Master PHP 7.3’s array_key_first(): Retrieve the First Array Key Effortlessly

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

Syntax

array_key_first (array $array) : mixed

Description

The function accepts a single array argument and returns the value of its first key. If the array contains no elements, it returns null.

Example 1 – Basic Usage

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

echo array_key_first($arr); // outputs a

Example 2 – Empty Array

$arr = [];

echo array_key_first($arr); // outputs null

Use Cases

1. Retrieve the first element’s key

Before PHP 7.3, developers often combined reset() to get the first value and key() to obtain its key. array_key_first() simplifies this to a single call.

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

echo array_key_first($arr); // outputs a

2. Determine if an array is empty

Older code used empty() or count(). With array_key_first(), you can check for emptiness directly:

$arr = [];

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

Output:

数组为空

Important Note

If an array contains an element whose value is null, using array_key_first() may lead to unexpected results, so extra caution is required.

Conclusion

The array_key_first() function provides a concise way to obtain the first key of an array and to check for an empty array in PHP 7.3+, but developers should be aware of the edge case when null values are present.