Andrés G. Aragoneses [ knocte ] wrote:
> Robert Jordan escribió:
>> Andrés G. Aragoneses [ knocte ] wrote:
>>> Robert Jordan escribió:
>>>> Andrés G. Aragoneses [ knocte ] wrote:
>>>>> Today I've come out with this wish:
>>>>>
>>>>> Dictionary<typeof(T), List<T>> InternalCollection;
>>>>>
>>>>>
>>>>> Of course, the compiler tells me an error, but I would want to know if I
>>>>> can make this kind of collection with C# generics, in order to obtain
>>>>> syntatic sugar and type safety, I mean:
>>>>>
>>>>> //compilation should succeed only if oMyObj is TypeX:T
>>>>> InternalCollection.Add(typeof(TypeX), oMyObj);
>>>>>
>>>>> Any thoughts?
>>>> class FooDictionary<T> : Dictionary<System.Type, T>
>>>> {
>>>> public void Add (T t)
>>>> {
>>>> this [typeof(T)] = t;
>>>> }
>>>> }
>>>>
>>> But that would only allow adding one object:
>>
>> Well, then use that slightly modified Add method:
>>
>> public void Add (T t)
>> {
>> if (t == null)
>> throw new ArgumentNullException ("t");
>> this [t.GetType ()] = t;
>> }
>>
>
> Ok! But if I modify it to use lists, I get a compiler error:
>
> class FooDictionary<T> : Dictionary<Type, List<T>>
> {
> public void Add (List<T> t)
> {
> if (t == null)
> {
> throw new ArgumentNullException("t");
> }
> if (t.Count > 0)
> {
> this[t[0].GetType()] = t;
> }
> }
> }
>
> ...
>
> FooDictionary<mytype> foo = new FooDictionary<mytype>();
> foo.Add(new List<subtypeA>());
>
> Error 11 Argument '1': cannot convert from
> 'System.Collections.Generic.List<subtypeA>' to
> 'System.Collections.Generic.List<mytype>'
>
> However, it should allow it because subtypeA inherits from mytype,
> right? I think I've reached a limitation of .NET generics, which I think
> I read about here[1] :(
This works, at least with MS.NET 2.0 csc:
using System;
using System.Collections.Generic;
class FooDictionary<T> : Dictionary<System.Type, List<T>>
{
public void Add (List<T> t)
{
if (t == null)
throw new ArgumentNullException ("t");
// key is the generic argument of List<T>
this [t.GetType ().GetGenericArguments() [0]] = t;
}
}
class Test
{
static void Main ()
{
FooDictionary<int> d = new FooDictionary<int> ();
d.Add (new List<int> ());
}
}
Robert
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