I am used to Java and therefore always think conditions are interpreted from left to right, i.e. there is a vital difference in null != $obj and $obj != null
Now this seems not to be the case with PHP.
Can I do something wrong in PHP when I always start with null on the left-hand side? Can I keep my behaviour from Java or do I need to train myself to do something else when dealing with PHP conditions?
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- There is no (technical) difference – nor is there in Java to my knowledge.
- In PHP, do not use either of these.
I recommend you always use the strict comparison operators === and !== if possible. You will know when you actually need loose comparison operators.
Misunderstandings
I believe you may be confused about a couple of things:
- short-circuiting operators
- order of evaluation
- operator precedence
I just found that the PHP manual says:
“PHP checks each condition in order from left to right”
No,
- the PHP manual does not say that, it’s a comment.
- PHP does not do that.
PHP evaluates the conditions from left to right, but it stops once the result is known:
expr1 && expr2
If expr1 evaluates to false, expr2 will not be evaluated. This is called short-circuiting and it does not seem to be very well-documented – I couldn’t find any other official note on the matter except for the comment in Example #1. It is a well-known feature, though.
Fallacies
I am used to Java and therefore always think conditions are interpreted from left to right, i.e. there is a vital difference in null != $obj and $obj != null
PHP checks each condition in order from left to right
Ergo: The same “best practice” can be applied
Ergo: nothing – non sequitur. The conclusion does not follow from the premise. Using constant == $variable or $variable == constant is not connected to either of short-circuiting, order of evaluation or operator precedence.
Undefined behavior
Both operands of != are always evaluated. In the case of PHP, the evaluation order (which is irrelevant here) is actually unspecified (as in absent from the documentation).
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Regarding your particular case another approach would be to used the built-in php function is_null. So you would end up with is_null($mixedValue) which would do all the work for you and properly do type comparison and everything else.
@phant0m: OK point taken… NEVER USE != or == always use !=== and === when you code with PHP. Therefore this question was wrong in the beginning, and there is no best practice with NULL on either side of the condition when it comes to PHP.
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