Question

“abc”.respond_to?(:sub) returns true, but String.respond_to?(:sub) returns false.
The second returns false, because it asks whether objects of the class Class have a method sub, as String is an Object of Class. It is the same for methods()…

How do I do these things and especialy respond_to?() without creating an Object of that class.

Answer 1

If you are trying to confirm whether a method exists, String.method_defined? :sub will work. If you are specifically interested in instance methods, use something like:

String.instance_methods.index 'sub'

Note that you have to use a string, not a symbol.