Returns the result of applying a callback to each value

# Ds\Map::map

(PECL ds >= 1.0.0)

Ds\Map::map — Returns the result of applying a callback to each value

### 说明

public function Ds\Map::map(callable `$callback`): Ds\Map

Returns the result of applying a `callback` function to each value of the map.

### 参数

`callback`

  function callback(mixed `$key`, mixed `$value`): mixed

  A callable to apply to each value in the map.

  The callable should return what the key will be mapped to in the resulting map.

### 返回值

The result of applying a `callback` to each value in the map.

> 注意:

> The keys and values of the current instance won't be affected.

### 示例

示例 #1 Ds\Map::map() example

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

    print_r($map->map(function($key, $value) { return $value * 2; }));
    print_r($map);
    ?>

以上示例的输出类似于：

    (
        [0] => Ds\Pair Object
            (
                [key] => a
                [value] => 2
            )

        [1] => Ds\Pair Object
            (
                [key] => b
                [value] => 4
            )

        [2] => Ds\Pair Object
            (
                [key] => c
                [value] => 6
            )

    )
    Ds\Map Object
    (
        [0] => Ds\Pair Object
            (
                [key] => a
                [value] => 1
            )

        [1] => Ds\Pair Object
            (
                [key] => b
                [value] => 2
            )

        [2] => Ds\Pair Object
            (
                [key] => c
                [value] => 3
            )

    )

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