Null Coalescing Operator Not Used

Also Known As

TL;DR

Explanation

PHP 7.0 introduced ?? which returns the left operand if it exists and is not null, otherwise the right. PHP 7.4 added ??= which assigns only if the variable is null. These replace the common isset($x) ? $x : $default pattern. The operator also works on array keys and chained access: $config['db']['host'] ?? 'localhost'. Unlike the ternary shorthand (?:), null coalescing does not trigger a notice for undefined variables.

Common Misconception

Why It Matters

Common Mistakes

• Using isset($x) ? $x : $default when $x ?? $default is available (PHP 7+).
• if (!isset($arr[$key])) $arr[$key] = []; — use $arr[$key] ??= [].
• Using ?: which triggers notices for undefined variables instead of ??.
• Forgetting ?? works on chained array access: $data['user']['name'] ?? 'Unknown'.

Code Examples

// Verbose — pre-PHP 7 style:
$name    = isset($_GET['name']) ? $_GET['name'] : 'Guest';
$timeout = isset($config['timeout']) ? $config['timeout'] : 30;
$locale  = isset($user) && isset($user->locale) ? $user->locale : 'en';

// Assignment:
if (!isset($cache[$key])) {
    $cache[$key] = [];
}

// Clean — null coalescing:
$name    = $_GET['name']       ?? 'Guest';
$timeout = $config['timeout']  ?? 30;
$locale  = $user?->locale      ?? 'en';

// Null coalescing assignment:
$cache[$key] ??= [];

// Chained:
$value = $request->get('x') ?? $config['x'] ?? $defaults['x'] ?? null;

References

• ↗ https://www.php.net/manual/en/migration70.new-features.php#migration70.new-features.null-coalesce-op

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