如何在 C# dotnet 中限制多个泛型参数

Question

How do you "restrict" on 2 or more (multiple) placeholders?

public abstract class MyBaseClass<T> : ISomethingElse<T> where T : struct
{
}

Note, T is confined to a "struct", and I've done this several times over the years.

the above works fine

Now I want to create a generic class definition, and I want to put a constraint on T AND K.

public abstract class MyBaseClass<T, K> : ISomethingElse<T, K> where T : struct , K : struct
{
}

the above .. i cannot figure out the magic syntax sugar.

I know "easy".

Answer 1

You need the where keyword twice.

class Foo<T, K>
   where T : struct
   where K : struct
{
}

Those are constraints on type parameters, and the documentation has a lot of useful information on them.

Answer 2

You can restrict multiple generic arguments by including a where constraint for each argument separated by a space. So in your code snippet this would look like the following:

public abstract class MyBaseClass<T, K> : ISomethingElse<T, K> where T : struct where K : struct
{
}

or a more readable version would be:

public abstract class MyBaseClass<T, K> : ISomethingElse<T, K> 
  where T : struct 
  where K : struct
{
}