Consider a class which implements a lot of interfaces, would it make sense to implement each interface in a separate file using partial class definitions?
Would this be an abuse of the language feature or is it an idiom I'm unaware of?
If your class has to implement many interfaces, that's a reasonable way of managing the source, yes. You can edit the project file to make several of them depend on one "main" class file, which makes the Solution Explorer easier to work with.
You should ask yourself whether you shouldn't have several smaller classes each implementing a single interface though. Sometimes that will be a better approach, sometimes not - but it's always worth asking the question.
Not an idiom I have ever heard of, but sounds like an elegant way to partition your code.
I think that you should ask yourself if having a .cs file for each interface implemented by your class would make it easier or harder to understand the code. How would you name the files?
Although I might be going out on a limb here I think I'm going to suggest that you use the much hated #region directive instead if organizing the code is your goal.
You can, yes, but that won't give you any more advantages over, say, a single file with regions. Partial classes tend to be icky because it's not immediately obvious that there is another part to it, and someone else looking at the class might miss it. I personally prefer to have everything in one place.
The only benefit is to have the various interface implementations in separate physical files.
In my opinion, this is outweighed by the downside of having your class declaration located in separate physical files.
Pro: can easily pinpoint what part of a class that implement which interface (good when you are using tool that doesn't allow navigating easily through code inside the IDE).
Con: easier to lose context since now you have to navigate across multiple files
I supposed w/ the advance in IDE nowadays, it doesn't really matter. You can have a single file and let the tool help you navigate inside your class structure quickly. But then again tool can help either way... so...
Partial is still good for separating generated code vs custom code.
It makes about as much sense as having constructors in one partial class file, properties in another partial class file, etc., etc.
i.e. Don't do it unless you have a good reason.
I think there are better ways of structuring your code than using partials in this case. There's no reference in Visual Studio that you can consult to see how many partial implementations there are for a particular class so it is easy to lose track.
Depending on how much interfaces you really mean with "a lot of interfaces" you can use regions to separate the implementations. That would be fine up until 10-15 interfaces with a total of, say, 150 functions to implement. After that, things will get messy and you will lose overview. And that's where you will benefit from other mechanisms such as inheritance, encapsulation or aggregation, and the use of services and helper classes.
But I would seriously reconsider the architecture of your code if you ever come across the need to implement 15+ interfaces....
来源：https://stackoverflow.com/questions/4681179/implementing-interfaces-in-partial-classes