Returns a Map after an operation has been applied to each key and value in the current Map

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

Every key and value in the current Map 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 Map to the returned Map. The keys are only used to help in the mapping operation.


  • (function(Tk,Tv):Tu) $callback - The callback containing the operation to apply to the current Map keys and values.

Return Values

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