C#•17mo ago

✅ Methods (with bodies) in interfaces

Hi!
C# allows interfaces to contain methods already with some implementation (i.e. with body).
As I can easily think about taking advantage of this, but doesn't it deny the main reason interfaces exists - i.e. to abstract things?
If it were your decision whould you use this functionality in your project or stick only to other options (like putting logic inside abstract classes, using services, etc.)?

Angius•8/12/24, 3:30 PM

It's a contentious addition to the language, for sure

Angius•8/12/24, 3:30 PM

The idea is it makes refactoring easier

Angius•8/12/24, 3:30 PM

And... that's about when it should be used

Angius•8/12/24, 3:31 PM

I'd certainly not use it as a substitute for multiple inheritance or anything like that

Angius•8/12/24, 3:32 PM

Basically, the scenario is that you need to add some member to the interface, but that would require you to implement that member in all 67535 classes that implement the interface. That can often be a lot, so you start by implementing it in the few classes that need it right now, while the default interface implementation lets other classes not implement the member for now

Angius•8/12/24, 3:33 PM

It should be used for placeholders, basically

Jimmacle•8/12/24, 3:34 PM

i see it as a tool to maintain backwards compatibility, if you have an interface that's implemented by other code, if you add methods to it you can provide a default implementation so that the consuming code doesn't immediately break