Big O notation for Ruby methods?

Question

How can I find the complexity of a Ruby method?

For example length? If I look at the source code, I see this:

               static VALUE
rb_ary_len         


        

Answer 1

It is just O(1) for the length method. The length of an array is stored in a variable and can be returned without further calculations.

How to find out? By reading the source code and analysing the implementation and algorithms.