试图调用未知功能

I have to dynamically try, if function is callable (not only if exists, but if is callable). This is my code:

try {
  call_user_func($function, $arguments->arg);
} catch (Exception $e) {
  $condition = $this->_object->getContent("phpCall", "return");
}

$function and $arguments->arg are dynamic variables, for example $function contains md5 and $arguments->arg contains 123.

I know that function md5 exists in PHP, but I get this error: Warning: call_user_func() expects parameter 1 to be a valid callback, no array or string given in...

Any ideas?

Use is_callable

if (is_callable($function)){
    //do stuff here
}

If you're going to pass it to call_user_func, make sure $function is a string. Alternatively, you could just do:

    $function($args);

Sounds like call_user_func expects a string with the name of the function to be called. Are you instead sending a function pointer?