c_str());
 
                 if (yesno(prompt.c_str(), true, 'n'))
                 {
-                    remove_net_from(&menv[mon]);
+                    remove_net_from(mon);
                     return;
                 }
 
             }
 
             you.turn_is_over = true;
-            you_attack(mgrd(doorpos), true);
+            you_attack(mon->mindex(), true);
 
             if (you.berserk_penalty != NO_BERSERK_PENALTY)
                 you.berserk_penalty = 0;
@@ -3172,11 +3172,11 @@ static void _close_door(coord_def move)
              i != all_door.end(); ++i)
         {
             const coord_def& dc = *i;
-            if (mgrd(dc) != NON_MONSTER)
+            if (monsters* mon = monster_at(dc))
             {
                 // Need to make sure that turn_is_over is set if creature is
                 // invisible.
-                if (!player_monster_visible(&menv[mgrd(dc)]))
+                if (!player_monster_visible(mon))
                 {
                     mprf("Something is blocking the %sway!", noun);
                     you.turn_is_over = true;
@@ -3575,14 +3575,14 @@ static void _move_player(coord_def move)
 
     const coord_def& targ = you.pos() + move;
     const dungeon_feature_type targ_grid  =  grd(targ);
-    const unsigned short targ_monst = mgrd(targ);
+          monsters*      targ_monst = monster_at(targ);
     const bool           targ_pass  = you.can_pass_through(targ);
 
     // You can swap places with a friendly or good neutral monster if
     // you're not confused, or if both of you are inside a sanctuary.
-    const bool can_swap_places = targ_monst != NON_MONSTER
-                                 && !mons_is_stationary(&menv[targ_monst])
-                                 && (mons_wont_attack(&menv[targ_monst])
+    const bool can_swap_places = targ_monst
+                                 && !mons_is_stationary(targ_monst)
+                                 && (mons_wont_attack(targ_monst)
                                        && !you.confused()
                                      || is_sanctuary(you.pos())
                                         && is_sanctuary(targ));
@@ -3615,13 +3615,11 @@ static void _move_player(coord_def move)
 
     coord_def mon_swap_dest;
 
-    if (targ_monst != NON_MONSTER && !mons_is_submerged(&menv[targ_monst]))
+    if (targ_monst && !mons_is_submerged(targ_monst))
     {
-        monsters *mon = &menv[targ_monst];
-
         if (can_swap_places && !beholder)
         {
-            if (swap_check(mon, mon_swap_dest))
+            if (swap_check(targ_monst, mon_swap_dest))
                 swap = true;
             else
                 moving = false;
@@ -3634,7 +3632,7 @@ static void _move_player(coord_def move)
             // the player to figure out which adjacent wall an invis
             // monster is in "for free".
             you.turn_is_over = true;
-            you_attack( targ_monst, true );
+            you_attack(targ_monst->mindex(), true);
 
             // We don't want to create a penalty if there isn't
             // supposed to be one.
@@ -3653,7 +3651,7 @@ static void _move_player(coord_def move)
             return;
 
         if (swap)
-            swap_places(&menv[targ_monst], mon_swap_dest);
+            swap_places(targ_monst, mon_swap_dest);
 
         you.prev_move = move;
         move.reset();
diff --git a/crawl-ref/source/beam.cc b/crawl-ref/source/beam.cc
index adc278cc61..c8238fbe86 100644
--- a/crawl-ref/source/beam.cc
+++ b/crawl-ref/source/beam.cc
@@ -1504,13 +1504,13 @@ void bolt::initialize_fire()
     if (!seen && see_grid(source) && range > 0 && !invisible() )
     {
         seen = true;
-        const int midx = mgrd(source);
+        const monsters* mon = monster_at(source);
 
         if (flavour != BEAM_VISUAL
             && !is_tracer
             && !YOU_KILL(thrower)
             && !crawl_state.is_god_acting()
-            && (midx == NON_MONSTER || !you.can_see(&menv[midx])))
+            && (!mon || !you.can_see(mon)))
         {
             mprf("%s appears from out of thin air!",
                  article_a(name, false).c_str());
@@ -1796,8 +1796,8 @@ void bolt::hit_wall()
     else
     {
         // Affect a creature in the wall, if any.
-        if (!invalid_monster_index(mgrd(pos())))
-            affect_monster(&menv[mgrd(pos())]);
+        if (monsters* m = monster_at(pos()))
+            affect_monster(m);
 
         // Regress for explosions: blow up in an open grid (if regressing
         // makes any sense).  Also regress when dropping items.
@@ -1827,12 +1827,9 @@ void bolt::affect_cell()
     const bool was_solid = grid_is_solid(grd(pos()));
     if (was_solid)
     {
-        const int mid = mgrd(pos());
-
         // Some special casing.
-        if (!invalid_monster_index(mid))
+        if (monsters* mon = monster_at(pos()))
         {
-            monsters* const mon = &menv[mid];
             if (can_affect_wall_monster(mon))
                 affect_monster(mon);
             else
@@ -1850,8 +1847,9 @@ void bolt::affect_cell()
 
     // We don't want to hit a monster in a wall square twice.
     const bool still_wall = (was_solid && old_pos == pos());
-    if (!still_wall && !invalid_monster_index(mgrd(pos())))
-        affect_monster(&menv[mgrd(pos())]);
+    if (!still_wall)
+        if (monsters* m = monster_at(pos()))
+            affect_monster(m);
 
     // If the player can ever walk through walls, this will
     // need special-casing too.
@@ -2882,10 +2880,10 @@ void bolt::drop_object()
     {
         if (item->sub_type == MI_THROWING_NET)
         {
+            monsters* m = monster_at(pos());
             // Player or monster on position is caught in net.
             if (you.pos() == pos() && you.attribute[ATTR_HELD]
-                || mgrd(pos()) != NON_MONSTER &&
-                   mons_is_caught(&menv[mgrd(pos())]))
+                || m && mons_is_caught(m))
             {
                 // If no trapping net found mark this one.
                 if (get_trapping_net(pos(), true) == NON_ITEM)
@@ -3103,7 +3101,7 @@ void bolt::affect_place_explosion_clouds()
 
         place_cloud( CLOUD_FIRE, p, duration, whose_kill(), killer() );
 
-        if (grd(p) == DNGN_FLOOR && mgrd(p) == NON_MONSTER
+        if (grd(p) == DNGN_FLOOR && !monster_at(p)
             && one_chance_in(4))
         {
             const god_type god =
@@ -3325,8 +3323,8 @@ void bolt::reflect()
 
     if (pos() == you.pos())
         reflector = NON_MONSTER;
-    else if (mgrd(pos()) != NON_MONSTER)
-        reflector = mgrd(source);
+    else if (monsters* m = monster_at(pos()))
+        reflector = m->mindex();
     else
     {
         reflector = -1;
diff --git a/crawl-ref/source/debug.cc b/crawl-ref/source/debug.cc
index 56ca4312e6..321b11bad3 100644
--- a/crawl-ref/source/debug.cc
+++ b/crawl-ref/source/debug.cc
@@ -5599,10 +5599,7 @@ static void _move_monster(const coord_def& where, int mid1)
     monsters* mon1 = &menv[mid1];
 
     const int mid2 = mgrd(moves.target);
-    monsters* mon2 = NULL;
-
-    if (mid2 != NON_MONSTER)
-        mon2 = &menv[mid2];
+    monsters* mon2 = monster_at(moves.target);
 
     mon1->moveto(moves.target);
     mgrd(moves.target) = mid1;
diff --git a/crawl-ref/source/decks.cc b/crawl-ref/source/decks.cc
index c5b56ffa0c..8e9ca93b77 100644
--- a/crawl-ref/source/decks.cc
+++ b/crawl-ref/source/decks.cc
@@ -1738,14 +1738,12 @@ static int _drain_monsters(coord_def where, int pow, int, actor *)
         drain_exp();
     else
     {
-        const int mnstr = mgrd(where);
-        if (mnstr == NON_MONSTER)
+        monsters* mon = monster_at(where);
+        if (mon == NULL)
             return (0);
 
-        monsters& mon = menv[mnstr];
-
-        if (!mon.drain_exp(&you, false, pow / 50))
-            simple_monster_message(&mon, " is unaffected.");
+        if (mon->drain_exp(&you, false, pow / 50))
+            simple_monster_message(mon, " is unaffected.");
     }
 
     return (1);
@@ -2533,7 +2531,7 @@ static bool _trowel_card(int power, deck_rarity_type rarity)
         {
             // Do-nothing (effectively): create a cosmetic feature
             const coord_def pos = pick_adjacent_free_square(you.pos());
-            if (pos.x >= 0 && pos.y >= 0)
+            if (in_bounds(pos))
             {
                 const dungeon_feature_type statfeat[] = {
                     DNGN_GRANITE_STATUE, DNGN_ORCISH_IDOL
diff --git a/crawl-ref/source/delay.cc b/crawl-ref/source/delay.cc
index 08a7e92d9f..b8caa84917 100644
--- a/crawl-ref/source/delay.cc
+++ b/crawl-ref/source/delay.cc
@@ -83,11 +83,11 @@ static bool _recite_mons_useless(const monsters *mon)
 // Power is maximum 50.
 static int _recite_to_monsters(coord_def where, int pow, int, actor *)
 {
-    const int mon = mgrd(where);
-    if (mon == NON_MONSTER)
-        return (0);
 
-    monsters *mons = &menv[mon];
+    monsters *mons = monster_at(where);
+
+    if (mons == NULL)
+        return (0);
 
     if (_recite_mons_useless(mons))
         return (0);
@@ -676,13 +676,14 @@ int check_recital_audience()
 
     for ( radius_iterator ri(you.pos(), 8); ri; ++ri )
     {
-        if ( mgrd(*ri) == NON_MONSTER )
+        monsters* mons = monster_at(*ri);
+        if (mons == NULL)
             continue;
 
         found_monsters = true;
 
         // Check if audience can listen.
-        if (!_recite_mons_useless( &menv[mgrd(*ri)] ) )
+        if (!_recite_mons_useless(mons))
             return (1);
     }
 
@@ -1139,13 +1140,11 @@ static void _finish_delay(const delay_queue_item &delay)
             }
 
             // Move any monsters out of the way:
-            int mon = mgrd(pass);
-            if (mon != NON_MONSTER)
+            if (monsters* m = monster_at(pass))
             {
-                monsters* m = &menv[mon];
                 // One square, a few squares, anywhere...
                 if (!shift_monster(m) && !monster_blink(m))
-                    monster_teleport( m, true, true );
+                    monster_teleport(m, true, true);
             }
 
             move_player_to_grid(pass, false, true, true);
diff --git a/crawl-ref/source/describe.cc b/crawl-ref/source/describe.cc
index 374348e8cb..39987ff426 100644
--- a/crawl-ref/source/describe.cc
+++ b/crawl-ref/source/describe.cc
@@ -2159,10 +2159,8 @@ void get_feature_desc(const coord_def &pos, describe_info &inf)
     inf.quote = getQuoteString(db_name);
 }
 
-void describe_feature_wide(int x, int y)
+void describe_feature_wide(const coord_def& pos)
 {
-    const coord_def pos(x, y);
-
     describe_info inf;
     get_feature_desc(pos, inf);
     print_description(inf);
@@ -2170,7 +2168,7 @@ void describe_feature_wide(int x, int y)
     mouse_control mc(MOUSE_MODE_MORE);
 
     if (Options.tutorial_left)
-        tutorial_describe_pos(x, y);
+        tutorial_describe_pos(pos.x, pos.y);
 
     if (getch() == 0)
         getch();
diff --git a/crawl-ref/source/describe.h b/crawl-ref/source/describe.h
index 647816ab57..893fbff53c 100644
--- a/crawl-ref/source/describe.h
+++ b/crawl-ref/source/describe.h
@@ -59,11 +59,7 @@ std::string get_item_description( const item_def &item, bool verbose,
  * *********************************************************************** */
 void describe_god( god_type which_god, bool give_title );
 
-// last updated 12 Jun 2008 {jpeg}
-/* ***********************************************************************
- * called from: directn
- * *********************************************************************** */
-void describe_feature_wide(int x, int y);
+void describe_feature_wide(const coord_def& pos);
 void get_feature_desc(const coord_def &gc, describe_info &inf);
 
 // last updated 24 Dec 2008 {mpc}
diff --git a/crawl-ref/source/directn.cc b/crawl-ref/source/directn.cc
index 4ba3d94528..80077397b1 100644
--- a/crawl-ref/source/directn.cc
+++ b/crawl-ref/source/directn.cc
@@ -263,10 +263,8 @@ static void draw_ray_glyph(const coord_def &pos, int colour,
 #ifdef USE_TILE
     tile_place_ray(pos, in_range);
 #else
-    int mid = mgrd(pos);
-    if (mid != NON_MONSTER)
+    if (const monsters *mons = monster_at(pos))
     {
-        const monsters *mons = &menv[mid];
         if (mons->alive() && player_monster_visible(mons))
         {
             glych  = get_screen_glyph(pos.x, pos.y);
@@ -1057,7 +1055,7 @@ void direction(dist& moves, targeting_type restricts,
         if (skip_iter)
             old_target.x += 500; // hmmm...hack
 
-        int i, mid;
+        int i;
 
 #ifndef USE_TILE
         if (key_command >= CMD_TARGET_CYCLE_MLIST
@@ -1269,11 +1267,11 @@ void direction(dist& moves, targeting_type restricts,
             }
             // intentional fall-through
         case CMD_TARGET_SELECT: // finalize current choice
-            if (!moves.isEndpoint
-                && mgrd(moves.target) != NON_MONSTER
-                && _mon_submerged_in_water(&menv[mgrd(moves.target)]))
+            if (!moves.isEndpoint)
             {
-                moves.isEndpoint = true;
+                const monsters* m = monster_at(moves.target);
+                if (m && _mon_submerged_in_water(m))
+                    moves.isEndpoint = true;
             }
             moves.isValid  = true;
             moves.isTarget = true;
@@ -1282,10 +1280,8 @@ void direction(dist& moves, targeting_type restricts,
             you.prev_grd_targ.reset();
 
             // Maybe we should except just_looking here?
-            mid = mgrd(moves.target);
-
-            if (mid != NON_MONSTER)
-                you.prev_targ = mid;
+            if (const monsters* m = monster_at(moves.target))
+                you.prev_targ = m->mindex();
             else if (moves.target == you.pos())
                 you.prev_targ = MHITYOU;
             else
@@ -1343,13 +1339,13 @@ void direction(dist& moves, targeting_type restricts,
             if (!you.wizard || !in_bounds(moves.target))
                 break;
 
-            mid = mgrd(moves.target);
-            if (mid == NON_MONSTER) // can put in terrain description here
-                break;
-
             {
-                monsters &m = menv[mid];
-                mon_attitude_type att = m.attitude;
+                monsters* m = monster_at(moves.target);
+
+                if (m == NULL)
+                    break;
+
+                mon_attitude_type att = m->attitude;
 
                 // During arena mode, skip directly from friendly to hostile.
                 if (crawl_state.arena_suspended && att == ATT_FRIENDLY)
@@ -1357,24 +1353,22 @@ void direction(dist& moves, targeting_type restricts,
 
                 switch (att)
                 {
-                 case ATT_FRIENDLY:
-                     m.attitude = ATT_GOOD_NEUTRAL;
-                     m.flags &= ~MF_CREATED_FRIENDLY;
-                     m.flags |= MF_WAS_NEUTRAL;
-                     break;
-                 case ATT_GOOD_NEUTRAL:
-                     m.attitude = ATT_NEUTRAL;
-                     break;
-                 case ATT_NEUTRAL:
-                     m.attitude = ATT_HOSTILE;
-                     m.flags &= ~MF_WAS_NEUTRAL;
-                     break;
-                 case ATT_HOSTILE:
-                     m.attitude = ATT_FRIENDLY;
-                     m.flags |= MF_CREATED_FRIENDLY;
-                     break;
-                 default:
-                     break;
+                case ATT_FRIENDLY:
+                    m->attitude = ATT_GOOD_NEUTRAL;
+                    m->flags &= ~MF_CREATED_FRIENDLY;
+                    m->flags |= MF_WAS_NEUTRAL;
+                    break;
+                case ATT_GOOD_NEUTRAL:
+                    m->attitude = ATT_NEUTRAL;
+                    break;
+                case ATT_NEUTRAL:
+                    m->attitude = ATT_HOSTILE;
+                    m->flags &= ~MF_WAS_NEUTRAL;
+                    break;
+                case ATT_HOSTILE:
+                    m->attitude = ATT_FRIENDLY;
+                    m->flags |= MF_CREATED_FRIENDLY;
+                    break;
                 }
 
                 // To update visual branding of friendlies.  Only
@@ -1387,32 +1381,22 @@ void direction(dist& moves, targeting_type restricts,
         case CMD_TARGET_WIZARD_BLESS_MONSTER:
             if (!you.wizard || !in_bounds(moves.target))
                 break;
-            mid = mgrd(moves.target);
-            if (mid == NON_MONSTER) // can put in terrain description here
-                break;
-
-            wizard_apply_monster_blessing(&menv[mid]);
+            if (monsters* m = monster_at(moves.target))
+                wizard_apply_monster_blessing(m);
             break;
 
         case CMD_TARGET_WIZARD_MAKE_SHOUT:
-            // Maybe we can skip this check...but it can't hurt
             if (!you.wizard || !in_bounds(moves.target))
                 break;
-            mid = mgrd(moves.target);
-            if (mid == NON_MONSTER) // can put in terrain description here
-                break;
-
-            debug_make_monster_shout(&menv[mid]);
+            if (monsters* m = monster_at(moves.target))
+                debug_make_monster_shout(m);
             break;
 
         case CMD_TARGET_WIZARD_GIVE_ITEM:
             if (!you.wizard || !in_bounds(moves.target))
                 break;
-            mid = mgrd(moves.target);
-            if (mid == NON_MONSTER) // can put in terrain description here
-                break;
-
-            wizard_give_monster_item(&menv[mid]);
+            if (monsters* m = monster_at(moves.target))
+                wizard_give_monster_item(m);
             break;
 
         case CMD_TARGET_WIZARD_MOVE:
@@ -1428,11 +1412,9 @@ void direction(dist& moves, targeting_type restricts,
         case CMD_TARGET_WIZARD_PATHFIND:
             if (!you.wizard || !in_bounds(moves.target))
                 break;
-            mid = mgrd(moves.target);
-            if (mid == NON_MONSTER)
-                break;
 
-            debug_pathfind(mid);
+            if (monsters* m = monster_at(moves.target))
+                debug_pathfind(m->mindex());
             break;
 
         case CMD_TARGET_WIZARD_GAIN_LEVEL:
@@ -1441,31 +1423,24 @@ void direction(dist& moves, targeting_type restricts,
         case CMD_TARGET_WIZARD_MISCAST:
             if (!you.wizard || !in_bounds(moves.target))
                 break;
-            mid = mgrd(moves.target);
-            if (mid == NON_MONSTER && you.pos() != moves.target)
-                break;
-
-            debug_miscast(mid);
+            if (you.pos() == moves.target)
+                debug_miscast(NON_MONSTER);
+            if (monsters* m = monster_at(moves.target))
+                debug_miscast(m->mindex());
             break;
 
         case CMD_TARGET_WIZARD_MAKE_SUMMONED:
             if (!you.wizard || !in_bounds(moves.target))
                 break;
-            mid = mgrd(moves.target);
-            if (mid == NON_MONSTER) // can put in terrain description here
-                break;
-
-            wizard_make_monster_summoned(&menv[mid]);
+            if (monsters* m = monster_at(moves.target))
+                wizard_make_monster_summoned(m);
             break;
 
         case CMD_TARGET_WIZARD_POLYMORPH:
             if (!you.wizard || !in_bounds(moves.target))
                 break;
-            mid = mgrd(moves.target);
-            if (mid == NON_MONSTER) // can put in terrain description here
-                break;
-
-            wizard_polymorph_monster(&menv[mid]);
+            if (monsters* m = monster_at(moves.target))
+                wizard_polymorph_monster(m);
             break;
 
 #endif
@@ -1629,9 +1604,9 @@ std::string get_terse_square_desc(const coord_def &gc)
         else
             desc = unseen_desc;
     }
-    else if (mgrd(gc) != NON_MONSTER && you.can_see(&menv[mgrd(gc)]))
+    else if (monster_at(gc) && you.can_see(monster_at(gc)))
     {
-        const monsters &mons = menv[mgrd(gc)];
+        const monsters& mons = *monster_at(gc);
 
         if (mons_is_mimic(mons.type) && !(mons.flags & MF_KNOWN_MIMIC))
         {
@@ -1663,16 +1638,16 @@ void get_square_desc(const coord_def &c, describe_info &inf)
     // NOTE: Keep this function in sync with full_describe_square.
 
     // Don't give out information for things outside LOS
-    if (!see_grid(c.x, c.y))
+    if (!see_grid(c))
         return;
 
-    const int mid = mgrd(c);
+    const monsters* mons = monster_at(c);
     const int oid = igrd(c);
 
-    if (mid != NON_MONSTER && player_monster_visible(&menv[mid]))
+    if (mons && player_monster_visible(mons))
     {
         // First priority: monsters.
-        get_monster_desc(menv[mid], inf);
+        get_monster_desc(*mons, inf);
     }
     else if (oid != NON_ITEM)
     {
@@ -1691,16 +1666,16 @@ void full_describe_square(const coord_def &c)
     // NOTE: Keep this function in sync with get_square_desc.
 
     // Don't give out information for things outside LOS
-    if (!see_grid(c.x, c.y))
+    if (!see_grid(c))
         return;
 
-    const int mid = mgrd(c);
+    const monsters* mons = monster_at(c);
     const int oid = igrd(c);
 
-    if (mid != NON_MONSTER && player_monster_visible(&menv[mid]))
+    if (mons && player_monster_visible(mons))
     {
         // First priority: monsters.
-        describe_monsters(menv[mid]);
+        describe_monsters(*mons);
     }
     else if (oid != NON_ITEM)
     {
@@ -1710,7 +1685,7 @@ void full_describe_square(const coord_def &c)
     else
     {
         // Third priority: features.
-        describe_feature_wide(c.x, c.y);
+        describe_feature_wide(c);
     }
 
     redraw_screen();
@@ -1782,7 +1757,7 @@ bool in_los(const coord_def& pos)
     return (in_vlos(grid2view(pos)));
 }
 
-static bool _mons_is_valid_target(monsters *mon, int mode, int range)
+static bool _mons_is_valid_target(const monsters *mon, int mode, int range)
 {
     // Unknown mimics don't count as monsters, either.
     if (mons_is_mimic(mon->type)
@@ -1810,18 +1785,18 @@ static bool _mons_is_valid_target(monsters *mon, int mode, int range)
 static bool _find_mlist( const coord_def& where, int idx, bool need_path,
                          int range = -1)
 {
-    if ((int) mlist.size() <= idx)
+    if (static_cast<int>(mlist.size()) <= idx)
         return (false);
 
     if (!_is_target_in_range(where, range) || !in_los(where))
         return (false);
 
-    const int targ_mon = mgrd(where);
-    if (targ_mon == NON_MONSTER)
+    const monsters* mon = monster_at(where);
+    if (mon == NULL)
         return (false);
 
     int real_idx = 0;
-    for (unsigned int i = 0; i < mlist.size()-1; i++)
+    for (unsigned int i = 0; i+1 < mlist.size(); i++)
     {
         if (real_idx == idx)
         {
@@ -1836,8 +1811,6 @@ static bool _find_mlist( const coord_def& where, int idx, bool need_path,
         real_idx++;
    }
 
-    monsters *mon  = &menv[targ_mon];
-
     if (!_mons_is_valid_target(mon, TARG_ANY, range))
         return (false);
 
@@ -1878,18 +1851,16 @@ static bool _find_monster( const coord_def& where, int mode, bool need_path,
     if (!_is_target_in_range(where, range))
         return (false);
 
-    const int targ_mon = mgrd(where);
+    const monsters* mon = monster_at(where);
 
     // No monster or outside LOS.
-    if (targ_mon == NON_MONSTER || !in_los(where))
+    if (mon == NULL || !in_los(where))
         return (false);
 
     // Monster in LOS but only via glass walls, so no direct path.
     if (need_path && !see_grid_no_trans(where))
         return (false);
 
-    monsters *mon = &menv[targ_mon];
-
     if (!_mons_is_valid_target(mon, mode, range))
         return (false);
 
@@ -1898,15 +1869,15 @@ static bool _find_monster( const coord_def& where, int mode, bool need_path,
         return (true);
 
     if (mode == TARG_FRIEND)
-        return (mons_friendly(&menv[targ_mon] ));
+        return (mons_friendly(mon));
 
     ASSERT(mode == TARG_ENEMY);
-    if (mons_friendly(&menv[targ_mon]))
+    if (mons_friendly(mon))
         return (false);
 
     // Don't target zero xp monsters, unless target_zero_exp is set.
     return (Options.target_zero_exp
-            || !mons_class_flag( menv[targ_mon].type, M_NO_EXP_GAIN ));
+            || !mons_class_flag(mon->type, M_NO_EXP_GAIN));
 }
 
 static bool _find_feature( const coord_def& where, int mode,
@@ -1924,11 +1895,11 @@ static bool _find_object(const coord_def& where, int mode,
 {
     // First, check for mimics.
     bool is_mimic = false;
-    const int mons = mgrd(where);
-    if (mons != NON_MONSTER
-        && player_monster_visible( &(menv[mons]) )
-        && mons_is_mimic(menv[mons].type)
-        && !(menv[mons].flags & MF_KNOWN_MIMIC))
+    const monsters* m = monster_at(where);
+    if (m
+        && player_monster_visible(m)
+        && mons_is_mimic(m->type)
+        && !(m->flags & MF_KNOWN_MIMIC))
     {
         is_mimic = true;
     }
@@ -3124,10 +3095,8 @@ static void _describe_cell(const coord_def& where, bool in_range)
     if (where == you.pos() && !crawl_state.arena_suspended)
         mpr("You.", MSGCH_EXAMINE_FILTER);
 
-    if (mgrd(where) != NON_MONSTER)
+    if (const monsters* mon = monster_at(where))
     {
-        const monsters* mon = &menv[mgrd(where)];
-
         if (_mon_submerged_in_water(mon))
         {
             mpr("There is a strange disturbance in the water here.",
diff --git a/crawl-ref/source/effects.cc b/crawl-ref/source/effects.cc
index 300a5a8ded..b5766f12e1 100644
--- a/crawl-ref/source/effects.cc
+++ b/crawl-ref/source/effects.cc
@@ -122,13 +122,10 @@ int holy_word_monsters(coord_def where, int pow, int caster,
         retval = holy_word_player(pow, caster, attacker);
 
     // Is a monster in this cell?
-    const int mon = mgrd(where);
-
-    if (mon == NON_MONSTER)
+    monsters *monster = monster_at(where);
+    if (monster == NULL)
         return (retval);
 
-    monsters *monster = &menv[mon];
-
     if (!monster->alive() || !mons_is_unholy(monster))
         return (retval);
 
@@ -265,13 +262,10 @@ int torment_monsters(coord_def where, int pow, int caster, actor *attacker)
         retval = torment_player(0, caster);
 
     // Is a monster in this cell?
-    const int mon = mgrd(where);
-
-    if (mon == NON_MONSTER)
+    monsters *monster = monster_at(where);
+    if (monster == NULL)
         return (retval);
 
-    monsters *monster = &menv[mon];
-
     if (!monster->alive() || mons_res_negative_energy(monster) == 3)
         return (retval);
 
@@ -2231,7 +2225,7 @@ void yell(bool force)
         }
 
         mpr("Gang up on whom?", MSGCH_PROMPT);
-        direction( targ, DIR_TARGET, TARG_ENEMY, -1, false, false );
+        direction(targ, DIR_TARGET, TARG_ENEMY, -1, false, false);
 
         if (targ.isCancel)
         {
@@ -2239,14 +2233,22 @@ void yell(bool force)
             return;
         }
 
-        if (!targ.isValid || mgrd(targ.target) == NON_MONSTER
-            || !player_monster_visible(&env.mons[mgrd(targ.target)]))
         {
-            mpr("Yeah, whatever.");
-            return;
-        }
+            bool cancel = !targ.isValid;
+            if (!cancel)
+            {
+                const monsters* m = monster_at(targ.target);
+                cancel = (m == NULL || !you.can_see(m));
+                if (!cancel)
+                    mons_targd = m->mindex();
+            }
 
-        mons_targd = mgrd(targ.target);
+            if (cancel)
+            {
+                mpr("Yeah, whatever.");
+                return;
+            }
+        }
         break;
 
     default:
@@ -2795,7 +2797,7 @@ void change_labyrinth(bool msg)
                 continue;
 
             // We don't want to deal with monsters being shifted around.
-            if (mgrd(p) != NON_MONSTER)
+            if (monster_at(p))
                 continue;
 
             // Do not pick a grid right next to the original wall.
@@ -3555,7 +3557,7 @@ static void _catchup_monster_moves(monsters *mon, int turns)
         const coord_def next(pos + inc);
         const dungeon_feature_type feat = grd(next);
         if (grid_is_solid(feat)
-            || mgrd(next) != NON_MONSTER
+            || monster_at(next)
             || !monster_habitable_grid(mon, feat))
         {
             break;
diff --git a/crawl-ref/source/files.cc b/crawl-ref/source/files.cc
index ae58bc66d8..10833e6141 100644
--- a/crawl-ref/source/files.cc
+++ b/crawl-ref/source/files.cc
@@ -962,11 +962,10 @@ static void _grab_followers()
     // Handle nearby ghosts.
     for (adjacent_iterator ai; ai; ++ai)
     {
-        if (mgrd(*ai) == NON_MONSTER)
+        monsters *fmenv = monster_at(*ai);
+        if (fmenv == NULL)
             continue;
 
-        monsters *fmenv = &menv[mgrd(*ai)];
-
         if (fmenv->type == MONS_PLAYER_GHOST
             && fmenv->hit_points < fmenv->max_hit_points / 2)
         {
diff --git a/crawl-ref/source/it_use3.cc b/crawl-ref/source/it_use3.cc
index 460059ad27..21e50531bc 100644
--- a/crawl-ref/source/it_use3.cc
+++ b/crawl-ref/source/it_use3.cc
@@ -268,6 +268,7 @@ static bool _reaching_weapon_attack(const item_def& wpn)
     const coord_def delta = beam.target - you.pos();
     const int x_distance = abs(delta.x);
     const int y_distance = abs(delta.y);
+    monsters* mons = monster_at(beam.target);
 
     if (x_distance > 2 || y_distance > 2)
     {
@@ -279,12 +280,10 @@ static bool _reaching_weapon_attack(const item_def& wpn)
         mpr("There's a wall in the way.");
         return (false);
     }
-    else if (mgrd(beam.target) == NON_MONSTER)
+    else if (mons == NULL)
     {
         // Must return true, otherwise you get a free discovery
-        // of invisible monsters. Maybe we shouldn't do practice
-        // here to prevent scumming...but that would just encourage
-        // finding popcorn monsters.
+        // of invisible monsters.
         mpr("You attack empty space.");
         return (true);
     }
@@ -310,7 +309,7 @@ static bool _reaching_weapon_attack(const item_def& wpn)
             if (x_chance_in_y(5 + (3 * skill), 40))
             {
                 mpr("You reach to attack!");
-                success = you_attack(mgrd(beam.target), false);
+                success = you_attack(mons->mindex(), false);
             }
             else
             {
@@ -321,22 +320,19 @@ static bool _reaching_weapon_attack(const item_def& wpn)
         else
         {
             mpr("You reach to attack!");
-            success = you_attack(mgrd(beam.target), false);
+            success = you_attack(mons->mindex(), false);
         }
 
         if (success)
         {
-            int mid = mgrd(beam.target);
-            if (mid != NON_MONSTER)
-            {
-                monsters *mon = &menv[mgrd(beam.target)];
-                if (mons_is_mimic( mon->type ))
-                    mimic_alert(mon);
-            }
+            // Monster might have died or gone away.
+            if (monsters* m = monster_at(beam.target))
+                if (mons_is_mimic(m->type))
+                    mimic_alert(m);
         }
     }
     else
-        you_attack(mgrd(beam.target), false);
+        you_attack(mons->mindex(), false);
 
     return (true);
 }
diff --git a/crawl-ref/source/misc.cc b/crawl-ref/source/misc.cc
index e419a646fc..a3c77d2036 100644
--- a/crawl-ref/source/misc.cc
+++ b/crawl-ref/source/misc.cc
@@ -2669,10 +2669,8 @@ std::vector<monsters*> get_nearby_monsters(bool want_move,
     // Sweep every visible square within range.
     for (radius_iterator ri(you.pos(), range); ri; ++ri)
     {
-        const unsigned short targ_monst = env.mgrid(*ri);
-        if (targ_monst != NON_MONSTER)
+        if (monsters* mon = monster_at(*ri))
         {
-            monsters *mon = &menv[targ_monst];
             if (mon->alive()
                 && (!require_visible || player_monster_visible(mon))
                 && !mons_is_submerged(mon)
@@ -2682,7 +2680,7 @@ std::vector<monsters*> get_nearby_monsters(bool want_move,
             {
                 mons.push_back(mon);
                 if (just_check) // stop once you find one
-                    return mons;
+                    break;
             }
         }
     }
@@ -2908,23 +2906,12 @@ coord_def pick_adjacent_free_square(const coord_def& p)
 {
     int num_ok = 0;
     coord_def result(-1, -1);
-    for ( int ux = p.x-1; ux <= p.x+1; ++ux )
-    {
-        for ( int uy = p.y-1; uy <= p.y+1; ++uy )
-        {
-            if ( ux == p.x && uy == p.y )
-                continue;
 
-            if ( in_bounds(ux, uy)
-                 && grd[ux][uy] == DNGN_FLOOR
-                 && mgrd[ux][uy] == NON_MONSTER )
-            {
-                ++num_ok;
-                if ( one_chance_in(num_ok) )
-                    result.set(ux, uy);
-            }
-        }
-    }
+    for (adjacent_iterator ai(p); ai; ++ai)
+        if (grd(*ai) == DNGN_FLOOR && monster_at(*ai) == NULL)
+            if (one_chance_in(++num_ok))
+                result = *ai;
+
     return result;
 }
 
diff --git a/crawl-ref/source/mtransit.cc b/crawl-ref/source/mtransit.cc
index 14f37c4d66..9d99782177 100644
--- a/crawl-ref/source/mtransit.cc
+++ b/crawl-ref/source/mtransit.cc
@@ -270,7 +270,7 @@ bool follower::place(bool near_player)
                     near_player = true;
                 else
                 {
-                    mgrd[where_to_go.x][where_to_go.y] = monster_index(&m);
+                    mgrd(where_to_go) = m.mindex();
                     placed = true;
                 }
             }
diff --git a/crawl-ref/source/religion.cc b/crawl-ref/source/religion.cc
index 71836b9561..8987d02123 100644
--- a/crawl-ref/source/religion.cc
+++ b/crawl-ref/source/religion.cc
@@ -5354,11 +5354,10 @@ static bool _yred_slaves_abandon_you()
     {
         for (radius_iterator ri(you.pos(), 9); ri; ++ri)
         {
-            if (mgrd(*ri) == NON_MONSTER)
+            monsters *monster = monster_at(*ri);
+            if (monster == NULL)
                 continue;
 
-            monsters *monster = &menv[mgrd(*ri)];
-
             if (_is_yred_enslaved_body_and_soul(monster)
                 || is_yred_undead_slave(monster))
             {
@@ -5432,11 +5431,10 @@ static bool _beogh_followers_abandon_you()
     {
         for (radius_iterator ri(you.pos(), 9); ri; ++ri)
         {
-            if (mgrd(*ri) == NON_MONSTER)
+            monsters *monster = monster_at(*ri);
+            if (monster == NULL)
                 continue;
 
-            monsters *monster = &menv[mgrd(*ri)];
-
             if (is_orcish_follower(monster))
             {
                 num_followers++;
diff --git a/crawl-ref/source/spells1.cc b/crawl-ref/source/spells1.cc
index a520d86637..c807b6445c 100644
--- a/crawl-ref/source/spells1.cc
+++ b/crawl-ref/source/spells1.cc
@@ -162,8 +162,7 @@ int blink(int pow, bool high_level_controlled_blink, bool wizard_blink)
         if (wizard_blink && grid_is_solid(grd(beam.target)))
             grd(beam.target) = DNGN_FLOOR;
 
-        if (grid_is_solid(grd(beam.target))
-            || mgrd(beam.target) != NON_MONSTER)
+        if (grid_is_solid(grd(beam.target)) || monster_at(beam.target))
         {
             mpr("Oops! Maybe something was there already.");
             random_blink(false);
@@ -532,9 +531,9 @@ bool conjure_flame(int pow)
 
         const int cloud = env.cgrid(spelld.target);
 
-        if (grid_is_solid(grd(spelld.target)) ||
-            mgrd(spelld.target) != NON_MONSTER ||
-            (cloud != EMPTY_CLOUD && env.cloud[cloud].type != CLOUD_FIRE))
+        if (grid_is_solid(grd(spelld.target))
+            || monster_at(spelld.target)
+            || (cloud != EMPTY_CLOUD && env.cloud[cloud].type != CLOUD_FIRE))
         {
             mpr( "There's already something there!" );
             continue;
diff --git a/crawl-ref/source/spells2.cc b/crawl-ref/source/spells2.cc
index 508a83cb94..7188bc8bf4 100644
--- a/crawl-ref/source/spells2.cc
+++ b/crawl-ref/source/spells2.cc
@@ -198,9 +198,8 @@ int detect_creatures( int pow, bool telepathic )
 
     for (radius_iterator ri(you.pos(), map_radius, true, false); ri; ++ri)
     {
-        if (mgrd(*ri) != NON_MONSTER)
+        if (monsters *mon = monster_at(*ri))
         {
-            monsters *mon = &menv[ mgrd(*ri) ];
             creatures_found++;
 
             _mark_detected_creature(*ri, mon, fuzz_chance, fuzz_radius);
@@ -758,16 +757,14 @@ void drain_life(int pow)
 
 bool vampiric_drain(int pow, const dist &vmove)
 {
-    int mgr = mgrd(you.pos() + vmove.delta);
+    monsters *monster = monster_at(you.pos() + vmove.delta);
 
-    if (mgr == NON_MONSTER)
+    if (monster == NULL)
     {
         mpr("There isn't anything there!");
         return (false);
     }
 
-    monsters *monster = &menv[mgr];
-
     god_conduct_trigger conducts[3];
     disable_attack_conducts(conducts);
 
@@ -1350,9 +1347,9 @@ bool cast_summon_elemental(int pow, god_type god,
 
         targ = you.pos() + smove.delta;
 
-        if (mgrd(targ) != NON_MONSTER)
+        if (const monsters *m = monster_at(targ))
         {
-            if (player_monster_visible(&menv[mgrd(targ)]))
+            if (you.can_see(m))
                 mpr("There's something there already!");
             else
             {
diff --git a/crawl-ref/source/spells3.cc b/crawl-ref/source/spells3.cc
index ce60981602..145d90aa63 100644
--- a/crawl-ref/source/spells3.cc
+++ b/crawl-ref/source/spells3.cc
@@ -186,7 +186,9 @@ bool detect_curse(bool suppress_msg)
 
 bool cast_smiting(int power, const coord_def& where)
 {
-    if (invalid_monster_index(mgrd(where)))
+    monsters *m = monster_at(where);
+
+    if (m == NULL)
     {
         mpr("There's nothing there!");
         // Counts as a real cast, due to victory-dancing and
@@ -194,22 +196,20 @@ bool cast_smiting(int power, const coord_def& where)
         return (true);
     }
 
-    monsters& m = menv[mgrd(where)];
-
     god_conduct_trigger conducts[3];
     disable_attack_conducts(conducts);
 
-    const bool success = !stop_attack_prompt(&m, false, false);
+    const bool success = !stop_attack_prompt(m, false, false);
 
     if (success)
     {
-        set_attack_conducts(conducts, &m);
+        set_attack_conducts(conducts, m);
 
-        mprf("You smite %s!", m.name(DESC_NOCAP_THE).c_str());
+        mprf("You smite %s!", m->name(DESC_NOCAP_THE).c_str());
 
-        behaviour_event(&m, ME_ANNOY, MHITYOU);
-        if (mons_is_mimic(m.type))
-            mimic_alert(&m);
+        behaviour_event(m, ME_ANNOY, MHITYOU);
+        if (mons_is_mimic(m->type))
+            mimic_alert(m);
     }
 
     enable_attack_conducts(conducts);
@@ -219,9 +219,9 @@ bool cast_smiting(int power, const coord_def& where)
         // Maxes out at around 40 damage at 27 Invocations, which is
         // plenty in my book (the old max damage was around 70,
         // which seems excessive).
-        m.hurt(&you, 7 + (random2(power) * 33 / 191));
-        if (m.alive())
-            print_wounds(&m);
+        m->hurt(&you, 7 + (random2(power) * 33 / 191));
+        if (m->alive())
+            print_wounds(m);
     }
 
     return (success);
@@ -231,12 +231,12 @@ int airstrike(int power, dist &beam)
 {
     bool success = false;
 
-    if (mgrd(beam.target) == NON_MONSTER || beam.isMe)
+    monsters *monster = monster_at(beam.target);
+
+    if (monster == NULL)
         canned_msg(MSG_SPELL_FIZZLES);
     else
     {
-        monsters *monster = &menv[mgrd(beam.target)];
-
         god_conduct_trigger conducts[3];
         disable_attack_conducts(conducts);
 
@@ -1330,7 +1330,7 @@ static bool _teleport_player( bool allow_control, bool new_abyss_area )
 
             if (grd(you.pos()) != DNGN_FLOOR
                     && grd(you.pos()) != DNGN_SHALLOW_WATER
-                || mgrd(you.pos()) != NON_MONSTER
+                || monster_at(you.pos())
                 || env.cgrid(you.pos()) != EMPTY_CLOUD)
             {
                 is_controlled = false;
@@ -1382,7 +1382,7 @@ static bool _teleport_player( bool allow_control, bool new_abyss_area )
         }
         while (grd(newpos) != DNGN_FLOOR
                    && grd(newpos) != DNGN_SHALLOW_WATER
-               || mgrd(newpos) != NON_MONSTER
+               || monster_at(newpos)
                || env.cgrid(newpos) != EMPTY_CLOUD
                || need_distance_check && (newpos - centre).abs() < 34*34);
 
@@ -1444,7 +1444,7 @@ bool entomb(int powc)
     for ( adjacent_iterator ai; ai; ++ai )
     {
         // Tile already occupied by monster
-        if (mgrd(*ai) != NON_MONSTER)
+        if (monster_at(*ai))
             continue;
 
         // This is where power comes in.
@@ -1703,11 +1703,8 @@ bool cast_sanctuary(const int power)
         // scare all attacking monsters inside sanctuary, and make
         // all friendly monsters inside sanctuary stop attacking and
         // move towards the player.
-        int monster = mgrd(pos);
-        if (monster != NON_MONSTER)
+        if (monsters* mon = monster_at(pos))
         {
-            monsters* mon = &menv[monster];
-
             if (mons_friendly(mon))
             {
                 mon->foe       = MHITYOU;
diff --git a/crawl-ref/source/spells4.cc b/crawl-ref/source/spells4.cc
index ef1c31ffb9..5d18ebabb0 100644
--- a/crawl-ref/source/spells4.cc
+++ b/crawl-ref/source/spells4.cc
@@ -393,33 +393,30 @@ void cast_detect_secret_doors(int pow)
 
 static int _sleep_monsters(coord_def where, int pow, int, actor *)
 {
-    const int mnstr = mgrd(where);
-
-    if (mnstr == NON_MONSTER)
-        return 0;
-
-    monsters& mon = menv[mnstr];
+    monsters *monster = monster_at(where);
+    if (monster == NULL)
+        return (0);
 
-    if (mons_holiness(&mon) != MH_NATURAL)
-        return 0;
-    if (check_mons_resist_magic( &mon, pow ))
-        return 0;
+    if (mons_holiness(monster) != MH_NATURAL)
+        return (0);
+    if (check_mons_resist_magic(monster, pow))
+        return (0);
 
     // Works on friendlies too, so no check for that.
 
     //jmf: Now that sleep == hibernation:
-    const int res = mons_res_cold( &mon );
+    const int res = mons_res_cold(monster);
     if (res > 0 && one_chance_in(std::max(4 - res, 1)))
-        return 0;
-    if (mon.has_ench(ENCH_SLEEP_WARY) && !one_chance_in(3))
-        return 0;
+        return (0);
+    if (monster->has_ench(ENCH_SLEEP_WARY) && !one_chance_in(3))
+        return (0);
 
-    mon.put_to_sleep();
+    monster->put_to_sleep();
 
-    if (mons_class_flag( mon.type, M_COLD_BLOOD ) && coinflip())
-        mon.add_ench(ENCH_SLOW);
+    if (mons_class_flag( monster->type, M_COLD_BLOOD ) && coinflip())
+        monster->add_ench(ENCH_SLOW);
 
-    return 1;
+    return (1);
 }
 
 void cast_mass_sleep(int pow)
@@ -451,13 +448,10 @@ static bool _is_domesticated_animal(int type)
 
 static int _tame_beast_monsters(coord_def where, int pow, int, actor *)
 {
-    const int which_mons = mgrd(where);
-
-    if (which_mons == NON_MONSTER)
+    monsters *monster = monster_at(where);
+    if (monster == NULL)
         return 0;
 
-    monsters *monster = &menv[which_mons];
-
     if (!_is_domesticated_animal(monster->type) || mons_friendly(monster)
         || player_will_anger_monster(monster))
     {
@@ -561,14 +555,12 @@ static int _ignite_poison_monsters(coord_def where, int pow, int, actor *)
     bolt beam;
     beam.flavour = BEAM_FIRE;   // This is dumb, only used for adjust!
 
-    dice_def  dam_dice( 0, 5 + pow / 7 );  // Dice added below if applicable.
+    dice_def dam_dice(0, 5 + pow/7);  // Dice added below if applicable.
 
-    const int mon_index = mgrd(where);
-    if (mon_index == NON_MONSTER)
+    monsters *mon = monster_at(where);
+    if (mon == NULL)
         return (0);
 
-    struct monsters *const mon = &menv[ mon_index ];
-
     // Monsters which have poison corpses or poisonous attacks.
     if (mons_is_poisoner(mon))
         dam_dice.num = 3;
@@ -595,7 +587,7 @@ static int _ignite_poison_monsters(coord_def where, int pow, int, actor *)
              dam_dice.num, dam_dice.size, damage );
 #endif
 
-        if (!_player_hurt_monster( mon_index, damage ))
+        if (!_player_hurt_monster(mon->mindex(), damage))
         {
             // Monster survived, remove any poison.
             mon->del_ench(ENCH_POISON);
@@ -776,7 +768,7 @@ void cast_silence(int pow)
 
 static int _discharge_monsters(coord_def where, int pow, int, actor *)
 {
-    const int mon = mgrd(where);
+    monsters *monster = monster_at(where);
     int damage = 0;
 
     bolt beam;
@@ -791,20 +783,20 @@ static int _discharge_monsters(coord_def where, int pow, int, actor *)
             damage /= 2;
         ouch(damage, NON_MONSTER, KILLED_BY_WILD_MAGIC);
     }
-    else if (mon == NON_MONSTER)
+    else if (monster == NULL)
         return (0);
-    else if (mons_res_elec(&menv[mon]) > 0 || mons_flies(&menv[mon]))
+    else if (mons_res_elec(monster) > 0 || mons_flies(monster))
         return (0);
     else
     {
-        damage = 3 + random2( 5 + pow / 10 );
-        damage = mons_adjust_flavoured( &menv[mon], beam, damage );
+        damage = 3 + random2(5 + pow/10);
+        damage = mons_adjust_flavoured(monster, beam, damage );
 
         if (damage)
         {
             mprf("%s is struck by lightning.",
-                 menv[mon].name(DESC_CAP_THE).c_str());
-            _player_hurt_monster(mon, damage);
+                 monster->name(DESC_CAP_THE).c_str());
+            _player_hurt_monster(*monster, damage);
         }
     }
 
@@ -880,13 +872,11 @@ static int _distortion_monsters(coord_def where, int pow, int, actor *)
         return (1);
     }
 
-    int monster_attacked = mgrd(where);
-
-    if (monster_attacked == NON_MONSTER)
-        return 0;
+    monsters *defender = monster_at(where);
+    if (defender == NULL)
+        return (0);
 
     int specdam = 0;
-    monsters *defender = &menv[monster_attacked];
 
     if (defender->type == MONS_BLINK_FROG
         || defender->type == MONS_PRINCE_RIBBIT)      // any others resist?
@@ -938,7 +928,7 @@ static int _distortion_monsters(coord_def where, int pow, int, actor *)
         return 1;
     }
 
-    _player_hurt_monster(monster_attacked, specdam);
+    _player_hurt_monster(*defender, specdam);
 
     return (specdam);
 }
@@ -953,13 +943,10 @@ void cast_bend(int pow)
 // the insane damage potential.  -- bwr
 int disperse_monsters(coord_def where, int pow, int, actor *)
 {
-    const int monster_attacked = mgrd(where);
-
-    if (monster_attacked == NON_MONSTER)
+    monsters *defender = monster_at(where);
+    if (defender == NULL)
         return 0;
 
-    monsters *defender = &menv[monster_attacked];
-
     if (defender->type == MONS_BLINK_FROG
         || defender->type == MONS_PRINCE_RIBBIT)
     {
@@ -996,12 +983,9 @@ void cast_dispersal(int pow)
 
 static int _spell_swap_func(coord_def where, int pow, int, actor *)
 {
-    int monster_attacked = mgrd(where);
-
-    if (monster_attacked == NON_MONSTER)
-        return 0;
-
-    monsters *defender = &menv[monster_attacked];
+    monsters *defender = monster_at(where);
+    if (defender == NULL)
+        return (0);
 
     if (defender->type == MONS_BLINK_FROG
         || defender->type == MONS_PRINCE_RIBBIT
@@ -1158,17 +1142,16 @@ static int _intoxicate_monsters(coord_def where, int pow, int, actor *)
 {
     UNUSED( pow );
 
-    int mon = mgrd(where);
-
-    if (mon == NON_MONSTER
-        || mons_intel(&menv[mon]) < I_NORMAL
-        || mons_holiness(&menv[mon]) != MH_NATURAL
-        || mons_res_poison(&menv[mon]) > 0)
+    monsters *monster = monster_at(where);
+    if (monster == NULL
+        || mons_intel(monster) < I_NORMAL
+        || mons_holiness(monster) != MH_NATURAL
+        || mons_res_poison(monster) > 0)
     {
         return 0;
     }
 
-    menv[mon].add_ench(mon_enchant(ENCH_CONFUSION, 0, KC_YOU));
+    monster->add_ench(mon_enchant(ENCH_CONFUSION, 0, KC_YOU));
     return 1;
 }
 
@@ -1191,38 +1174,37 @@ bool backlight_monsters(coord_def where, int pow, int garbage)
     UNUSED( pow );
     UNUSED( garbage );
 
-    int mon = mgrd(where);
-
-    if (mon == NON_MONSTER)
+    monsters *monster = monster_at(where);
+    if (monster == NULL)
         return (false);
 
     // Already glowing.
-    if (mons_class_flag(menv[mon].type, M_GLOWS))
+    if (mons_class_flag(monster->type, M_GLOWS))
         return (false);
 
-    mon_enchant bklt = menv[mon].get_ench(ENCH_BACKLIGHT);
+    mon_enchant bklt = monster->get_ench(ENCH_BACKLIGHT);
     const int lvl = bklt.degree;
 
     // This enchantment overrides invisibility (neat).
-    if (menv[mon].has_ench(ENCH_INVIS))
+    if (monster->has_ench(ENCH_INVIS))
     {
-        if (!menv[mon].has_ench(ENCH_BACKLIGHT))
+        if (!monster->has_ench(ENCH_BACKLIGHT))
         {
-            menv[mon].add_ench(
+            monster->add_ench(
                 mon_enchant(ENCH_BACKLIGHT, 1, KC_OTHER, random_range(30, 50)));
-            simple_monster_message( &menv[mon], " is lined in light." );
+            simple_monster_message(monster, " is lined in light.");
         }
         return (true);
     }
 
-    menv[mon].add_ench(mon_enchant(ENCH_BACKLIGHT, 1));
+    monster->add_ench(mon_enchant(ENCH_BACKLIGHT, 1));
 
     if (lvl == 0)
-        simple_monster_message( &menv[mon], " is outlined in light." );
+        simple_monster_message(monster, " is outlined in light.");
     else if (lvl == 4)
-        simple_monster_message( &menv[mon], " glows brighter for a moment." );
+        simple_monster_message(monster, " glows brighter for a moment.");
     else
-        simple_monster_message( &menv[mon], " glows brighter." );
+        simple_monster_message(monster, " glows brighter.");
 
     return (true);
 }
@@ -1524,39 +1506,36 @@ void cast_fulsome_distillation( int powc )
 
 static int _rot_living(coord_def where, int pow, int, actor *)
 {
-    const int mon = mgrd(where);
-    int ench;
-
-    if (mon == NON_MONSTER)
-        return 0;
+    monsters *monster = monster_at(where);
+    if (monster == NULL)
+        return (0);
 
-    if (mons_holiness(&menv[mon]) != MH_NATURAL)
-        return 0;
+    if (mons_holiness(monster) != MH_NATURAL)
+        return (0);
 
-    if (check_mons_resist_magic(&menv[mon], pow))
-        return 0;
+    if (check_mons_resist_magic(monster, pow))
+        return (0);
 
-    ench = ((random2(pow) + random2(pow) + random2(pow) + random2(pow)) / 4);
+    int ench = ((random2(pow) + random2(pow) + random2(pow) + random2(pow))/4);
     ench = 1 + (ench >= 20) + (ench >= 35) + (ench >= 50);
 
-    menv[mon].add_ench( mon_enchant(ENCH_ROT, ench, KC_YOU) );
+    monster->add_ench(mon_enchant(ENCH_ROT, ench, KC_YOU));
 
-    return 1;
+    return (1);
 }
 
 static int _rot_undead(coord_def where, int pow, int, actor *)
 {
-    const int mon = mgrd(where);
-    int ench;
+    monsters *monster = monster_at(where);
 
-    if (mon == NON_MONSTER)
-        return 0;
+    if (monster == NULL)
+        return (0);
 
-    if (mons_holiness(&menv[mon]) != MH_UNDEAD)
-        return 0;
+    if (mons_holiness(monster) != MH_UNDEAD)
+        return (0);
 
-    if (check_mons_resist_magic(&menv[mon], pow))
-        return 0;
+    if (check_mons_resist_magic(monster, pow))
+        return (0);
 
     // This does not make sense -- player mummies are
     // immune to rotting (or have been) -- so what is
@@ -1569,7 +1548,7 @@ static int _rot_undead(coord_def where, int pow, int, actor *)
     //     insist that monsters get the same treatment as
     //     players, I demand my player mummies get to worship
     //     the evil mummy & orc gods.
-    switch (menv[mon].type)
+    switch (monster->type)
     {
     case MONS_ZOMBIE_SMALL:
     case MONS_ZOMBIE_LARGE:
@@ -1592,12 +1571,12 @@ static int _rot_undead(coord_def where, int pow, int, actor *)
         return 0;               // Immune (no flesh) or already rotting.
     }
 
-    ench = ((random2(pow) + random2(pow) + random2(pow) + random2(pow)) / 4);
+    int ench = ((random2(pow) + random2(pow) + random2(pow) + random2(pow))/4);
     ench = 1 + (ench >= 20) + (ench >= 35) + (ench >= 50);
 
-    menv[mon].add_ench( mon_enchant(ENCH_ROT, ench, KC_YOU) );
+    monster->add_ench(mon_enchant(ENCH_ROT, ench, KC_YOU));
 
-    return 1;
+    return (1);
 }
 
 static int _rot_corpses(coord_def where, int pow, int, actor *)
@@ -1624,24 +1603,23 @@ void do_monster_rot(int mon)
     }
 
     _player_hurt_monster( mon, damage );
-    return;
 }
 
 static int _snake_charm_monsters(coord_def where, int pow, int, actor *)
 {
-    const int mon = mgrd(where);
+    monsters* monster = monster_at(where);
 
-    if (mon == NON_MONSTER
+    if (monster == NULL
         || one_chance_in(4)
-        || mons_friendly(&menv[mon])
-        || mons_char(menv[mon].type) != 'S'
-        || check_mons_resist_magic(&menv[mon], pow))
+        || mons_friendly(monster)
+        || mons_char(monster->type) != 'S'
+        || check_mons_resist_magic(monster, pow))
     {
         return 0;
     }
 
-    menv[mon].attitude = ATT_FRIENDLY;
-    mprf("%s sways back and forth.", menv[mon].name(DESC_CAP_THE).c_str());
+    monster->attitude = ATT_FRIENDLY;
+    mprf("%s sways back and forth.", monster->name(DESC_CAP_THE).c_str());
 
     return 1;
 }
@@ -2009,8 +1987,10 @@ bool cast_fragmentation(int pow, const dist& spd)
 
 bool cast_twist(int pow, const coord_def& where)
 {
+    monsters *monster = monster_at(where);
+
     // Anything there?
-    if (invalid_monster_index(mgrd(where)))
+    if (monster == NULL)
     {
         mpr("There is no monster there!");
         // This counts as a real cast, in order not to leak invisible
@@ -2018,16 +1998,14 @@ bool cast_twist(int pow, const coord_def& where)
         return (true);
     }
 
-    monsters& m = menv[mgrd(where)];
-
     // Identify mimics, if necessary.
-    if (mons_is_mimic(m.type))
-        m.flags |= MF_KNOWN_MIMIC;
+    if (mons_is_mimic(monster->type))
+        monster->flags |= MF_KNOWN_MIMIC;
 
     // Monster can magically save vs attack.
-    if (check_mons_resist_magic(&m, pow * 2))
+    if (check_mons_resist_magic(monster, pow * 2))
     {
-        simple_monster_message(&m, mons_resist_string(&m));
+        simple_monster_message(monster, mons_resist_string(monster));
         return (true);
     }
 
@@ -2038,10 +2016,9 @@ bool cast_twist(int pow, const coord_def& where)
     const int damage = 1 + random2(3 + pow / 5);
 
     // Inflict the damage.
-    _player_hurt_monster(m, damage);
-
-    if (mons_is_mimic(m.type))
-        mimic_alert(&m);
+    if (!_player_hurt_monster(*monster, damage))
+        if (mons_is_mimic(monster->type))
+            mimic_alert(monster);
 
     return (true);
 }
@@ -2100,7 +2077,7 @@ void cast_far_strike(int pow)
         return;
 
     // Get the target monster...
-    if (mgrd(targ.target) == NON_MONSTER || targ.isMe)
+    if (monster_at(targ.target) == NULL)
     {
         mpr("There is no monster there!");
         return;
@@ -2173,8 +2150,7 @@ void cast_far_strike(int pow)
     damage *= dammod;
     damage /= 78;
 
-    const int midx = mgrd(targ.target);
-    monsters *monster = &menv[midx];
+    monsters *monster = monster_at(targ.target);
 
     // Apply monster's AC.
     if (monster->ac > 0)
@@ -2193,7 +2169,7 @@ void cast_far_strike(int pow)
     }
 
     // Inflict the damage.
-    _player_hurt_monster(midx, damage);
+    _player_hurt_monster(*monster, damage);
 }
 
 bool cast_apportation(int pow, const coord_def& where)
@@ -2216,15 +2192,13 @@ bool cast_apportation(int pow, const coord_def& where)
     if (item_idx == NON_ITEM)
     {
         // Maybe the player *thought* there was something there (a mimic.)
-        const int mon = mgrd(where);
-        if (!invalid_monster_index(mon))
+        if (monsters* m = monster_at(where))
         {
-            monsters& m = menv[mon];
-            if (mons_is_mimic(m.type) && you.can_see(&m))
+            if (mons_is_mimic(m->type) && you.can_see(m))
             {
-                mprf("%s twitches.", m.name(DESC_CAP_THE).c_str());
+                mprf("%s twitches.", m->name(DESC_CAP_THE).c_str());
                 // Nothing else gives this message, so identify the mimic.
-                m.flags |= MF_KNOWN_MIMIC;
+                m->flags |= MF_KNOWN_MIMIC;
                 return (true);  // otherwise you get free mimic ID
             }
         }
@@ -2267,10 +2241,8 @@ bool cast_apportation(int pow, const coord_def& where)
         && item_is_stationary(item))
     {
         remove_item_stationary(item);
-
-        const int mon = mgrd(where);
-        if (!invalid_monster_index(mon))
-            menv[mon].del_ench(ENCH_HELD, true);
+        if (monsters *monster = monster_at(where))
+            monster->del_ench(ENCH_HELD, true);
     }
 
     // Actually move the item.
diff --git a/crawl-ref/source/spl-util.cc b/crawl-ref/source/spl-util.cc
index 9886c334fa..4f892d6f4e 100644
--- a/crawl-ref/source/spl-util.cc
+++ b/crawl-ref/source/spl-util.cc
@@ -529,7 +529,7 @@ int apply_random_around_square(cell_func cf, const coord_def& where,
 
     for (adjacent_iterator ai(where, exclude_center); ai; ++ai)
     {
-        if (mgrd(*ai) == NON_MONSTER && *ai != you.pos())
+        if (monster_at(*ai) == NULL && *ai != you.pos())
             continue;
 
         // Found target
diff --git a/crawl-ref/source/stuff.cc b/crawl-ref/source/stuff.cc
index b4a86f9614..22726b562f 100644
--- a/crawl-ref/source/stuff.cc
+++ b/crawl-ref/source/stuff.cc
@@ -343,11 +343,10 @@ static bool _tag_follower_at(const coord_def &pos)
     if (!in_bounds(pos) || pos == you.pos())
         return (false);
 
-    if (mgrd(pos) == NON_MONSTER)
+    monsters *fmenv = monster_at(pos);
+    if (fmenv == NULL)
         return (false);
 
-    monsters *fmenv = &menv[mgrd(pos)];
-
     if (fmenv->type == MONS_PLAYER_GHOST
         || !fmenv->alive()
         || fmenv->incapacitated()
@@ -1657,8 +1656,6 @@ void zap_los_monsters()
         if (g == you.pos())
             continue;
 
-        int imon = mgrd(g);
-
         // At tutorial beginning disallow items in line of sight.
         if (Options.tutorial_events[TUT_SEEN_FIRST_OBJECT])
         {
@@ -1668,12 +1665,11 @@ void zap_los_monsters()
                 destroy_item(item);
         }
 
-        if (imon == NON_MONSTER || imon == MHITYOU)
-            continue;
-
         // If we ever allow starting with a friendly monster,
         // we'll have to check here.
-        monsters *mon = &menv[imon];
+        monsters *mon = monster_at(g);
+        if (mon == NULL)
+            continue;
 
         if (mons_class_flag( mon->type, M_NO_EXP_GAIN ))
             continue;
diff --git a/crawl-ref/source/travel.cc b/crawl-ref/source/travel.cc
index caba8bb6ce..584e6c5e63 100644
--- a/crawl-ref/source/travel.cc
+++ b/crawl-ref/source/travel.cc
@@ -844,14 +844,12 @@ inline static void _check_interesting_square(int x, int y,
 
     if (ES_item || ES_greedy || ES_glow || ES_art || ES_rune)
     {
-        if (mgrd(pos) != NON_MONSTER)
+        if (const monsters *mons = monster_at(pos))
         {
-            const monsters *mons = &menv[ mgrd(pos) ];
             if (mons_is_mimic(mons->type) && !mons_is_known_mimic(mons))
             {
                 item_def item;
                 get_mimic_item(mons, item);
-
                 ed.found_item(pos, item);
             }
         }
@@ -1416,10 +1414,8 @@ static bool _is_greed_inducing_square(const LevelStashes *ls,
     if (ls && ls->needs_visit(c.x, c.y))
         return (true);
 
-    const int m_ind = mgrd(c);
-    if (m_ind != NON_MONSTER)
+    if (const monsters *mons = monster_at(c))
     {
-        const monsters *mons = &menv[ m_ind ];
         if (mons_is_mimic(mons->type)
             && mons_was_seen(mons)
             && !mons_is_known_mimic(mons))
@@ -4028,7 +4024,7 @@ bool runrest::run_grids_changed() const
     if (env.cgrid(you.pos() + pos) != EMPTY_CLOUD)
         return (true);
 
-    if (mgrd(you.pos() + pos) != NON_MONSTER)
+    if (monster_at(you.pos() + pos))
         return (true);
 
     for (int i = 0; i < 3; i++)
diff --git a/crawl-ref/source/tutorial.cc b/crawl-ref/source/tutorial.cc
index d12e781346..027635cae1 100644
--- a/crawl-ref/source/tutorial.cc
+++ b/crawl-ref/source/tutorial.cc
@@ -1313,7 +1313,7 @@ void tutorial_first_monster(const monsters &mon)
 void tutorial_first_item(const item_def &item)
 {
     // Happens if monster is standing on dropped corpse or item.
-    if (mgrd(item.pos) != NON_MONSTER)
+    if (monster_at(item.pos))
         return;
 
     if (!Options.tutorial_events[TUT_SEEN_FIRST_OBJECT]
@@ -1323,7 +1323,7 @@ void tutorial_first_item(const item_def &item)
         // corpse, TUT_SEEN_CARRION is done when a corpse is first seen.
         if (!Options.tut_just_triggered
             && item.base_type == OBJ_CORPSES
-            && mgrd(item.pos) == NON_MONSTER)
+            && monster_at(item.pos) == NULL)
         {
             learned_something_new(TUT_SEEN_CARRION, item.pos);
         }
@@ -1783,7 +1783,7 @@ void learned_something_new(tutorial_event_type seen_what, coord_def gc)
         text << "These ";
 #ifndef USE_TILE
         // Is a monster blocking the view?
-        if (mgrd(gc) != NON_MONSTER)
+        if (monster_at(gc))
             DELAY_EVENT;
 
         object = env.show(e);
@@ -1811,7 +1811,7 @@ void learned_something_new(tutorial_event_type seen_what, coord_def gc)
             DELAY_EVENT;
 
         // monsters standing on stairs
-        if (mgrd(gc) != NON_MONSTER)
+        if (monster_at(gc))
             DELAY_EVENT;
 
         text << "These ";
@@ -1840,7 +1840,7 @@ void learned_something_new(tutorial_event_type seen_what, coord_def gc)
         text << "This ";
 #ifndef USE_TILE
         // Is a monster blocking the view?
-        if (mgrd(gc) != NON_MONSTER)
+        if (monster_at(gc))
             DELAY_EVENT;
 
         // FIXME: Branch entrance character is not being colored yellow.
@@ -1873,7 +1873,7 @@ void learned_something_new(tutorial_event_type seen_what, coord_def gc)
         return;
 #else
         // Monster or player standing on stairs.
-        if (mgrd(gc) != NON_MONSTER || (you.pos() == gc))
+        if (monster_at(gc) || (you.pos() == gc))
             DELAY_EVENT;
 
         text << "If any items are covering stairs or an escape hatch then "
@@ -2643,11 +2643,8 @@ void learned_something_new(tutorial_event_type seen_what, coord_def gc)
     case TUT_MONSTER_BRAND:
 #ifdef USE_TILE
         tiles.place_cursor(CURSOR_TUTORIAL, gc);
-        if (mgrd(gc) != NON_MONSTER)
-        {
-            tiles.add_text_tag(TAG_TUTORIAL, menv[mgrd(gc)].name(DESC_CAP_A),
-                               gc);
-        }
+        if (const monsters *m = monster_at(gc))
+            tiles.add_text_tag(TAG_TUTORIAL, m->name(DESC_CAP_A), gc);
 #endif
         text << "That monster looks a bit unusual. You might wish to examine "
                 "it a bit more closely by "
@@ -2661,11 +2658,8 @@ void learned_something_new(tutorial_event_type seen_what, coord_def gc)
     case TUT_MONSTER_FRIENDLY:
 #ifdef USE_TILE
         tiles.place_cursor(CURSOR_TUTORIAL, gc);
-        if (mgrd(gc) != NON_MONSTER)
-        {
-            tiles.add_text_tag(TAG_TUTORIAL, menv[mgrd(gc)].name(DESC_CAP_A),
-                               gc);
-        }
+        if (const monsters *m = monster_at(gc))
+            tiles.add_text_tag(TAG_TUTORIAL, m->name(DESC_CAP_A), gc);
 #endif
         text << "That monster is friendly to you and will attack your "
                 "enemies, though you'll get only half the experience for "
@@ -3812,15 +3806,11 @@ static void _tutorial_describe_disturbance(int x, int y)
 
 static bool _water_is_disturbed(int x, int y)
 {
-    int mon_num = mgrd[x][y];
+    const coord_def c(x,y);
+    const monsters *mon = monster_at(c);
 
-    if (mon_num == NON_MONSTER || grd[x][y] != DNGN_SHALLOW_WATER
-        || !see_grid(x, y))
-    {
+    if (mon == NULL || grd(c) != DNGN_SHALLOW_WATER || !see_grid(c))
         return (false);
-    }
-
-    const monsters *mon = &menv[mon_num];
 
     return (!player_monster_visible(mon) && !mons_flies(mon));
 }