Understanding PHP's array_key_first() Function: Syntax, Usage, and Examples

PHP 7.3 added a new array function called array_key_first(), which returns the first key name of an array. This article explores the function's syntax, behavior, and typical use cases.

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

Usage Scenarios

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 whether an array is empty

Previously, empty() or count() were used to check for an empty array. The array_key_first() function can achieve the same check more concisely.

$arr = [];

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

Result Array is empty Note: If the array contains elements whose value is null, using array_key_first() may lead to unexpected results, so extra caution is required.

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 if an array is empty. When using it, be aware of edge cases where array elements have null values.