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I know that to an extent substitutes the lack of multiple inheritance by allowing one to include multiple modules within a class.

Also, I'm not sure of all of the prerequisites of a pure OOP Language. From this article, they mention

a Ruby class can have only one method with a given name (if you define a method with the same name twice, the latter method definition prevails..

So does it mean that Ruby doesn't support overloading methods? If so, it still can qualify as a pure OOP language? What is the reason behind this as well?

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    Please link to the definition of "pure OOP" that requires the language to support multiple inheritance. Commented Jul 16, 2013 at 15:14
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    Overloading has little to nothing to do with OOP. Commented Jul 16, 2013 at 15:17
  • @DanielHilgarth I might not be knowing all the prerequisites of pure OOP(that's why I've even mentioned that in my question). I thought multiple inheritance was one of them. I'm just seeing that it doesn't seem to be so. Commented Jul 16, 2013 at 15:44

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There are several different families of object-oriented languages. If you're thinking of multiple inheritance and method overloading, you're probably coming from a C++ mindset where these things are taken for granted. These conventions came from earlier languages that C++ is heavily influenced by.

Ruby doesn't concern itself with the type of objects, but rather the methods they're capable of responding to. This is called duck typing and is what separates Smalltalk-inspired languages like Ruby from the more formal Simula or ALGOL influenced languages like C++.

Using modules it's possible to "mix in" methods from various sources and have a sort of multiple inheritance, but strictly speaking it's not possible for a class to have more than one immediate parent class. In practice this is generally not a big deal, as inheritance is not the only way of adding methods.

Method overloading is largely irrelevant in Ruby because of duck-typing. In C++ you might have various methods for handling string, int or float types, but in Ruby you'd have one that calls to_f on whatever comes in and manipulates it accordingly. In this sense, Ruby methods are a lot more like C++ templates.

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Your quite right on me coming from a C++ background. +1 for your definition on duck typing and its relevance to Ruby. I just wanted to mention one thing, something I'm looking for in the context of my above question, what are those things (at least one of them) that can make you confidently say , Yes Ruby is a purely object oriented programming language. Hope that's not too much to ask.
The definition of "Object-Oriented" is pretty loose, but revolves around the idea of objects having methods and properties. The inheritance component is somewhat secondary and can be emulated if required. Everything, even numbers in Ruby, are objects, so it's about as "pure" as you can get, but you can still use it in a procedural or functional style.
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If multiple inheritance were the only "symptom" of a OOP language, then neither would Java, C#, Python, and many more be OOP languages.

What makes a language object-oriented in the first place are naturally objects. Everything is an object in ruby. The whole language is built on the concept of objects and data. Different objects can "communicate" between each other, you can encapsulate data, etc.

Take a look at this resource: Definitions for ObjectOriented.

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+1 for the link, even if it is a Pandora's Box to this question.
So can I say that one of the reasons that qualifies ruby to be a pure Object Oriented Programming Language is the very fact that everything in ruby is an object, something that can relate to the real world?
@sk4l +1 for being the first one to reinstate that one of the reasons why Ruby is a pure OOP Language is because everything in Ruby is an object and yes, a special thanks for the link too, it opens up the world of possibilities as to how different people perceive the term Object Oriented.
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In the first place, the problem of multiple inheritance makes sense only for an object oriented language. The very question of asking about multiple inheritance with Ruby itself proves that Ruby is an object oriented language.

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I have no doubts on Ruby being an OO Language. I'm just trying to better understand what makes Ruby purely object oriented, given that it doesn't support multiple inheritance and method overloading. Thanks for your answer.

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