ruby2-7.rb

class Foo
  class << self
    def method_missing(meth, *args)
      if new.respond_to? meth
        new.send(meth, *args)
      else
        super
      end
    end

    def respond_to_missing?(meth, _)
      new.respond_to?(meth) || super
    end
  end

  def foo(a: "default A", b: "default B")
    puts "a: #{a}, b: #{b}"
  end

  def call_foo(*args)
    foo(*args)
  end

  def elements(elements)
    elements.each{|el|
      puts el
    }
  end

  def elements2(elements, key:)
    elements.each{|el|
      puts el
    }

    puts key
  end
end

Foo.call_foo(a: "it's an a!", b: "it's a B")
Foo.call_foo({a: "it's an a!", b: "it's a B"})
Foo.call_foo
Foo.elements([1, 2])
Foo.elements2([1, 2], key: "A key")