Understanding PHP’s array_key_first() Function: Syntax, Examples, and Use Cases

In PHP 7.3, a new array function array_key_first() was added. This function returns the first key name of an array, or null if the array is empty.

Syntax

array_key_first (array $array) : mixed

Description

The array_key_first() function accepts an array argument and returns the value of its first key. If the array is empty, it returns null .

Example 1

$arr = ['a' => 1, 'b' => 2, 'c' => 3];

echo array_key_first($arr); // outputs a

Example 2

$arr = [];

echo array_key_first($arr); // outputs null

Use Cases

1. Retrieve the first element’s key name

Before PHP 7.3, developers often used reset() to get the first element’s value and then key() to obtain its key. Using array_key_first() simplifies this process.

$arr = ['a' => 1, 'b' => 2, 'c' => 3];

echo array_key_first($arr); // outputs a

2. Determine if an array is empty

Previously, empty() or count() were used to check emptiness. array_key_first() can achieve the same check more concisely.

$arr = [];

if (array_key_first($arr) === null) {
    echo 'Array is empty';
}

Result

Array is empty

Note: If an array contains an element with a null value, using array_key_first() may lead to unexpected results.

Summary

The array_key_first() function, introduced in PHP 7.3, provides a convenient way to obtain the first key of an array and can also be used to check whether an array is empty, though care is needed when the array includes null values.

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