imitate sorbet typecheker

signature.rb

#! env ruby
class CodeSignature
  def initialize(args)
    @args = args
  end

  def returns(klass)
    @ret = klass
    puts "CodeSignature: @args = #{@args.inspect}"
    puts "CodeSignature: @ret = #{@ret.inspect}"
    self
  end
end

class Module
  def sig(args)
    CodeSignature.new(args)
  end
end

class A
  sig(foo: Integer).returns(String)
  def bar(foo)
    foo.to_s
  end
end

if $0 == __FILE__
  a = A.new
  a.bar(1)
  a.bar("hoge")
end

RDLだと全部文字列で書くことになる

type '(Integer) -> String'