What if call_user_func is supposed to return false?

Question

The function I'm calling with call_user_func is supposed to return FALSE. So how do I detect errors if the callable is invalid?

(Side note: Why didn't they have this throw an exception rather than return an error code? Or is there a way to "catch" errors? I have an error handle. Should I have it throw exceptions for me?)

Answer 1

If you want to check if the function or method to be called really exists, you can use is_callable before calling call_user_func. You may wrap the whole thing in a function for easy reuse:

function call_uf($fn) {
    if(is_callable($fn)) {
        return call_user_func($fn);
    } else {
        throw new Exception("$fn is not callable");
    }
}

You asked in a comment about why PHP raises errors instead of using exceptions. I think that's because exceptions were introduced only in PHP5, so most PHP functions rely on error reporting. There seems to be a way around that, as the manual indicates:

Internal PHP functions mainly use Error reporting, only modern Object oriented extensions use exceptions. However, errors can be simply translated to exceptions with ErrorException.

Answer 2

They did not throw Exception because they need keep this function backward compatible. There was no Exception in older PHP versions, PHP < 5.

The boolean return type was "reserved" for function failure report. What you need to do is discover why the function would fail. I guess the only reason it would fail is for invalid arguments.

Maybe wraping it in a safe call would do what you want:

function safe_call_user_func()
{
  $nargs = func_num_args();
  $args = func_get_args();
  if ( $nargs == 0 )
    throw new RuntimeException( 'Require at least the callback param' );
  if ( !is_callable( $args[0] )
    throw new InvalidArgumentException( 'Callback param is invalid' );
  return call_user_func_array( array_shift( $args ), $args );
}