Rubysierung

# ruby >= 2.1.0
# You can only use Rubysierung in a file context, see issue #5 and #7.
gem 'rubysierung'

require 'rubysierung'

# define a custom types
class Strict::CustomType;end
class CustomType;end

class Strict::CustomTypeX;end
class CustomTypeX;end

class Example
  extend Rubysierung

  # if the type doesnt match Rubisierung will raise an Error messages

  # add custom Types
  # if you don't specify a Strict Type the standard type is being set for it
  # [TypeClass, StandardConversionMethodAsSymbol, StrictConversionMethodSymbol]
  @__add_type[CustomType, :to_s, :to_str]
  @__add_type[CustomTypeX, :to_s]

  # define foo to respond to :to_s and bar to :to_i
  def one(foo: String, bar: Integer)
    [foo, bar]
  end

  # you can still define empty/default parameters
  def self.two(foo:, bar: 'hello World')
    [foo, bar]
  end

  # use a custom type
  def self.three(foo:, bar: CustomType)
    [foo, bar]
  end

  # define foo to respond to :to_str (strict type)
  def self.four(foo: Strict::String, bar: Integer)
    [foo, bar]
  end

  # with default parameters
  def self.five(foo: String||'I am a default :)', bar: Integer||42)
    [foo, bar]
  end
end

def one(foo:, bar:)
  sFoo = foo.to_s
  iBar = bar.to_i
  [sFoo, iBar]
end