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?
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;
or
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:
<?php
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.