DuckSauce

Ruby is a duck typed language.

Yeah, I know. We've all heard that before. But what does that really mean? In theory, it means that if an object walks like a String, and talks like a String, then we should just treat it as a String. In other words, if you expect some variable to be a String, instead of checking if it is, just assume it is one and call String methods on it.

While this is a nice ideal to hold to, real world programs are rarely so simple. What's more, what if you want a method to be able to both accept not only String objects (or a duck-type String), but also objects that can be converted into a String (e.g. a Symbol)?

For this, there is the String() method in Ruby's Kernel module. Pass an object in, and you'll get a String-ish thing out, guaranteed. Ok, but what about your own classes? How should you handle the possibility that someone might not hand you an instance of your class, but instead an object that could still be converted into the right thing? That's the first place DuckSauce can help out, by letting you create converter methods for your own classes:

module MyApp
  include Ducktype

  class MyDataType
    #...
  end

  class OtherThing
    def to_my_data(other)
      # code to convert other to a MyDataType instance
    end
  end

  converter MyDataType, :to_my_data
end

This will create a method MyApp::MyDataType() that can be used to turn an instance of OtherThing (or any class that implements the to_my_data method) into an instance of your custom class. Don't worry, if the object already is an instance of MyDataType then this method is essentially a no-op.

Great, so now we can create our own methods like String() and Array(), but what about using them to convert our arguments? Don't worry, DuckSauce has you covered there as well:

module MyApp
  class MyDataType
    include Ducktype

    ducktype(first: MyDataType, second: String, third: Integer)
    def a_data_method(first, second, third)
      #...
    end
  end
end

The ducktype method decorator will ensure that each of the arguments first, second, and third are compatible with the MyDataType, String, and Integer classes, respectively, by using the Kernel level methods to make the check and/or conversion.

As this project is still extremely young, the biggest thing you can do to help right now is use it! If you find bugs, wish it worked a bit differently, or have some ideas on how it could be made even better, please use the issue tracker to let me know. If you are using it and would like to share any tips or tricks, please feel free to add a page to the wiki. Thanks!

Ducksauce Copyright (c) 2014, Joshua Ballanco.

Licensed under the BSD 2-Clause License. See COPYING for full license details.