Evaluate a string as a condition

Question

I try to evaluate a string as a condition. An example will be great:

<?php
$vars = array(
    'VAR1' => 2,
    'VAR2' => -8,
    'VAR3' => 9,
);

evaluate('VAR1 <= 0', $vars); // should return false
evaluate('VAR1 <= 0 || VAR2 < 0', $vars); // should return true
evaluate('VAR1 < 10 && (VAR2 + VAR3) >= 0', $vars); // should return true

Any idea to implement evaluate() function ?

You'd need to implement a parser in evaluate to break apart the string into an actual conditional if you don't want to use eval. — MasterOdin, Mar 14 '15 at 13:09
[I answered a question](http://stackoverflow.com/a/20894727/1238344) a while back that may be useful to you: [*How can I apply my variables to a dynamic set of conditions?*](http://stackoverflow.com/questions/20893537/php-how-can-i-apply-my-variables-to-a-dynamic-set-of-conditions/20894727#20894727) — Emissary, Mar 14 '15 at 13:12
@Sony That's stupid. `eval` is not "dirty and dangerous" if you're using it on your own data, not user-input. Nobody is going to write your hypothetical `evaluate` function for you; this question is off-topic as you haven't included any attempt at a solution, only a list of requirements. — user229044, Mar 14 '15 at 13:28
A [shunting yard](http://en.wikipedia.org/wiki/Shunting-yard_algorithm) parser is usually easiest to do for such basic expressions - if you really feel like reimplementing `eval` in order to satisfy a meme. — mario, Mar 14 '15 at 13:29

score 0 · Answer 1 · answered Mar 14 '15 at 13:42

What about something like that:

$evaluation = sprintf('%d < 4', $var['VAR1']);  

if(assert($evaluation)){    
    echo 'true';
} else{ 
    echo 'false';
}

Sorry I wrote it quickly, I am sure you will find a better structure, also maybe if you will use often this operation could be necessary an object oriented approach.

Evaluate a string as a condition

1 Answers1