Objective C Runtime's class_respondsToSelector to detect if whether instances of a class respond to a particular selector.

ClassRespondsToSelector.m

/**
 * class_respondsToSelector
 * Returns a Boolean value that indicates whether instances of a class respond to a particular selector.
 * Overall, class_respondsToSelector looks up the selector in the class's method table to see if it has an entry
 *
 * BOOL class_respondsToSelector(Class cls, SEL sel)
 *
 * Parameters
 * cls
 * The class you want to inspect.
 *
 * sel
 * A selector.
 *
 * Return Value
 * YES if instances of the class respond to the selector, otherwise NO.
 *
 * Warning
 * You should usually use NSObject's respondsToSelector: or instancesRespondToSelector: methods instead of this function.
 *
 **/

- (BOOL)respondsToSelector: (SEL)aSelector
{
  return class_respondsToSelector(isa, aSelector);
}