Aman kingrubyoo pnew

Ruby OOP: Objects over Classes Aman King king@thoughtworks.com RubyConf India 2010

What is OOP?

What is a class?

What is an object?

But before the serious stuff …

Detouring through a comic book universe … Image copyrighted by respective owners Source: http://www.comics.org/

Coming back …

What is an object?

Something that takes birth …

exhibits some behavior …

interacts with other objects …

and finally dies off or is simply forgotten …

all in an effort to solve a problem.

What is a class?

A container for related behavior …

that a new object can start off with.

A class itself is an object …

used to create other objects.

When creating a new object, a class calls the object’s private initialize method.

Typically a class is named …

referenced via a global constant variable.

A class object can have singleton methods added to it.

These singleton methods can be invoked wherever the class object is accessible …

aka “class-level methods”.

Why use classes?

Some possible reasons

An object remembers the class used to create it …

explicit type checking using kind_of? …

implicit type checking using case syntax …

implicit type checking using rescue syntax.

A class can build on other classes: inheritance.

A class can share state across multiple objects: @@class_variables.

Some good reasons

A named container of behavior can have more behavior added to it.

Any added behavior becomes part of all objects created by that class.

A class can represent a common pattern of initialization.

Classes improve readability and maintainability.

What a class is not?

The fundamental building block of an application.

A strong data type.

An enforcement of contract or limitations on how objects can behave.

Ruby’s object focus

Classes are objects.

No static method-lookup tables: chain of ancestors.

Singleton methods.

Private access modifier is object-level.

Duck typing.

Finding hints in the real world …

Objects over classes: Consequences

Classes and hierarchies no longer limit you.

Think through the usage of class-level methods and variables: globals?

Understanding meta-programming is easier.

Effective and confident use of meta-programming.

Final words

Objects are first-class citizens.

Classes are useful but secondary.

Thank you king@thoughtworks.com http://www.wikyblog.com/AmanKing

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