What Is the Null Coalescing Operator in PHP?

Introduced in PHP 7, the null coalescing operator (??) has the following syntax:

// PHP 7+
leftExpr ?? rightExpr;

Which means that leftExpr is returned when leftExpr exists and is NOT null; otherwise it returns rightExpr. For example, all the following statements are equivalent:

// PHP 7+
// using the null coalescing operator
$x ?? $y;
// using the ternary operator
isset($x) ? $x : $y;
// using if/else
if (isset($x)) {
    return $x;
} else {
    return $y;

Please note that the null coalescing operator only evaluates to the right-hand side operand if the left-hand side operand is null or not set. This means that all other falsy values return the left-hand side operand.

The coalescing can also be chained (i.e. it returns the first defined/non-null value it encounters), for example:

$x ?? $y ?? $z ?? 'empty'; // output: 'empty'

In case there's no defined value in the coalescing chain, a "Notice: Undefined variable: ..." message is shown.

Starting with PHP 7.4, you can also use the null coalescing assignment operator ((??=)).

This post was published (and was last revised ) by Daniyal Hamid. Daniyal currently works as the Head of Engineering in Germany and has 20+ years of experience in software engineering, design and marketing. Please show your love and support by sharing this post.