Protocol vs Interface [duplicate]

Question

I've been reading the swift documentation, and working through the playground. I have to admit I have zero knowledge of Objective-C/iOS development (outside of Xamarin at least). To my eyes, a protocol seemed identical to the C# interface.

However, I noticed whilst looking around on the web that Objective-C has a concept of both a protocol (source) and an interface (although I'm not really sure what the difference is). Swift doesn't seem to have both - just protocols.

Could someone explain, for swift, what the difference/relationship between a Protocol and a C# interface is?

Update: I appreciate that the answer might be functionally the same as the duplicates listed, but I think that, given that this is asking about a different language, that the question still has merit in it's own right. After all, new developers to swift might have no knowledge of Java (beyond Javascript, I have none). Placing an expectation on someone to have knowledge of a totally different language system in order to have the answer to their question is a bit much, isn't it!? This discussion on meta is also discussing this issue.

Answer 1

Objective C protocols serve basically the same purpose as interfaces in Java/ C#. Objective C interface files are different. Like C, Objective C has interface files that publicly declare the methods and properties of a class, that are then implemented in an implementation file. For example you may have an interface file of a class that looks something like this:

@interface  
-(void)myMethod;
@end

then in your implementation file you actually implement the method:

-(void)myMethod{
    //code
}

Swift does away with separate interface and implementation files. So it only has protocols.