Question

read变量的值如何来自$item

$products

Answer 1

如果您深入了解laravel框架，$products的类型为Illuminate\Database\Eloquent\Collection。它实现了map方法，underlying implementation是：

public function map(callable $callback)
{
    $result = parent::map($callback);
    return $result->contains(function ($item) {
        return ! $item instanceof Model;
    }) ? $result->toBase() : $result;
}

Illuminate\Database\Eloquent\Collection的父类是Illuminate\Support\Collection，而underlying implementation是：

public function map(callable $callback)
{
    $keys = array_keys($this->items);
    $items = array_map($callback, $this->items, $keys);
    return new static(array_combine($keys, $items));
}

它使用array_map方法，它会将回调函数应用于每个值。

array array_map ( callable $callback , array $array1 [, array $... ] )

Answer 2

一个简单的例子，向您展示如何实现它 https://implode.io/Ce1azD

class Products
{
    protected $items = [];

    public function __construct($items)
    {
        $this->items = $items;
    }

    public function map(callable $callback)
    {
        return array_map($callback, $this->items);
    }
}

$products = new Products([1, 2, 3, 4]);

return $products->map(function ($item) {
    return $item * 2;
});

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2 个答案: