Using Statement with Generics: using ISet<> = S

问题:

Since I am using two different generic collection namespaces (System.Collections.Generic and Iesi.Collections.Generic), I have conflicts. In other parts of the project, I am using both the nunit and mstest framework, but qualify that when I call Assert I want to use the nunit version by

using Assert = NUnit.Framework.Assert;

Which works great, but I want to do the same thing with generic types. However, the following lines do not work

using ISet = System.Collections.Generic.ISet;
using ISet<> = System.Collections.Generic.ISet<>;

Does anyone know how to tell .net how to use the using statement with generics?

回答1:

I think you're better off aliasing the namespaces themselves as opposed to the generic types (which I don't think is possible).

So for instance:

using S = System.Collections.Generic;
using I = Iesi.Collections.Generic;

Then for a BCL ISet<int>, for example:

S.ISet<int> integers = new S.HashSet<int>();

回答2:

Unfortunately, the using directive does not do what you want. You can say:

using Frob = System.String;

and

using ListOfInts = System.Collections.Generic.List<System.Int32>;

but you cannot say

using Blob<T> = System.Collections.Generic.List<T>

or

 using Blob = System.Collections.Generic.List

It's a shortcoming of the language that has never been rectified.

回答3:

The only way you can alias a generic type is to specialize it as follows.

using IntSet = System.Collections.Generic.ISet<int>;

You can not alias an open generic type as you have done in your example:

using MySet = System.Collections.Generic.ISet<>;

回答4:

Your alias name is the same as the class name itself, so you still have ambiguity, just as if you had a using for each namespace. Give the alias of the class a different name, i.e.:

using FirstNamespace;
using OtherObject = SecondNamespace.MyObject;

public class Foo
{
    public void Bar()
    {
        MyObject first = new MyObject;//will be the MyObject from the first namespace
        OtherObject second = new OtherObject;
    }
}

回答5:

You can alias a class doing :

using Test = NameSpace.MyClass;

Only if the class is NOT generic.

回答6:

In some cases you can go with inheritance:

    public class MyList<T1, T2> : List<Tuple<IEnumerable<HashSet<T1>>, IComparable<T2>>> { }

    public void Meth()
    {
        var x = new MyList<int, bool>();
    }