array_key_first

(PHP 7 >= 7.3.0, PHP 8)

array_key_first — Gets the first key of an array

Опис

array_key_first(array $array): int|string|null

Get the first key of the given array without affecting the internal array pointer.

Параметри

array: An array.

Значення, що повертаються

Returns the first key of array if the array is not empty; null otherwise.

Приклади

Приклад #1 Basic array_key_first() Usage

<?php
$array = ['a' => 1, 'b' => 2, 'c' => 3];

$firstKey = array_key_first($array);

var_dump($firstKey);
?>

Поданий вище приклад виведе:

string(1) "a"

Примітки

Підказка

There are several ways to provide this functionality for versions prior to PHP 7.3.0. It is possible to use array_keys(), but that may be rather inefficient. It is also possible to use reset() and key(), but that may change the internal array pointer. An efficient solution, which does not change the internal array pointer, written as polyfill:

<?php
if (!function_exists('array_key_first')) {
    function array_key_first(array $arr) {
        foreach($arr as $key => $unused) {
            return $key;
        }
        return NULL;
    }
}
?>

Прогляньте також

array_key_last() - Gets the last key of an array
reset() - Встановлює внутрішній вказівних масиву на його перший елемент

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User Contributed Notes 1 note

down

MaxiCom dot Developpement at gmail dot com ¶

10 months ago

A polyfill serves the purpose of retroactively incorporating new features from PHP releases into older PHP versions, ensuring API compatibility.

In PHP 7.3.0, the array_key_first() function was introduced, demonstrated in the following example:

<?php

$array = [
    'first_key' => 'first_value',
    'second_key' => 'second_value',
];

var_dump(array_key_first($array));

?>

The provided polyfill in this documentation allows the convenient use of array_key_first() with API compatibility in PHP versions preceding PHP 7.3.0, where the function was not implemented:

<?php

if (!function_exists('array_key_first')) {
    function array_key_first(array $arr) {
        foreach ($arr as $key => $unused) {
            return $key;
        }
        return null;
    }
}

$array = [
    'first_key' => 'first_value',
    'second_key' => 'second_value',
];

var_dump(array_key_first($array));

?>

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