Proper way to declare multiple vars in PHP

<?php
  $foo = $bar = $ping = $pong = '';
?>

If it's your script and you know which variables where you use, why you want spend recourses to check if the variable was declared before?

I posted this in a comment earlier, but someone suggested I submit it as an answer.

The shortest and simplest way I can think of, is to do:

$foo = $bar = $ping = $pong = '';

I often prefer to set things to false, instead of an empty string, so that you can always do checks in the future with === false, but that is just a preference and depends on how you are using these variables and for what.

Your if() with isset() attempt is the proper way of doing that!

But you can write it a little bit shorter/more readable, using the Ternary Operator:

$foo = isset($foo) ? $foo : '';

The first $foo will be set to the value after the ? when the condition after the = is true, else it will be set to the value after the :. The condition (between = and ? ) will always be casted as boolean.

Since PHP 5.3 you can write it even shorter:

$foo = isset($foo) ?: '';

This will set $foo to TRUE or FALSE (depending on what isset() returns), as pointed by @Decent Dabbler in the comments. Removing isset() will set it to '' but it will also throw an undefined variable notice (not in production though).

Since PHP 7 you can use a null coalesce operator:

$foo = $foo ?? '';

This won't throw any error, but it will evaluate as TRUE if $foo exists and is empty, as opposed to the shorthand ternary operator, that will evaluate as FALSE if the variable is empty.