通用类和通用方法

Question

class test <T> where T : class
{
    public void Write<T>()
    {
        Console.Write(typeof(T).FullName);
    }
}

In the above class, it is possible to pass in a string for the class ( test<string> Test = new test<string> ) and then int for the method? If so, what is the output? If not, what problems does this cause? I haven't actually tried this, despite using generics (in my own classes) and generic collections, frequently.

The way I write/see generic classes is as follows:

class <T> where T : class
{
    public T Write()
    {
        Console.Write(T.ToString());
    }
}

Answer 1

As it was originally written no you cannot. In order to use different types at different points in the class, you must have multiple generic parameters. It is possible to define a different one at the method level and get your sample to work

class Test<T> where T : class {
  public void Write<U>(U arg1) {
    Console.WriteLine(arg1.ToString());
  }
}

Usage

var t = new Test<string>();
t.Write(42);

As Scott pointed out you can use the same named parameter. Although doing so will cause a warning and generally speaking confuse people. It is much cleaner to have distinct names for all generic parameters currently in scope.

Answer 2

You'll be wanting to declare a type variable in the method separately to the class -

class Test<T> where T : class {

    public void Method<U>(U val) {
        Console.WriteLine(typeof(U).FullName);
    }

}