test.rb

#!/usr/bin/env ruby

require 'spinny/utilities'

=begin
def foo
  def foo
    1
  end

  p foo

  2
end

p foo
=end

=begin
def add(num, num)
  num + num
end
safe :add,
  takes: [Integer, Integer],
  returns: Integer
=end

class Symbol
  def accepts(*accepted)
    _method = Spinny::Utilities.caller_method(self)

    calling_object.instance_exec(self, _method, accepted) do |method_name, _method, accepted|
      send(:define_method, method_name) do |*args|
        args.each_with_index do |arg, idx|
          expected = accepted[idx]
          actual   = arg.class

          next if arg.is_a?(expected)

          raise "Expected `#{arg.inspect}' to be #{expected}, got #{actual}"
        end

        _method.call(*args)
      end
    end

    self
  end

  # TODO: Handle more complex return types.
  def returns(*args)
    _method = Spinny::Utilities.caller_method(self)

    p Spinny::Utilities.caller_binding.receiver
    p calling_object
    return self

    calling_object.instance_exec(self, _method, accepted) do |method_name, _method, accepted|
      send(:define_method, method_name) do |*args|
        expected = accepted

        ret = _method.call(*args)

        raise "Expected `#{arg.inspect}' to be #{expected}, got #{actual}"

        ret
      end
    end

    self
  end

  private
  def calling_object
    Spinny::Utilities.caller_binding(1).receiver
  end
end

def add(num1, num2)
  num1 + num2
end
  .accepts(Numeric, Numeric)
  .returns(Numeric)

p add(1, 2)
p add('a', 'b')