?: operator (the 'Elvis operator') in PHP – Dev

The best answers to the question “?: operator (the 'Elvis operator') in PHP” in the category Dev.


I saw this today in some PHP code:

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

I’m not familiar with the ?: operator being used here. It looks like a ternary operator, but the expression to evaluate to if the predicate is true has been omitted. What does it mean?


See the docs:

Since PHP 5.3, it is possible to leave out the middle part of the ternary operator. Expression expr1 ?: expr3 returns expr1 if expr1 evaluates to TRUE, and expr3 otherwise.


It evaluates to the left operand if the left operand is truthy, and the right operand otherwise.

In pseudocode,

foo = bar ?: baz;

roughly resolves to

foo = bar ? bar : baz;


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

with the difference that bar will only be evaluated once.

You can also use this to do a “self-check” of foo as demonstrated in the code example you posted:

foo = foo ?: bar;

This will assign bar to foo if foo is null or falsey, else it will leave foo unchanged.

Some more examples:

    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'

By the way, it’s called the Elvis operator.

Elvis operator


Another important consideration: The Elvis Operator breaks the Zend Opcache tokenization process. I found this the hard way! While this may have been fixed in later versions, I can confirm this problem exists in PHP 5.5.38 (with in-built Zend Opcache v7.0.6-dev).

If you find that some of your files ‘refuse’ to be cached in Zend Opcache, this may be one of the reasons… Hope this helps!


Be careful with arrays. We must write a checking variable after ?, because:

  $params = ['param1' => 'value1',
             'param2' => 'value2',
             'param3' => 'value3',];

  $param1 = isset($params['param1'])?:null;
  $param2 = !empty($params['param2'])?:null;
  $param3 = $params['param3']?:null; // get E_NOTICE, if $params['param3'] eq false

  true // would like to expect `value1`
  true // would like to expect `value2`
  param3 // properly, but problem above


From RFC. In PHP 7 the operator Null Coalesce Operator will do it, for example:

$param1 = $params['param1'] ?? null;
// Equivalent to:  $param1 = isset($params['param1']) ? $params['param1'] : null;