views:

240

answers:

9

Is there a way in C# to mark a method as being part of a class to satisfy an interface that the class implements? I find myself wondering sometimes when digging in a class's code why some methods are there but then, when I try to remove one since it isn't in use, I see it's necessary in order for the class to implement some interface. It'd be nice to have these methods marked as such. Something like the @Override annotation in Java, maybe.

Edit: I would prefer to not explicitly implement the interface because then accessing the interface methods on an instance of my class becomes more of a hassle (i.e., having to cast an instance of MyClass to be IMyInterface before calling MyInterfaceMethod).

Edit: I would also prefer not to use regions. I don't want a big block of code described loosely through some arbitrary name as being part of an interface implementation, but rather to denote specific methods, wherever they may be within the class, as being part of an interface. Even some XML comment template that's intended for saying which interface the method belongs to would be nice.

Edit: All the answers seem to suggest I explicitly implement interfaces, which I don't want to do, or that I use regions, which I also don't want to do. I think Will understood my request best. I was hoping for something like an annotation, so I could do something like the following:

[Interface(IMyInterface)]
public void MyImplicitlyImplementedInterfaceMethod() { }

Or, as dss539 mentioned in a comment to this answer:

public implement void MyImplicitlyImplementedInterfaceMethod() { }

Much like we have override today: public override bool Equals(object obj) { }.

+4  A: 

You have three options:

Explicitly implement the interface:

You can explicitly implement the interface using the syntax IInterface.MethodName, for example:

bool IInterface.MethodName(string other) 
{
    // code
}

Wrap interface members in a region

Tools will already wrap your code in a region if you choose to "Implement an interface" through the UI:

#region IInterface members

public bool MethodName(string other)
{
    // code
}

#endregion

Document through comments

C# allows you to add multiple kinds of comments through //, /*, or XML documentation comments. Use liberally!

Michael Greene
If I explicitly implement the interface, calling that method is a pain because I have to cast my `MyClass` instance to be `IInterface` in order to access the method.
Sarah Vessels
For code clarity alone, you could wrap it in a `#region IInterface methods` and `#endregion` -- ReSharper, etc.. do this for you. You could also add comments of course.
Michael Greene
@Sarah: That's right, and that's what you want. Code to an interface, not to an implementation!
John Feminella
We always wrap our interface methods in regions. Makes it much easier to identify what's what.
Chris Lively
@Sarah: you only NEED to cast to the interface if you explicitly implement the interface as demonstrated. just adding the method with the signature the interface requires is implementing the interface, and the method is visible just like all other public methods.
Darren Kopp
No, Sarah obviously does NOT want to type ((IPerson)Bob).Age = 42. I can't really blame her, either.
dss539
Seriously? I get a downvote on this? First to answer, and give all options that I know of, and update for all of the OP's edits. Huh. Someone point me to what I should be doing differently, please.
Michael Greene
dss539: That's in an edit. I have updated each time she further clarifies what she wants.
Michael Greene
@Michael Sorry my last comment was @John who said "that's what you want". I am one of the -1 votes. (Sorry, nothing personal!) I really dislike 1) unenforced metadata [#region/comments] 2) explicit implementation. I commend your presentation of the ideas, however. Your answer is well written.
dss539
@Michael: I gave you an upvote for listing my possibilities. The fact that I don't like any of the current choices is not your fault. :) I'm, for the first time ever, wishing C# had a feature that Java already has.
Sarah Vessels
Thanks for the responses, helps me understand the thought process. Good luck finding what you want.
Michael Greene
A: 

You can explicitly implement the interface, but then the method won't be available on an instance of the class unless you first cast the class to that interface.

public Foo : IDisposable
{
    void IDisposable.Dispose()
    {
    }
}
Joel Mueller
+5  A: 

Surround them with #region MyInterface Members as Visual Studio does for you.

It reduces readability if you use #region only for interface members. If on the other hand you use it for private variables, properties, methods, events and different interface members the code will become much more readable. You can also group members by functionality.

One more option is to use a tool that does it for you. For example you can use NArrange - .NET Code Organizer/Formatter/Beautifier

Giorgi
This a common practice, but I find that it makes the code less readable.
dss539
Also, the compiler does not check the correctness of text in the `#region` block. Yes, of course it doesn't guarantee the correctness of comments, either. That's why I avoid comments where possible, too.
dss539
@dss539, Did you have a look at the updated answer?
Giorgi
@Giorgi Yes. It's obvious that the majority of people agree with you. [you win ;)] I, however, feel that #regions always (yes, always) reduce the readability of code. Also, as I mentioned in comments on other answers, there is no guarantee that your `#region` or comment is _true_. And it can easily become false if someone changes the interface.
dss539
+1  A: 

VB.NET has support for something like this, but not C#.

Will
As does Java. :(
Sarah Vessels
Please give an example of what VB.NET has.
John Saunders
@john my understanding was the asker (at the time I answered) was wanting to sort-of "hide" some of the public features of his types that were there only because they were a requirement of an interface. VB.NET will filter the intellisense for a type, hiding less used members.
Will
A: 
#region ISomeInterface implementation
public void Foo(){}
public void Bar(){}
#endregion
P Daddy
+2  A: 

Maybe you have deeper design issues if your class is implementing methods that you feel should be deleted.

Anyways, Resharper can help you out here.

http://www.jetbrains.com/resharper/documentation/presentation/overview/code_generation/Generate_demo.htm

Drag the slider to 10/69 to see the special "Implements interface" icon.

Resharper tells you which interface requires the method.

Edit: Also, if you mouse over the method name, it pops up text explaining where the method comes from. I'm not sure if this is part of Visual Studio or Resharper since I've used Resharper so long. Can anyone without Resharper installed confirm this?

dss539
It just seems like this should be part of the _language_, not require some extra plugin for a particular IDE.
Sarah Vessels
@Sarah Are you suggesting an `implements` keyword similar to the `overrides` keyword?
dss539
@dss539: yes! That would be awesome! Either a keyword like that, or in the form of Java annotations the way C# does stuff like that now, using square brackets.
Sarah Vessels
@Sarah It seems like `implements` would be possible in C#. However, there is *probably* some reason that it's an awful idea. I just can't think of a reason that it's bad, yet. ;)
dss539
@dss539: re 'deeper design issues'. Sometimes I want the convenience of using object initializers, for example, with a class, but never use some of the other methods that the same interface requires.
Sarah Vessels
@Sarah I'm not a huge fan of object initializers. I prefer constructor based dependency injection, where possible. Of course, having pseudo-support for named parameter passing is nice I guess. Sorry, back OT: Can you just create your own interface/abstract class that has only the properties you need?
dss539
@dss539: I might be able to do that, I just need to add all the methods an object initializer requires. I was thinking in at least one case, though, because my class didn't implement some particular interface, I couldn't use an instance of that class in a way I wanted to (not with object initializers).
Sarah Vessels
@Sarah If you can take a subset of the interface's contract and still find use for it, that is a sign that the subset you use should be extracted into a base interface. If you don't control that interface... well I guess you're stuck with it. :(
dss539
+1 for ReSharper. Whether or not this *should* be part of the language, it's unlikely that Microsoft will implement it anytime soon. ReSharper gives us this capability *now*.
TrueWill
A: 

Another way if your anti region would be to use the documentation comments like so:

///<summary>
/// Used for implementation of InterfaceX
///</summary>
public void Foo() {}
Joshua Cauble
This is equivalent to `#region` because it is unenforcable metadata. (Unless you have a tool that does static analysis on your comments... then that might be good.)
dss539
+1  A: 

Maybe you want to roll out your own Custom Attribute? - http://msdn.microsoft.com/en-us/library/sw480ze8(VS.80).aspx

You can create your own custom attributes by defining an attribute class, a class that derives directly or indirectly from Attribute, which makes identifying attribute definitions in metadata fast and easy. Suppose you want to tag classes and structs with the name of the programmer who wrote the class or struct. You might define a custom Author attribute class:

The example from above description. You may want this to apply to methods, and to be something similar to @Override in Java.

[Author("H. Ackerman", version = 1.1)]
class SampleClass
{
    // H. Ackerman's code goes here...
}
m3rLinEz
@m3rLinEz Can you write some code that will enforce the truth of the metadata contained in attributes? i.e. if you create an `[Implements("IPerson.Age")]` attribute, can you automatically verify the truth of this? If so, this seems to be exactly what the OP would want. If not, then it's equivalent to #region/comments. :(
dss539
Very cool! I didn't even know you could do this. Now, I wonder if there could be some way, through reflection, of enforcing that `[Implements(IMyInterface)]` could only be applied to a method if 1) the class implements `IMyInterface` and 2) that method is part of that interface. Craziness.
Sarah Vessels
@dss539 I agree about your point. This seems to be just a fancy way of using #comment, but this might provide a better semantic than plain comment.
m3rLinEz
A: 

Can you make use of an addin for Visual Studio? This will save you from marking up your code in a way that cannot be validated, but does have the downside that you will not be able to get the information when viewing the code outside of Visual Studio.

ReSharper adds an icon in the margin to signify this. Hover over it and it tells you which interface the method is from. Click it and it takes you to the interface.

ReSharper

I'd say that CodeRush probably does something similar.

adrianbanks