Understanding PHP 7.3 array_key_first() Function: Syntax, Usage, and Examples

PHP 7.3 added the array_key_first() function, which returns the first key of an array or null when the array is empty.

Syntax

array_key_first (array $array) : mixed

Description

The function accepts an array argument and returns the value of its first key; if the array is empty it returns null.

Examples

Example 1:

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

echo array_key_first($arr); // 输出a

Example 2:

$arr = [];

echo array_key_first($arr); // 输出null

Use Cases

1. Retrieve the first element's key

Before PHP 7.3 developers often used reset() to get the first value and key() to get its key; array_key_first() simplifies this process.

Example:

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

echo array_key_first($arr); // 输出a

2. Determine if an array is empty

Instead of empty() or count(), array_key_first() can be used to check emptiness more directly.

Example:

$arr = [];

if (array_key_first($arr) === null) {
    echo '数组为空';
}

Result:

数组为空

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 test whether an array is empty; however, developers should be cautious when the array contains elements with null values.