Returns the result of applying a callback to each value

# Ds\Deque::map

(PECL ds >= 1.0.0)

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

### 说明

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

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

### 参数

`callback`

  function callback(mixed `$value`): mixed

  A callable to apply to each value in the deque.

  The callable should return what the new value will be in the new deque.

### 返回值

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

> 注意:

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

### 示例

示例 #1 Ds\Deque::map() example

    <?php
    $deque = new \Ds\Deque([1, 2, 3]);

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

以上示例的输出类似于：

    Ds\Deque Object
    (
        [0] => 2
        [1] => 4
        [2] => 6
    )
    Ds\Deque Object
    (
        [0] => 1
        [1] => 2
        [2] => 3
    )

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