PHP Null Coalescing Operator (??)
The null coalescing operator ?? was introduced in PHP 7. It is used to return the first operand if it exists and is not null; otherwise, it returns the second operand.
1. Basic Usage
It is essentially syntactic sugar for the common case of needing to use a ternary in conjunction with isset().
// Old way
$username = isset($_GET['user']) ? $_GET['user'] : 'nobody';
// New way with ??
$username = $_GET['user'] ?? 'nobody';2. Chaining
You can chain the operators. The first defined value (reading from left to right) will be returned.
$val = $input ?? $default ?? "fallback";3. Null Coalescing Assignment (??=)
Introduced in PHP 7.4, this operator assigns a value to a variable only if that variable is currently null.
// Old way
if (!isset($username)) {
$username = 'Guest';
}
// New way
$username ??= 'Guest';4. Comparison with Ternary (?:)
The shorthand ternary operator ?: checks for truthiness, whereas ?? checks if the value is set and not null.
$a = false;
echo $a ?? "a is not set"; // Outputs: false (because $a is set, even if false)
echo $a ?: "a is false"; // Outputs: "a is false"