Rework mon-pick algorithm as a class template

This enables the distributions to be easily used for picking over
enums other than monster_type, and even for arbitrary objects.

The new template is contained in random_pick. It can be used
simply by creating a random_picker<T> and calling its pick
method, or can be subclassed if more complex veto behaviour
is required.

1 files changed, 21 insertions, 19 deletions

diff --git a/crawl-ref/source/mon-pick.h b/crawl-ref/source/mon-pick.h
index 47ddce1755..7ad9154a7f 100644
--- a/crawl-ref/source/mon-pick.h
+++ b/crawl-ref/source/mon-pick.h
@@ -8,27 +8,11 @@
 #define MONPICK_H
 
 #include "externs.h"
+#include "random-pick.h"
 
 #define DEPTH_NOWHERE 999
 
-enum distrib_type
-{
-    FLAT, // full chance throughout the range
-    SEMI, // 50% chance at range ends, 100% in the middle
-    PEAK, // 0% chance just outside range ends, 100% in the middle, range
-          // ends typically get ~20% or more
-    UP,   // linearly from near-zero to 100%, increasing with depth
-    DOWN, // linearly from 100% at the start to near-zero
-};
-
-typedef struct
-{
-    int minr;
-    int maxr;
-    int rarity; // 0..1000
-    distrib_type distrib;
-    monster_type mons;
-} pop_entry;
+#define pop_entry random_pick_entry<monster_type>
 
 typedef bool (*mon_pick_vetoer)(monster_type);
 
@@ -36,7 +20,8 @@ int mons_rarity(monster_type mcls, branch_type branch);
 int mons_depth(monster_type mcls, branch_type branch);
 
 monster_type pick_monster(level_id place, mon_pick_vetoer veto = nullptr);
-monster_type pick_monster_from(const pop_entry *fpop, int depth, mon_pick_vetoer veto = nullptr);
+monster_type pick_monster_from(const pop_entry *fpop, int depth,
+                               mon_pick_vetoer = nullptr);
 monster_type pick_monster_no_rarity(branch_type branch);
 monster_type pick_monster_by_hash(branch_type branch, uint32_t hash);
 monster_type pick_monster_all_branches(int absdepth0, mon_pick_vetoer veto = nullptr);
@@ -44,4 +29,21 @@ bool branch_has_monsters(branch_type branch);
 int branch_ood_cap(branch_type branch);
 
 void debug_monpick();
+
+// Subclass the random_picker template to make a monster_picker class.
+// The main reason for this is that passing delegates into template functions
+// is fraught with peril when the delegate's arguments use T, until 0x at least.
+// There is supposedly a nasty workaround but this wouldn't even compile for me.
+class monster_picker : public random_picker<monster_type, NUM_MONSTERS>
+{
+public:
+    monster_picker(mon_pick_vetoer vetoer = nullptr) : _veto(vetoer) { };
+
+protected:
+    virtual bool veto(monster_type mon);
+
+private:
+    mon_pick_vetoer _veto;
+};
+
 #endif