What is the Elvis Operator (?:) and How Does it Work in PHP?

Elvis Operator (?:) Unraveled in PHP

In the depths of a complex PHP codebase, you may encounter a mysterious operator: the ?: operator. Dubbed the "Elvis operator," it may have you wondering, "What's its purpose?"

The ?: operator, in essence, evaluates to its left operand if the left operand is considered "truthy," and the right operand otherwise. In other words:

foo ?: bar

is roughly equivalent to the ternary operator:

foo ? foo : bar

or in a traditional if-else statement:

if (foo) {
    foo = foo;
} else {
    foo = bar;
}

However, unlike the ternary operator, the ?: operator evaluates the left operand only once, enhancing efficiency.

Example Usage

One common use case is for self-checking, as seen in the code snippet:

$items = $items ?: $this->_handle->result('next', $this->_result, $this);

Here, it assigns the result of $this->_handle->result() to $items if $items is null or falsey, while leaving $items unchanged otherwise.

Additional Examples

Here are a few more examples to illuminate the behavior:

var_dump(5 ?: 0); // 5
var_dump(false ?: 0); // 0
var_dump(null ?: 'foo'); // 'foo'
var_dump(true ?: 123); // true
var_dump('rock' ?: 'roll'); // 'rock'
var_dump('' ?: 'roll'); // 'roll'
var_dump('0' ?: 'roll'); // 'roll'
var_dump('42' ?: 'roll'); // '42'

Should you encounter a ?: operator in the future, remember that its goal is to provide a concise way to evaluate and assign based on truthiness, making your code more efficient and readable.

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