Using preg_replace_callback and create_function

Question

I am trying to replace the words in a sentence using preg_replace_callback.

"%1% and %2% went up the %3%"

should become

"Jack and Jill went up the hill"

I have given my code below.

<?php
  $values = array("Jack", "Jill", "hill");
  $line = "%1% and %2% went up the %3%";
  $line = preg_replace_callback(
    '/%(.*?)%/',
    create_function(
        // single quotes are essential here,
        // or alternative escape all $ as \$
        '$matches',
        'return $values[$matches[1]-1];'
    ),
    $line
  );
  echo $line;
?>

What I am getting is

" and went up the "

If I give return $matches[1]-1; , I am getting

"0 and 1 went up the 2"

Is it a scope issue ? How to make this working ? Any help would be appreciated.

jstephenson · Accepted Answer · 2012-02-24 09:08:05Z

2

It is indeed a scoping issue - your anonymous function created by create_function does not have access to $values.

This should work (>= PHP 5.3.0)

<?php
  $values = array("Jack", "Jill", "hill");
  $line = "%1% and %2% went up the %3%";
  // Define our callback here and import $values into its scope ...
  $callback = 
    function ($matches) use ($values)
    {
      return $values[$matches[1]-1];
    };

  $line = preg_replace_callback(
    '/%(.*?)%/',
    $callback, // Use it here.
    $line
  );
  echo $line;
?>

By declaring the callback function with use ($values), $values will be imported into its scope and available when it's called. This is the concept of a 'closure' over $values if you'd like to Google it further :).

Hope this helps.

answered Feb 24, 2012 at 9:08

jstephenson

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