Why would you use 'custom attributes' in your code (.NET)

Question

Could anyone explain the benefits (or reasons) to use custom attributes in your code. Of course I use (and understand the purpose of) defined attributes in certain scenarios (WCF, Serialization etc.), but I cannot imagine any algorithms where I would need to create and use my own custom attributes. Could someone provide a real-world case where usages of custom defined attributes bring something to a project.

Answer 1

The same reason as for WCF etc, but something that's specific to your project - you want to add some metadata to some members (types, fields, methods, whatever) to specify something about the mechanism involved, and it's not something which is covered by existing attributes.

For example, NUnit wanted to add their own indication that a particular type contained unit tests - there was no such existing attribute, so they created TestFixtureAttribute.

It's a relatively rare event, sure - but it can happen.

Answer 2

If you want to write your own system like WCF, Serialization, etc...

If you write code that iterates over types or members and does things with them, you will frequently want to use your own custom attributes to mark some members as being different or special.