When to use " is same as" and when to use "=="

Question

{% if foo is same as('bar') %}

vs.

{% if foo == 'bar' %}

When to use first and when to use second? Does one of them has advantages over another?

Answer 1

Looking at the Twig code, they have this documented for the “same as” test:

Checks if a variable is the same as another one (=== in PHP).

I won’t re-hash the details of === vs. == in PHP because there is an excellent comparison here: https://stackoverflow.com/questions/80646/how-do-the-php-equality-double-equals-and-identity-triple-equals-comp

The money quote is:

== compares the values of variables for equality, type casting as necessary. === checks if the two variables are of the same type AND have the same value.

And here’s what the PHP docs have to say:

http://www.php.net/manual/en/language.operators.comparison.php

Answer 2

For example:

false == 0 will be true

false === 0 will be false

It is very useful when you use such functions as file_put_contents() and preg_match().

The first function returns a number of bytes writtent to the file (which can be 0 if nothing was written what does not mean that it's false). And the second one returns 1 if something was found otherwise 0.

They always warn people when you must check for the variable type too. Php.net: Go at "Return values" and you will see a red Warning block.