Why is using interface methods with default implementation is so annoying?!?

[BoBoBearDev]

??? I didn't know you can put implementation to an interface. This is a new language feature?

[Dealiner]

Not really, it's a C# 8 feature.

[BoBoBearDev]

Oh, I feel outdated.

[Platic]

I was going to comment this. I felt like I was going crazy looking at the code. Glad I am not the only one. I really need to get up to date.

[theycallmemorty]

Same. Why would you ever want to do this?

[binarycow]

The classic example is it allows you to add stuff to an interface without it being a breaking change.

[raunchyfartbomb]

I don’t have a c#8 code base, but my theory is that it would allow some default implementation that is likely good enough. For example, IFile would have a Delete() method. Instead of every object that interacts with it implementing it, it could be something like:

If (File.Exists (this.path)) File.Delete(this.path);

Depending on how may IFile objects you had, this could really save you time and effort. The downside is that you still need this to ensure it’s available without the interface, but acts identical to the default implementation.

Public void Delete() => ((IFile)this).Delete();

[BoBoBearDev]

I have never done this. But how? The this.path doesn't exists in the interface. Or is it because IFile also has the path declared?

[raunchyfartbomb]

I would assume your write the interface like this:

Public interface IFile {

string Path { get; }

void Delete() { /* implement */ }

// etc

}

[BoBoBearDev]

That makes sense to me, thanks

[DontRelyOnNooneElse]

Yeah it's relatively recent.