PHP Lazy Boolean Evaluation

Question

I have a conditional statement thus:

if($boolean && expensiveOperation()){ ...}

Does PHP have lazy boolean evaluation, i.e. will it check $boolean and if it is false not bother performing the expensive operation? If so, what order should I put my variables?

I would generally refrain from putting 2 operations in the same line of code if they are not inherently related. It makes readability difficult and you don't gain computing time or resources. — Yishai Landau, Nov 18 '10 at 16:02
Apols for my incorrect answer (now deleted). I thought I remembered trying this out and finding it didn't work, but I'm obviously mistaken. — Nathan MacInnes, Nov 18 '10 at 16:05
@Nathan It shows you're responsible... or afraid of loosing reputation points. — Alin Purcaru, Nov 18 '10 at 16:10

score 32 · Accepted Answer · edited May 08 '14 at 15:26

32

Yes it does. It's called short-circuit evaluation. See the comments on the documentation page...

As for the order, it performs the checks based on Operator Precedence and then left to right. So:

A || B || C

Will evaluate A first, and then B only if A is false, and C only if both A and B are false...

But

A AND B || C

Will always evaluate B || C, since || has a higher precedence than AND (not true for &&).

edited May 08 '14 at 15:26

nullability

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answered Nov 18 '10 at 15:57

ircmaxell

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if you *want* the non-shor-circuit evaluation you can use a single & which would be a boolean union function. It would compute both values and then try to perform an AND between them. – Mikhail Nov 18 '10 at 15:59
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@Mikhail: Yes. But you must be careful as the singe `&` is actually a bit-wise operator. So `true & 2` would be false (since `true` is `00000001`, and `2` is `00000010`, so the `AND` would be `00000000`)... – ircmaxell Nov 18 '10 at 16:01
@Alin: Thanks! Dam google took me to the wrong docs... Fixed in the answer. Thanks! – ircmaxell Nov 18 '10 at 16:04

score 9 · Answer 2 · answered Nov 18 '10 at 15:58

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Yes, PHP does short-circuit evaluation.

answered Nov 18 '10 at 15:58

Gumbo

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score 3 · Answer 3 · answered Nov 18 '10 at 15:58

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PHP does have short circuit evaluation. Your example would be the proper use of it:

http://en.wikipedia.org/wiki/Short-circuit_evaluation#Support_in_common_programming_languages

answered Nov 18 '10 at 15:58

Jere

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PHP Lazy Boolean Evaluation

3 Answers3

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