offsetexists

WeakMap::offsetExists
Checks whether a certain object is in the map
ENTITY
public
bool
WeakMap::offsetExists
object
object
Checks whether the passed object is referenced in the map.
ENTITY
object
Object to check for.
ENTITY
Returns ENTITY if the object is contained in the map, ENTITY otherwise.
ENTITY
[!NOTE]
Like 
isset, this method returns ENTITY if the value associated with 
object is ENTITY, even though the object is still contained in the map.