Dynamic Conditional String - php

Question

I have the code below taken partially inside a function:
$dynamic_comparison = '';
if(($from == '')&&($to == '')){
$dynamic_comparison = 1;
}else if(($from != '')&&($to != '')){
$dynamic_comparison = '($row >= $from) && ($row <= $to)';
}else if(($from != '')&&($to == '')){
$dynamic_comparison = '($row >= $from)';
}else if(($from == '')&&($to != '')){
$dynamic_comparison = '($row <= $to)';
}
$form, $to and $row are the parameters of the function.
I want to evaluate $dynamic_comparison into something like this:
if($dynamic_comparison){
//A bunch of code here...
}
I tried:
if(eval($dynamic_comparison)){
//A bunch of code here...
}
It throws an error. How to get this right?

Answer 1

eval() is bad idea imho.
You can use anonymous function, like this
$dynamic_comparison = function($row, $to, $from) { return false };
if(($from == '')&&($to == '')){
$dynamic_comparison = function($row, $to, $from) { return true;};
}else if(($from != '')&&($to != '')){
$dynamic_comparison = function($row, $to, $from) { return ($row >= $from) && ($row <= $to);};
}else if(($from != '')&&($to == '')){
$dynamic_comparison = function($row, $to, $from) { return ($row >= $from);};
}else if(($from == '')&&($to != '')){
$dynamic_comparison = function($row, $to, $from) { return ($row <= $to);};
}
And use it like
if($dynamic_comparison($row, $to, $from))...
If you want to use eval anyway:
$dynamic_comparison = 'return false;';
if(($from == '')&&($to == '')){
$dynamic_comparison = 'return true;';
}else if(($from != '')&&($to != '')){
$dynamic_comparison = 'return ($row >= $from) && ($row <= $to);';
}else if(($from != '')&&($to == '')){
$dynamic_comparison = 'return ($row >= $from);';
}else if(($from == '')&&($to != '')){
$dynamic_comparison = 'return ($row <= $to);';
}
if(eval($dynamic_comparison)){//$to,$from,$row must be available in this scope

Answer 2

i think you have to use double quotes insted of single quotes for your string like this :
<?php
$dynamic_comparison = '';
if(($from == '')&&($to == '')){
$dynamic_comparison = 1;
}else if(($from != '')&&($to != '')){
$dynamic_comparison = "($row >= $from) && ($row <= $to)";
}else if(($from != '')&&($to == '')){
$dynamic_comparison = "($row >= $from)";
}else if(($from == '')&&($to != '')){
$dynamic_comparison = "($row <= $to)";
}
if you don't have $row initialezed at this moment , escape $ character :
<?php
$dynamic_comparison = '';
if(($from == '')&&($to == '')){
$dynamic_comparison = 1;
}else if(($from != '')&&($to != '')){
$dynamic_comparison = "(\$row >= $from) && (\$row <= $to)";
}else if(($from != '')&&($to == '')){
$dynamic_comparison = "(\$row >= $from)";
}else if(($from == '')&&($to != '')){
$dynamic_comparison = "(\$row <= $to)";
}
see eval() documentation : http://php.net/manual/en/function.eval.php