# Interfaces in Ruby? **URL:** \ **Category:** Ruby\ **Created:** [December 7, 2005, 3:52am UTC](https://www.ruby-forum.com/t/interfaces-in-ruby/49638 "2005-12-07T03:52:18Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\ **Post date:** [December 7, 2005, 3:52am UTC](https://www.ruby-forum.com/t/interfaces-in-ruby/49638/1 "2005-12-07T03:52:18Z")
I’m new to Ruby - actually new to dynamically typed languages in general. I’m from more of a C++ and C# (strongly-typed and statically-typed) background. One thing I’m trying to wrap my brain around is the lack of explicit interface definitions. In C# we use interfaces so that client code can program against an abstract interface, and then you can give that client any concrete implementation of that interface as needed. Interfaces provide a level of abstraction/indirection that increase reusability and testability. Now, in Ruby, I like the “walk like a duck” approach. Actually, it’s similar to C++ templates which are very powerful. But there are two things that I worry about as I forge ahead in my new Ruby lifestyle: 1. In C# I can write code that can query an object for the interfaces it implements to find out what I can do with it. (Rarely used but sometimes a lifesaver). In Ruby I guess I have to use .methods to find out what methods it implements? 2. In C# I can insure that a function is given an object that implements a certain interface. If I don’t, it’s a compile-time error and I know it before I ship it. In Ruby, I won’t know if I accidentally pass in the wrong object until runtime. I might not catch it before I ship the code. Can anyone provide some enlightenment? Thanks! Jeff ---
**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\ **Post date:** [December 7, 2005, 4:04am UTC](https://www.ruby-forum.com/t/interfaces-in-ruby/49638/2 "2005-12-07T04:04:39Z")
On 12/6/05, Jeff C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 1. In C# I can write code that can query an object for the interfaces it > implements to find out what I can do with it. (Rarely used but > sometimes a lifesaver). In Ruby I guess I have to use .methods to find > out what methods it implements? You can use Mixins (Modules) and the query the mixins. So if your object includes Comparable or Enumerable, you can be sure it has the methods of these mixins > 1. In C# I can insure that a function is given an object that implements > a certain interface. If I don’t, it’s a compile-time error and I know > it before I ship it. In Ruby, I won’t know if I accidentally pass in > the wrong object until runtime. I might not catch it before I ship the > code. using respond\_to? is usually the way you can do this. See the Java / Ruby example below [http://www.kdedevelopers.org/node/1527](http://www.kdedevelopers.org/node/1527) > Can anyone provide some enlightenment? Write proper unit tests so you catch it before it goes out the door 🙂 HTH, Greg ---
**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\ **Post date:** [December 7, 2005, 5:21am UTC](https://www.ruby-forum.com/t/interfaces-in-ruby/49638/3 "2005-12-07T05:21:38Z")
On Dec 6, 2005, at 9:03 PM, Gregory B. wrote: > On 12/6/05, Jeff C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > 1. In C# I can write code that can query an object for the > > interfaces it > > implements to find out what I can do with it. (Rarely used but > > sometimes a lifesaver). In Ruby I guess I have to use .methods to > > find > > out what methods it implements? We generally use respond\_to?() for this, but I must stress be REALLY, REALLY sure before you check. Ruby is VERY dynamic. The object may not have the method you ask for until you call it. This is totally normal and okay. I’ve actually seen people check, so they can throw an Exception if it’s not there. Ruby was going to do that anyway. 😉 > > Can anyone provide some enlightenment? > > Write proper unit tests so you catch it before it goes out the door 🙂 This is first class advice right here. This should catch type issues and much, much more. The better you get at it, the more you will structure your code for testing (using small methods, for example). That just reduces type issues even further. And you gain so much freedom and power. I promise, when it clicks, you’ll never go back. “Free your mind…” 😉 James Edward G. II ---
**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\ **Post date:** [December 7, 2005, 3:21pm UTC](https://www.ruby-forum.com/t/interfaces-in-ruby/49638/4 "2005-12-07T15:21:04Z")
Jeff C. wrote: > One thing I’m trying to wrap my brain around is the lack of explicit > interface definitions. In C# we use interfaces so that client code can > program against an abstract interface, and then you can give that client > any concrete implementation of that interface as needed. Interfaces > provide a level of abstraction/indirection that increase reusability and > testability. As others have already noted in Ruby we generally do the simplest thing that will work – which is just calling methods in most cases. Where that doesn’t work we can still check for the presence of an included Module or methods. Or actually rescue the NoMethodError ourselves and try something else. There’s a lot of ways. Anyway – the reason for why I’m really posting is that I have played around with using unit tests for doing interfaces / contracts in Ruby. This can provide you with argument checking and similar things, but it is a toy. You can find this at [http://ruby-contract.rubyforge.org/](http://ruby-contract.rubyforge.org/) It might also give you a general idea of how much power you can get out of Ruby’s dynamic nature.