Coalesce function for PHP?

Question

Many programming languages has a coalesce function (example). PHP, sadly, does not.

What would be the most efficient way to implement one in PHP?

Answer 1

First hit for "php coalesce" on google.

function coalesce() {
  $args = func_get_args();
  foreach ($args as $arg) {
    if (!empty($arg)) {
      return $arg;
    }
  }
  return NULL;
}

http://drupial.com/content/php-coalesce

Answer 2

I'm currently using this, but I wonder if it couldn't be improved with some of the new features in PHP 5.

function coalesce() {
  $args = func_get_args();
  foreach ($args as $arg) {
    if (!empty($arg)) {
    return $arg;
    }
  }
  return $args[0];
}

Answer 3

Make sure you identify exactly how you want this function to work with certain types. PHP has a wide variety of type-checking or similar functions, so make sure you know how they work. This is an example comparison of is_null() and empty()

$testData = array(
  'FALSE'   => FALSE
  ,'0'      => 0
  ,'"0"'    => "0" 
  ,'NULL'   => NULL
  ,'array()'=> array()
  ,'new stdClass()' => new stdClass()
  ,'$undef' => $undef
);

foreach ( $testData as $key => $var )
{
  echo "$key " . (( empty( $var ) ) ? 'is' : 'is not') . " empty<br>";
  echo "$key " . (( is_null( $var ) ) ? 'is' : 'is not')  . " null<br>";
  echo '<hr>';
}

As you can see, empty() returns true for all of these, but is_null() only does so for 2 of them.

Answer 4

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

Answer 5

It is worth noting that due to PHP's treatment of uninitalised variables and array indices, any kind of coalesce function is of limited use. I would love to be able to do this:

$id = coalesce($_GET['id'], $_SESSION['id'], null);

But this will, in most cases, cause PHP to error with an E_NOTICE. The only safe way to test the existence of a variable before using it is to use it directly in empty() or isset(). The ternary operator suggested by Kevin is the best option if you know that all the options in your coalesce are known to be initialised.