Returns an ImmMap after an operation has been applied to each key and value in current ImmMap

public function mapWithKey<Tu>(
  (function(Tk, Tv): Tu) $callback,
): ImmMap<Tk, Tu>;

Every key and value in the current ImmMap is affected by a call to mapWithKey(), unlike filterWithKey() where only values that meet a certain criteria are affected.

The keys will remain unchanged from the current ImmMap to the returned ImmMap. The keys are only used to help in the operation.


  • (function(Tk, Tv): Tu) $callback


  • ImmMap<Tk,Tu> - an ImmMap containing the values after a user-specified operation on the current ImmMap's keys and values is applied.


See [Map::mapWithKey](</hack/reference/class/Map/mapWithKey/#examples>) for usage examples.