如何将值传递给C＃泛型？

Question

In C++ templates have the feature that you can pass a value as the argument to the template of a function . How can I do the same in C#?

For instance, I want to do something similar to the following:

template <unsigned n> struct Factorial {
     enum { 
        result = n * Factorial<n - 1>::result;
     };
};
template <> struct Factorial<0> {
      enum {
        result = 1;
      };
};

but in C#. How can I do this?

By the way, my actual need for them involves generating classes on demand (with a few static values changed), so the presented code is just an example.

Answer 1

C# generics are not like C++ templates in that way. They only work with types and not values.

Answer 2

but in C#. How can I do this?

By the way, my actual need for them involves generating classes on demand (with a few static values changed), so the presented code is just an example.

As Daniel explained , this is not possible via generics.

One potential alternative is to use T4 Templates . Depending on your needs, you could potentially generate your classes based off the templates at compile time, which sounds like it might meet your needs.

Answer 3

You are trying to make the compiler do stuff that your code should do at runtime.

Yes, this is possible in C++. In C#, It is not. The equivalent of your code in C# would be:

public class Factorial
{
    public static ulong Compute(ulong n)
    {
        if (n == 0)
            return 1;
        return n * Factorial.Compute(n - 1);
    }
}

Note that, while static code is already a bad violation of the OOP principle (but sometimes necessary), using value-based templates is even worse. Your types should depend on other types, which is possible using generics. They should not depend on concrete values.