Coalesce function for PHP?

Many programming languages have a coalesce function (returns the first non-NULL value, example). PHP, sadly in 2009, does not.

What would be a good way to implement one in PHP until PHP itself gets a coalesce function?

There is a new operator in php 5.3 which does this: ?:

// A
echo 'A' ?: 'B';

// B
echo '' ?: 'B';

// B
echo false ?: 'B';

// B
echo null ?: 'B';

Source: http://www.php.net/ChangeLog-5.php#5.3.0

PHP 7 introduced a real coalesce operator:

echo $_GET['doesNotExist'] ?? 'fallback'; // prints 'fallback'

If the value before the ?? does not exists or is null the value after the ?? is taken.

The improvement over the mentioned ?: operator is, that the ?? also handles undefined variables without throwing an E_NOTICE.

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