Ds\Deque
PHP マニュアル

Ds\Deque::reduce

Reduces the deque to a single value using a callback function

説明

public mixed Ds\Deque::reduce(callable $callback, mixed $initial = ?)

Reduces the deque to a single value using a callback function.

パラメータ

callback
mixed callback(mixed $carry, mixed $value)
carry

The return value of the previous callback, or initial if it's the first iteration.

value

The value of the current iteration.

initial

The initial value of the carry value. Can be null.

戻り値

The return value of the final callback.

例

例1 Ds\Deque::reduce with initial value example

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

$callback = function($carry, $value) {
    return $carry * $value;
};

var_dump($deque->reduce($callback, 5));

// Iterations:
//
// $carry = $initial = 5
//
// $carry = $carry * 1 =  5
// $carry = $carry * 2 = 10
// $carry = $carry * 3 = 30
?>

上の例の出力は、 たとえば以下のようになります。

int(30)

例2 Ds\Deque::reduce without an initial value example

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

var_dump($deque->reduce(function($carry, $value) {
    return $carry + $value + 5;
}));

// Iterations:
//
// $carry = $initial = null
//
// $carry = $carry + 1 + 5 =  6
// $carry = $carry + 2 + 5 = 13
// $carry = $carry + 3 + 5 = 21
?>

上の例の出力は、 たとえば以下のようになります。

int(21)