Question

I have a string, in PHP and the string has occurrences of the pattern %%abc%%(some substring)%%xyz%%

There are multiple occurrences of such substrings within the master string.
Each of these occurrences need to be replaced with a string from within an array
array('substring1','substring2','substring3','substring4') depending upon the response of a function() which returns back a integer between 1 to 4.

I am not able to figure out an efficient way to do this.

Answer 1

This is a situation that calls for preg_replace_callback:

// Assume this already exists
function mapSubstringToInteger($str) {
    return (strlen($str) % 4) + 1;
}

// So you can now write this:
$pattern = '/%%abc%%(.*?)%%xyz%%/';
$replacements = array('r1', 'r2', 'r3', 'r4');
$callback = function($matches) use ($replacements) {
    return $replacements[mapSubstringToInteger($matches[1])];
};

preg_replace_callback($pattern, $callback, $input);