array_key_first

(PHP 7 >= 7.3.0, PHP 8)

array_key_first — Gets the first key of an array

Descrizione

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

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

Elenco dei parametri

array: An array.

Valori restituiti

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

Esempi

Example #1 Basic array_key_first() Usage

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

$firstKey = array_key_first($array);

var_dump($firstKey);
?>

Il precedente esempio visualizzerà:

string(1) "a"

Note

Suggerimento

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;
    }
}
?>

Vedere anche:

array_key_last() - Gets the last key of an array
reset() - Reimposta il puntatore interno di un array sulla posizione iniziale

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User Contributed Notes 2 notes

down

MaxiCom dot Developpement at gmail dot com ¶

4 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));

?>

down

-20

Anonymous ¶

8 months ago

The best way to polyfill array_key_first is:



$first_key = array_keys($array)[0] ?? NULL;

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