Can I store a logical comparison in a string?

Question

I am trying to modularise a lengthy if..else function.

$condition = "$a < $b";
if($condition)
{
    $c++;
}

Is there any way of translating the literal string into a logical expression?

You *could* do this with `eval`, but the standard approach would be to define a bunch of functions... — Oliver Charlesworth, Jan 24 '13 at 01:24
maybe you should explain, what exactly you mean with "modularise". — Fabian Schmengler, Jan 24 '13 at 01:36
Please show your lengthy if..else block (not function). I'm almost sure, the solution isn't 'modularizing'. — markus, Jan 24 '13 at 01:37
Lenghty if else blocks are often a sign that you're violating some principles of clean coding. — markus, Jan 24 '13 at 01:39

Fabian Schmengler · Accepted Answer · 2013-01-24T01:33:23.410

7

I am trying to modularise a lengthy if..else function.

You don't need to put the condition in a string for that, just store the boolean true or false:

$condition = ($a < $b);
if($condition)
{
    $c++;
}

the values of $a and $b may change between definition of $condition and its usage

One solution would be a Closure (assuming that definition and usage are happening in the same scope):

$condition = function() use (&$a, &$b) {
    return $a < $b;
}
$a = 1;
$b = 2;
if ($condition()) {
    echo 'a is less than b';
}

But I don't know if this makes sense for you without remotely knowing what you are trying to accomplish.

edited Jan 24 '13 at 01:33

answered Jan 24 '13 at 01:25

Fabian Schmengler

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the values of $a and $b may change between definition of $condition and its usage. – hek2mgl Jan 24 '13 at 01:26
If you remove the part above the closure stuff it would be the best answer (what it already is :) ) – hek2mgl Jan 24 '13 at 01:40
I won't remove it to leave the answer more generalized for future readers. Pick what you need ;) – Fabian Schmengler Jan 24 '13 at 01:43
1

You will be happy to hear that you are wrong :) Otherwise my first solution would be perfectly fine. Did you notice the references (`&`) in the use clause? – Fabian Schmengler Jan 24 '13 at 01:51

score 2 · Answer 2 · edited Jan 24 '13 at 02:55

2

Use lambda if you know variables that are enough to determine result

$f = function ($a, $b) { return $a < $b; }

if ($f($x, $y)){}

edited Jan 24 '13 at 02:55

Ja͢ck

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answered Jan 24 '13 at 01:32

RiaD

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+1. Though you don't need lambda here, just a plain old function declaration will do just as well :) – Ja͢ck Jan 24 '13 at 03:11

score 1 · Answer 3 · answered Jan 24 '13 at 01:26

1

you could do this using eval. not sure why you wouldn't just evaluate the condition immediately, though.

answered Jan 24 '13 at 01:26

Mike Corcoran

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`eval` is never the solution of the problem. We should avoid using it. – Kasyx Jan 24 '13 at 12:06

Ricardo Ortega Magaña · Answer 4 · 2013-01-24T04:26:38.247

-3

<?php
     $a=0;
     $b=1;
    function resultofcondition()
    {
        global $a,$b;
        return $a<$b;
    }
    if(resultofcondition()){
        echo " You are dumb,";
    }else{
        echo " I am dumb,"; 
    }
    $a=1;
    $b=0;
    if(resultofcondition()){
        echo " You were correct.";
    }else{
        echo " in your face.";
    }
?>

Indeed thanks for commenting that out, was missing the GLOBAL parameter, for those who voted down, what would that code output? ¬_¬ w/e have fun xD

edited Jan 24 '13 at 04:26

answered Jan 24 '13 at 01:25

Ricardo Ortega Magaña

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This does not work in PHP, `$a` and `$b` are not available in the function scope. – Fabian Schmengler Jan 24 '13 at 01:34
@RicardoOrtegaMagaña They most certainly are not, unless you use `global $a, $b;` – Ja͢ck Jan 24 '13 at 02:55
This last comment doesn't add anything useful to the answer. – Gustavo Rodrigues Mar 27 '15 at 14:25

Can I store a logical comparison in a string?

4 Answers4