Interface naming convention [closed]

Question

This is a subjective thing of course, but I don't see anything positive in prefixing interface names with an 'I'. To me, Thing is practically always more readable than IThing.

My question is, why does this convention exist then? Sure, it makes it easier to tell interfaces from other types. But wouldn't that argument extend to retaining the Hungarian notation, which is now widely censured?

What's your argument for that awkward 'I'? Or, more importantly, what could be Microsoft's?

Answer 1

Do prefix interface names with the letter I to indicate that the type is an interface.

The guideline doesn't explain why you should use the I prefix, but the fact that this is now an established convention should be reason enough.

What do you have to gain by dropping the I prefix?

Answer 2

It looks Hungarianish to me. Hungarian is generally considered a menace in strongly-typed languages.

Since C# is a Microsoft product and Hungarian notation was a Microsoft invention, I can see where C# might be susceptible to its influence.

Answer 3

In my opinion this 'I' is just visual noise. IDE should show class and interface names differently. Fortunately Java standard library doesn't use this convention.

Answer 4

I don't really like this convention. I understand that it helps out with the case when you have an interface and an implementation that would have the same name, but I just find it ugly. I'd still follow it if it were the convention where I am working, of course. Consistency is the point of conventions, and consistency is a very good thing.

I like to have an interface describe what the interface does in as generic a way as possible, for example, Validator. A specific implementation that validates a particular thing would be a ThingValidator, and an implementation with some abstract functionality shared by Validators would be an AbstractValidator. I would do this even if Thing is the only... well... thing that I'm validating, and Validator would be generic.

In cases where only one concrete class makes sense for an interface, I still try to describe something specific about that particular implementation rather than naming the interface differently to prevent a names collision. After all, I'm going to be typing the name of the interface more often than the name of the implementation.

Answer 5

Conventions (and criticism against them) all have a reason behind them, so let's run down some reasons behind conventions

• Interfaces are prefixed as I to differentiate interface types from implementations - e.g., as mentioned above there needs to be an easy way to distinguish between Thing and its interface IThing so the convention serves to this end.

• Interfaces are prefixed I to differentiate it from abstract classes - There is ambiguity when you see the following code:

  public class Apple: Fruit

  Without the convention one wouldn't know if Apple was inheriting from another class named Fruit, or if it were an implementation of an interface named Fruit, whereas IFruit will make this obvious:

  public class Apple: IFruit

  Principle of least surprise applies.

• Not all uses of hungarian notation are censured - Early uses of Hungarian notation signified a prefix which indicated the type of the object and then followed by the variable name or sometimes an underscore before the variable name. This was, for certain programming environments (think Visual Basic 4 - 6) useful but as true object-oriented programming grew in popularity it became impractical and redundant to specify the type. This became especially issue when it came to intellisense.

  Today hungarian notation is acceptable to distinguish UI elements from actual data and similarly associated UI elements, e.g., txtObject for a textbox, lblObject for the label that is associated with that textbox, while the data for the textbox is simply Object.

  I also have to point out that the original use of Hungarian notation wasn't for specifying data types (called System Hungarian Notation) but rather, specifying the semantic use of a variable name (called Apps Hungarian Notation). Read more on it on the wikipedia entry on Hungarian Notation.

Answer 6

I don't know exactly why they chose that convention, perhaps partly thinking of ensouling the class with "I" as in "I am Enumerable".

A naming convention that would be more in the line of the rest of the framework would be to incorporate the type in the name, as for example the xxxAttribute and xxxException classes, making it xxxInterface. That's a bit lengthy though, and after all the interfaces is something separate, not just another bunch of classes.