PHP マニュアル: Creates a new map using keys that aren't in another map

public Ds\Map Ds\Map::diff(Ds\Map $map)

Returns the result of removing all keys from the current instance that are present in a given map.

A \ B = {x ∈ A | x ∉ B}

The result of removing all keys from the current instance that are present in a given map.

例1 Ds\Map::diff example

<?php
$a = new \Ds\Map(["a" => 1, "b" => 2, "c" => 3]);
$b = new \Ds\Map(["b" => 4, "c" => 5, "d" => 6]);

var_dump($a->diff($b));
?>

上の例の出力は、たとえば以下のようになります。

object(Ds\Map)#3 (1) {
  [0]=>
  object(Ds\Pair)#4 (2) {
    ["key"]=>
    string(1) "a"
    ["value"]=>
    int(1)
  }
}