PHP - reversed order in if statement

Question

This is a question that is bugging me for a long time and can't find any answer... Noticed it's used quite a lot by Zend Framework Developers,

What is the difference between following 2 "if" statements? :

if (null === $this->user) { ... }

if ($this->user === null) { ... }

To me the first one looks kinda odd ;]

Thanks for answer.

Answer 1

This is not a difference for the way your script works, it's just a coding standard, a recommendation

The reason why it is recommended to use it this way:

if (null == $this->user)

is the fact that if you mistype and write = instead of == you will get an error, while

($this->user = null)

instead of

($this->user == null)

works but causes weird bugs (assignment and the final value is evaluated as bool instead of comparison)

and I guess it just extended as a habit to the strict comparison operator (===)

Update: since I see that there's still some activity on this thread even 3 years after I posted the answer I figured I would add something I forgot to mention. This type of notation is known as yoda conditions, you can read more about it on this wikipedia page for example.

Answer 2

It is a good practice for writing if statement. Consider this code:

if (10 == $var) {
  echo 'true';
} else {
  echo 'false';
}

If you forgot one equal sign:

if (10 = $var) { }

Then PHP will generate parse error, so you know you missed one = and you can fix it. But this code:

if ($var = 10) { }

will assign 10 to $var and always evaluates to true condition. Whatever the contents of $var, the code above will always echo 'true' and its very difficult to find this bug.