The Ds\Map::apply() function of the Map class in PHP is used to apply a specific operation to all of the elements present in the map. It accepts a callback function and updates all of the elements present in the Map according to the given callback function.
Syntax:
void public Ds\Map::apply ( callable $callback )
Note: The callback function should return the updated value for specific key-value pair.
Parameters: It accepts a callback function as a parameter and updates all of the elements according to that function.
Return value: This function does not returns any value.
Below programs illustrate the Ds\Map::apply() function in PHP:
Program 1:
<?php // PHP program to illustrate the apply() // function of Ds\map   // Creating a Map $map = new \Ds\Map(["1" => "Geeks",             "2" => "for", "3" => "Geeks"]);   // Converting all elements to uppercase // using callback function $map->apply(function($key, $value){                 return strtoupper($value);             });   print_r($map);   ?> |
Output:
Ds\Map Object
(
[0] => Ds\Pair Object
(
[key] => 1
[value] => GEEKS
)
[1] => Ds\Pair Object
(
[key] => 2
[value] => FOR
)
[2] => Ds\Pair Object
(
[key] => 3
[value] => GEEKS
)
)
Program 2:
<?php // PHP program to illustrate the apply() // function of Ds\map   // Creating a Map $map = new \Ds\Map(["1" => 5,             "2" => 10, "3" => 15]);   // Declare the callback function $callback = function($key, $value){                 return $value*10;             };               // Multiplying each value by 10 // using callback function $map->apply($callback);   print_r($map);   ?> |
Output:
Ds\Map Object
(
[0] => Ds\Pair Object
(
[key] => 1
[value] => 50
)
[1] => Ds\Pair Object
(
[key] => 2
[value] => 100
)
[2] => Ds\Pair Object
(
[key] => 3
[value] => 150
)
)
