Difference between Category and Class Extension?

Question

What is the difference between a Category and a Class Extension. I believe both are used to add custom methods in existing classes. Can someone throw light on this? Examplif

Answer 1

Categories

Categories are used when you are creating file containing large number of methods.So they provide you with the facility to break a single class into different modules.Also if any changes are made to the categories the compiler does not waste time to compile the entire project.Categories are not able to add new variable or properties and look upto their parent class .You can override a method in a category but it isnt a good idea because the method cannot further be overridden.Also the flow can be effected because all categories have the same hierarchial level and hence two categories belonging to same parent class may exist at run time.Also protected methods can be created using categories

Extensions

Extensions enable you to override the property or add new property to the existing parent class.Syntatically same to categories they do not have name and are represented as @interface class() No .m file is present and method declared in extension have to be implemented in @implementation of parent file

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