# 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()`.

```php
// 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.

```php
$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.

```php
// 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.

```php
$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"
```

[[programming/php/php]] [[programming/php/php-operators]]