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

Here is my understanding :

Extensions are usually used to add extra features to our own "custom class". We can add private methods or properties extending the class interface which can be used within the implementation of the class.

Extensions are to be written within the same file as the class. Hence you cannot write extensions for pre defined types like String, Float, etc.

On the other hand Categories can be used to add extra methods to a pre existing classes. Example we can create our own methods by extending String class. Note that we cannot create extra properties in the categories. Also main advantage of categories is we can write the categories in any other file, outside the file where your class exits.

Also while creating categories you are supposed to give a name for it within the brackets. But for extension no name is required. Hence some times they are also called anonymous categories.