Generic type in generic collection

问题

I have generic type that looks like:

public class GenericClass<T, U> where T : IComparable<T>
{
    // Class definition here
}

I then have a collection of these instances. What is the cleanest way to pass through the type constraints?

public class GenericCollection<V> where V : GenericClass<T, U> // This won't compile
{
    private GenericClass<T, U>[] entries;

    public V this[index]
    {
        get{ return this.entries[index]; }
    }
}

Is there perhaps a better way to design this? I think that specifying

GenericCollection<T, U, V> where V : GenericClass<T, U>

seems awkward. Might be my only option though....

回答1:

When creating a generic class, all generic type parameters of all objects used in all members of the generic class must be resolvable at compile time.

You can have type parameters that are specific instances of other generic types - for example:

public class GenericCollection<T> where T : GenericClass<int, string> { ... }

But if you want the type parameters of GenericClass to be generic themselves, then all of those types need to be part of the class declaration, as you've written:

GenericCollection<T, U, V> where V : GenericClass<T, U>

Sorry if it seems awkward, but that's your only option.

回答2:

I think the collection will need the same constraints as GenericClass:

public class GenericCollection<T, U> where T : IComparable<T>
{
    private GenericClass<T, U>[] entries;
}

回答3:

I think your solution is

public class GenericClass<T, U> where T : IComparable<T>
{
     // Class definition here
}

public class GenericCollection<T,U>  where T : IComparable<T>
{
     private GenericClass<T, U>[] entries;
     public GenericClass<T, U> this[int index]
      {
         get{ return this.entries[index]; }
      }
}

回答4:

I think this is what you really want..

    class g<t, u> where t : IComparable<t>
{
}

class gc<t, u>
{
    private g<t, u>[] entries;

    public g<t, u> this[int index]
    {
        get { return this.entries[index]; }
    }
}

回答5:

you haven't declared it as a class!

public class GenericCollection<V>

来源：https://stackoverflow.com/questions/2560902/generic-type-in-generic-collection

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