if statement value position

Question

What is the difference between the 2 statements:

if (false === $variable) {
  //do something
}

and

if ($variable === false) {
  //do something
}

I personally use the second style but often run into code in frameworks that i use which always seem to use the first style.

Is there a difference ( i suspect it is some legacy thing to do with types) or is this simply a coding habit (it must be rooted in something though??)

If not, what is the reasoning behind the first style given that the logic is actually backwards.

possible duplicate of [Why do some experienced programmers write expressions this way?](http://stackoverflow.com/questions/3309089/why-do-some-experienced-programmers-write-expressions-this-way) — mario, Mar 24 '12 at 10:47
possible duplicate of [php false place in condition](http://stackoverflow.com/questions/9438043/php-false-place-in-condition) — mario, Mar 24 '12 at 10:48

score 0 · Answer 1 · answered Mar 24 '12 at 10:34

If you put the value that can't have something assigned to it (a literal, a constant, a function call, etc) on the left hand side then, if you accidentally use an assignment operator (=) instead of a comparison operator, then you'll get an error rather then a hard-to-track-down bug.

i.e.

if (false = $variable) { // Error
if ($variable = false) { // Valid code that doesn't do what you want

score 0 · Answer 2 · answered Mar 24 '12 at 10:35

0

This dates to C programming. It's a way to make sure "compilers" will fail if you accidently used = (assignment) and not == or === (equals) because "false" is not an lvalue (can't be on the left side of an assignment)

answered Mar 24 '12 at 10:35

Chen Harel

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score 0 · Answer 3 · answered Mar 24 '12 at 10:35

0

It stems from this:

if (false = $variable)

syntax error

if ($variable = false)

accidental assignment

answered Mar 24 '12 at 10:35

Corbin

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deceze · Accepted Answer · 2012-03-24T13:12:32.033

0

if ($foo = false) (note: = instead of ==) is a typical typo that leads to hard to debug problems. For that reason, some people prefer false == $foo, since the runtime will throw an error when you try to assign something to false.

Other than that there's no difference.

edited Mar 24 '12 at 13:12

answered Mar 24 '12 at 10:35

deceze

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score 0 · Answer 5 · answered Mar 24 '12 at 10:36

It has been around for a while. It comes from accidentally writing (by forgetting one =):

if (c = 1) {
}

which does assignment and it's doesn't actually check whether c equals 1. It assigns 1 and then it evaluates to 1 (so the if statement becomes always true due to that mistake). By writing

if (1 == c) {
}

as a habit, you cannot make that mistake. If you would forget the = in this case, the compiler would warn you because assignment to the literal 1 is not possible.

score 0 · Answer 6 · answered Mar 24 '12 at 10:40

Practically, the two statements are equivalent.

So, why to write it this way or the other (?) :

Try to avoid a typical typo : if ($condition = false) instead of if ($condition == false). In that case, your 2nd version would cause a difficult-to-debug issue, while the first would throw an error
Want to force one of the two parts of the conditional statement be evaluated first (the rightmost)

if statement value position

6 Answers6