Partial Class vs Extension Method

Question

I dont have much experience of using these 2 ways to extend a class or create extension methods against a class. By looking others work, I have a question here.

I saw pe

Answer 1

Some of differences that will determine whether you want to use a Partial Class or an Extension Method are

Partial Class

• Only works against classes in the same project/assembly
• Target class has to be marked as partial
• Has access to the Target class' fields and protected members
• Target must be a class implementation

Extension Method

• Can be applied against classes in other assembles
• Must be static, has access to only the Target classes public members
• Target of extension can be a concrete type, or an abstract type or interface

Answer 2

Partial Class - 

split the definition of a class or a struct, or an interface over two or more source files

Extension Method  

Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type

Answer 3

I use partial methods when I need a class to implement an interface, but the class code is autogenerated (VS uses partial classes to generate code for both web services and EF models).

I use extension methods when the new method that I'm adding to the type is appropriate for any value of that type. (good examples: int.IsEven(), string.IsEmpty(); bad examples: int.IsOldEnoughToDrive(), string.IsLastName()).