php: Why preg_replace_callback does not allow built in php functions, just anonymous user functions?

Question

This does not work, and outputs an empty string:

$check["pattern"] = "correct";
$text = "Could this be correct?";
echo preg_replace_callback($check["pattern"],ucfirst,$text);

Would have been nice to use built in functions. In fact general callbacks do allow built in functions as per http://php.net/manual/en/language.types.callable.php, but not preg_replace_callback. Could be a feature request for php?

Answer 1

Your code should trigger a notice and a warning:

• Notice: Use of undefined constant ucfirst - assumed 'ucfirst'
• Warning: preg_replace_callback(): Delimiter must not be alphanumeric or backslash

If it doesn't, you seriously need to check your PHP error reporting settings. Fixing the code with the help of the error messages:

$check["pattern"] = "/correct/";
$text = "Could this be correct?";
echo preg_replace_callback($check["pattern"],'ucfirst',$text);

... we get this:

Warning: ucfirst() expects parameter 1 to be string, array given

So using a builtin callback function is working fine. However, as the manual page for ucfirst() explains, the function expects a string, not an array. And, as the manual page for preg_replace_callback() explains:

A callback that will be called and passed an array of matched elements in the subject string.

To sum up: it isn't a sensible feature request, it's a bug in your code ;-)