[Proposal] public internal

[JustNrik]

Public exposure, Internal consumption. Classes and Interfaces with this keyword combination are exposed as public members but can't be inherited/implemented outside the assembly, they are for internal consumption only.

[Joe4evr]

So basically, you want InternalImplementationOnly.

[JustNrik]

Yes

[DavidArno]

Difficult to be sure here, as DIMs in C# 8 are still a bit of an unknown, but in theory,

public IInternalImplementationOnly
{
    internal void InternalOnlyImplementationGuard();
}

should cover this already as only internal classes can implement InternalOnlyImplementationGuard. Until we get a release of VS219 that includes DIMs though, it's hard to known if that will really work.

[jnm2]

Duplicate of #485, #1716, #1790.

[JustNrik]

It looks like java 15 is implementing some feature similar to this, sealed classes/interfaces, sealed here meaning that these classes/interfaces can only be inherited/implemented by the types specified by permits keyword. It would be interesting to see how would that work here or be implemented.

I would proprose it as closed/allows.

public closed interface IFoo
    allows Foo
{
    void Bar();
}

So the interface is publicy exposed, but can only be implemented by Foo, no other class/type can implement it. I'm not sure how would this work with interface inheritance but I would guess they would inherit the same restriction or would it have to be explicit? What do you think guys?