understanding-class_eval-instance_eval-and-define_method

MetaTest.rb

class Test
    class_eval <<-END
        def self.a
            puts "a"
        end
    END

    instance_eval <<-END
        def b
            puts "b"
        end
    END

    instance_eval do
        define_method(:c) do
            puts "c"
        end
    end

    class << self
        define_method(:d) do
            puts "d"
        end
    end
end