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#ifndef UNWIND_H
#define UNWIND_H
/** Type that gives an lvalue dynamically-scoped temporary value. An
* unwind_var remembers the old value of a variable or other writable lvalue,
* and restores the original (or a specified) value when the unwind_var goes
* out of scope or is otherwise destroyed.
*/
template <typename T>
class unwind_var
{
public:
/** Wrap the lvalue val_ and on unwinding restore its original value. */
unwind_var(T &val_) : val(val_), oldval(val_) { }
/** Wrap the lvalue val_, assign it the temporary value newval, and
* on unwinding restore its original value.
*/
unwind_var(T &val_, T newval) : val(val_), oldval(val_)
{
val = newval;
}
/** Wrap the lvalue val_, assign it the temporary value newval, and
* on unwinding assign it the value reset_to.
*/
unwind_var(T &val_, T newval, T reset_to) : val(val_), oldval(reset_to)
{
val = newval;
}
~unwind_var()
{
val = oldval;
}
/** Get the current (temporary) value of the wrapped lvalue. */
T value() const
{
return val;
}
/** Get the value that will be used to restore the wrapped lvalue. */
T original_value() const
{
return oldval;
}
private:
T &val;
T oldval;
};
typedef unwind_var<bool> unwind_bool;
#endif
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