CODEWITHSUNDEEP
phpfunctionlazy-evaluationboolean-logic
user86337
user86337

Reputation:

How can I have PHP avoid lazy evaluation?

I have an interesting question about the way PHP evaluates boolean expressions. When you have, for example,

$expression = $expression1 and $expression2;

or

if ($expression1 and $expression2)

PHP first checks if $expression1 evaluates to true. If this is not the case, then $expression2 is simply skipped to avoid unnecessary calculations. In a script I am writing, I have:

if ($validator->valid("title") and $validator->valid("text"))

I need to have the second statement ($validator->valid("text")) evaluated even if the first one evaluates to false. I would like to ask you whether there is some easy way to force PHP to always evaluate both statements. Thank you!

Upvotes: 2

Views: 4161

Answers (6)

Zorf
Zorf

Reputation: 6464

You can define a function like:

function logical_and($x,$y) {return ($x && $y);}

Since PHP uses call-by-value, this works.

Upvotes: 1

Matt
Matt

Reputation: 2230

Alternatively, if you can modify the class $validator instantiates, you could make the valid method accept a string or an array. If it's an array, it runs the code that already exists on each item and only returns TRUE if all items are "valid".

Upvotes: 0

Paolo Bergantino
Paolo Bergantino

Reputation: 488544

This is known as short circuit evaluation, and to avoid it you need to do this, using a single &:

if($validator->valid("title") & $validator->valid("text")) {

}

Note that this is not using logical operators but actually bitwise operators:

They're operators that act on the binary representations of numbers. They do not take logical values (i.e., "true" or "false") as arguments without first converting them to the numbers 1 and 0 respectively. Nor do they return logical values, but numbers. Sure, you can later treat those numbers as though they were logical values (in which case 0 is cast to "false" and anything else is cast to "true"), but that's a consequence of PHP's type casting rules, and nothing to do with the behavior of the operators.

As such, there is some debate as to whether it is good practice to use this side effect to circumvent short-circuit evaluation. I would personally at least put a comment that the & is intentional, but if you want to be as pure as possible you should evaluate whether they are valid first and then do the if.

Upvotes: 9

chosta
chosta

Reputation: 448

try to evaluate each term separately:

$term1 = $validator->valid("title");
$term2 = $validator->valid("text");
if($term1 && $term2) {
//things to do
}

Upvotes: 4

dmondark
dmondark

Reputation: 1687

This might not be the best implementation, but you could always do:

$a=$validator->valid("title");
$b=$validator->valid("text");
if($a && $b) {...}

Upvotes: 3

Kalium
Kalium

Reputation: 4682

$isValidTitle = $validator->valid("title");
$isValidText = $validator->valid("text");
if($isValidTitle && $isValidText)
{
    ...
}

Will that suit?

Upvotes: 28

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