Is it an abuse of C#10 ?

[voroninp]

After C#10 introduced global using, I found it quite interesting for fixing some generic type parameters which should stay the same for the whole project.

public static class Foo<TGlobal1>
{
    public static class Bar<TGlobal2>
    {
         public class SomeUsefulClass<TOther1, TOther2>
         {
             TGlobal1 Get<TOther1, TOther2>(TGlobal2 global2, TOther1 val1, TOther2 val2)
             {
                 return default;
             }
         }
    }
}

and then you do

global using static Foo1<string>.Foo2<int>;

I think, this might be useful for library authors. However, the names of the classes are somewhat ugly.

[huoyaoyuan]

What's the benefits comparing to simpler syntax then?

[voroninp]

Simple example.

Let's imagine one designs Result<TSuccess, TError> to use functional style for error propagation. And you do not want to constrain TError type, but it's likely that the shape of the error will be the same for the whole project.
If you define Result in a classic way, then clients of that code will be forced to use the pair of types, or inherit from it Result<TScuccess> : Result<TSuccess, string> {}.

However, it's not always desired:

class A<TError> {}
class A<TSuccess, TError> : A<TError>{}
class B : A<string>{}
class B<TSuccess>: A<TSuccess, string>{}

Here B<TSuccess> is not B. One must introduce implicit conversion from former to latter. And sometimes the hierarchy of classes should be fixed/sealed.

You could argue that one can use interfaces for this, but then you have problems with implicit conversions. That's why it is ActionResult<T> instead of IActionResult<T>

So the alternative would be:

public static class Results
{
    public static class HaveErrorOfType<TError>
    {
        public class Result {...}
        
        public class Result<TSuccess> : Result {...}

        // And here you may define utility methods which will be immediately available when 'global using static Results.HaveErrorOfType<string>;' is used.
    }
}

[huoyaoyuan]

It's hard to say abusing in customer code. If there's no undefined behavior, doing anything should be OK.