[SOLVED] Help understanding === vs. ==

[nloding]

I'm a little confused.  I see this more and more often when I look at open-source apps:

 

if(''===$var)

 

In every article, every book, that I have ever read (not that I've read nearly everything or that everything I've read was good), it's always been this:

 

if($var=='')

 

What's the difference between '===' and '==', and why put the value first instead of the variable?  Is there a performance or accuracy difference?  Is '===' case-sensitive?  How can it be more strict than '=='?  I Googled it, but some of the things I read made me more confused ...

[DeanWhitehouse]

This will help

http://uk3.php.net/manual/en/language.operators.comparison.php

 

PHP Manual:

$a === $b  Identical  TRUE if $a is equal to $b, and they are of the same type. (introduced in PHP 4)

[nloding]

OK, so they are of the same type, that makes sense.

 

Is there anything to putting the value or the variable first during comparison?

[DeanWhitehouse]

No putting the var after, wouldnt be the same as putting it before.

 

e.g.

if($var != '')

 

is not the same as

 

if('' != $var)

 

 

As they will return different results , so i think.

[Mchl]

Blade280891: both evaluate same here

 

 

There shouldn't be anything to it, as far as I know. I think it's just personal preference.

 

[DeanWhitehouse]

If you look at it logically , you are saying

 

if variable one doesnt equal empty , then do

if($var != '')

 

or

 

if empty doesnt equal variable one , then do

if('' != $var)

[Mchl]

Which is exactly the same (at least in boolean logic - lawyers might have different opinion )

[nloding]

If you look at it logically , you are saying

 

if variable one doesnt equal empty , then do

if($var != '')

 

or

 

if empty doesnt equal variable one , then do

if('' != $var)

 

Yeah, but logically, to me, those end up with the same result.  Either they are equal or they aren't.  2 * 3 = 6, and 6 = 3 * 2.  I was just curious if there was performance difference or something, but it sounds like I'll have to bench it to find out.

[448191]

Of course that's the same.

 

The primary motivation for people placing the value in the comparison on the left side is that it makes in impossible to accidentally use assignment instead of comparison.

[Mchl]

!!

That makes sense!

[nloding]

makes in impossible to accidentally use assignment instead of comparison.

 

Never would have occurred to me.  That's a great idea though.