The Elvis operator and the Null coalescing operator are both binary operators that allow you to evaluate an expression/variable and define a default value when the expression/variable is not available.

The Elvis operator

The Elvis operator is used to return a default value when the given operand is false.
Its name comes from the resemblance of the notation ?: with the hairstyle of the famous singer.

Usage in PHP:

$variable = [];
$result = $variable ?: 'default value';
echo $result; // Outputs: default value (since an empty array is considered falsy)

Equivalent with a Ternary condition:

$variable = [];
$result = $result ? $result : 'default value';

The Null coalescing operator

Quite similar to the Elvis operator, the null coalescing operator returns a default value when the given operand is null or undefined.

Usage in PHP:

$variable = [];
$result = $variable ?? 'default value';
echo $result; // Outputs: [] (since an empty array is not null)

Equivalent with a Ternary condition:

$variable = [];
$result = isset($result) ? $result : 'default value';