Use verbs with functions, nouns with classes - what about interfaces?

Question

Ok, I understand the normal conventions of using verbs with functions and nouns with classes. What about interfaces? Is there any methodology when coming up with interface names that may not be that obvious?

Just to make it clear, I'm not talking about whether to put an "I" in front of the name or if to use camelCase or PascalCase. I'm wondering about the method of figuring out a clear, semantic name for an interface.

EDIT I'm obsessing on how to name an interface in the clearest way. I guess it just needs to be a noun too because when I think of naming classes I think of the closest "real" world object it can relate to. I suppose real world interfaces are things like a keyboard, mouse, remote control, ATM screen. Those are all nouns. Anyhow, any additional insight on a good way to formulate interface names would be appreciated.

Answer 1

I'd say it depends on what the interface defines. In some cases when the interface is rather specific and detailed, I think a noun is best. Examples are IList, ICollection.

Sometimes though an interface is more about adding certain general features to a class. In that case I think an adjective is best. Examples are IDisposable, IEnumerable, ...

Maybe another way to think about this is how many "abilities" your interface defines.

For example, the IList<T> interface defines these abilities: Add, Clear, Contains, Insert, Remove, ... These are all properties of a list so IList is a good name.

IDisposable on the other hand only defines one ability: Dispose. So it is suited for anything that is disposable. Hence the name IDisposable.

Answer 2

Since an interface is really just an expression of the "what" but not "how" of a type, I would name them in the same way that you name classes, at least from a parts of speech perspective. The only thing I might add to this is that they're often going to be more general than the specific implementers (e.g. "Customer" interface may have "ProspectiveCustomer" and "PayingCustomer" implementers).

Answer 3

Quick Answer: Interface is more about addition of a SET of abilities, features, common boundaries or interconnections between entities, classes, models, concepts, etc..

Thing about adding common behavior to classes and entities, and then a good meaningful name will come up to identify the set of realted features.

Interface Naming like : IStateMachineBuilder, IUserContextProviderBuilder, IEntityBuilderBuilder, IActiveAware, etc. probably explain the concept.

Answer 4

An interface describes behavior so the names should say so. I am not sure about a rule for this but you will know the name when you here it.

So examples,

Flyable      - Can Fly
Workable     - Can work
Negotiatable - Can negotiate.

I think it is not proper to name interfaces with I and call Set with ISet because as a developer you should not be worried whether it is an interface or a class. I see this practice does not exist in Java now.

Answer 5

An interface is used like a class. Therefore, it should also be named with a noun when you name classes with nouns. Prefer abstract nouns, for example "Vehicle" when the classes are "Car" and "Truck".