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
– Yishai Landau, Commented Nov 18, 2010 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
– Nathan, Commented Nov 18, 2010 at 16:05
@Nathan It shows you're responsible... or afraid of loosing reputation points. — Alin P.
– Alin P., Commented Nov 18, 2010 at 16:10

nullability · Accepted Answer · 2014-05-08 15:26:29Z

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 8, 2014 at 15:26

nullability

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answered Nov 18, 2010 at 15:57

ircmaxell

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3 Comments

Mikhail Over a year ago

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.

ircmaxell Over a year ago

@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 Over a year ago

@Alin: Thanks! Dam google took me to the wrong docs... Fixed in the answer. Thanks!

Pang · Accepted Answer · 2024-01-09 00:52:42Z

9

Yes, PHP does short-circuit evaluation.

edited Jan 9, 2024 at 0:52

Pang

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answered Nov 18, 2010 at 15:58

Gumbo

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Comments

Pang · Accepted Answer · 2024-01-09 00:54:51Z

3

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

https://en.wikipedia.org/wiki/Short-circuit_evaluation#Support_in_common_programming_and_scripting_languages

edited Jan 9, 2024 at 0:54

Pang

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answered Nov 18, 2010 at 15:58

Jere

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