(PECL weakref >= 0.2.0) Counts the number of live entries in the map

(PECL weakref >= 0.2.0) Checks whether a certain object is in the map

(PECL weakref >= 0.2.0) Returns the current key under iteration.

(PECL weakref >= 0.2.0) Constructs a new map

(PECL weakref >= 0.1.0) Returns the object pointed to by the weak reference

(PECL weakref >= 0.2.0) Removes an entry from the map