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microsoft.public.dotnet.framework

List(Of clsClass1, clsClass2)?

Pieter

7/15/2008 8:41:00 AM

Hi,

A little bit linked to my other question: I thought it was possible to have
generic list which accept multiple types of objects. So a statement as ""Dim
MyList as List(Of clsClass1, clsClass2)" would accept instances of both
clsClass1 and clsClass2.

But, it doesn't work :-) Am I simply wrong, or did I do something wrong?

Thanks a lot in advance,


Pieter


3 Answers

Jon Skeet

7/15/2008 8:52:00 AM

0

On Jul 15, 9:40 am, "Pieter" <pieterNOSPAMcou...@hotmail.com> wrote:
> A little bit linked to my other question: I thought it was possible to have
> generic list which accept multiple types of objects. So a statement as ""Dim
> MyList as List(Of clsClass1, clsClass2)" would accept instances of both
> clsClass1 and clsClass2.
>
> But, it doesn't work :-) Am I simply wrong, or did I do something wrong?

No, it doesn't work. What would the effective type of the indexer be,
or the iterator?

Jon

Pavel Minaev

7/15/2008 12:30:00 PM

0

On Jul 15, 12:40 pm, "Pieter" <pieterNOSPAMcou...@hotmail.com> wrote:
> Hi,
>
> A little bit linked to my other question: I thought it was possible to have
> generic list which accept multiple types of objects. So a statement as ""Dim
> MyList as List(Of clsClass1, clsClass2)" would accept instances of both
> clsClass1 and clsClass2.
>
> But, it doesn't work :-) Am I simply wrong, or did I do something wrong?

If you want a list of related objects, then it is likely that they
should have a common base class (or implement some common interface).

If you _really_ want a typesafe list of unrelated objects (for
example, because ordering is relevant), then you can use the
Either<T1, T2> type from ECMA TR/89 (http://www.ecma-internat...
publications/techreports/E-TR-089.htm):

var list = new List<Either<Class1, Class2>>();
list.Add(new Class1());
list.Add(new Class2());
foreach (var item in list)
{
if (item.IsFirst)
{
Class1 c1 = (Class1)item;
...
}
else if (item.IsSecond)
{
Class2 c2 = (Class2)item;
...
}
}

By the way, please do not use "cls" prefix for your classes - this is
against pretty much all naming conventions in the .NET land. Class
names are supposed to begin with a capital letter, and Hungarian
notation is generally frowned upon, but particularly so for type names.

SurturZ

7/16/2008 1:49:00 AM

0

Cheat and use a List (Of Object) !! ;-)

In your loops then use GetType and CType to process individual members.

(This approach is "wrong" for many reasons, but oh so useful)

--
David Streeter
Synchrotech Software
Sydney Australia


"Pieter" wrote:

> Hi,
>
> A little bit linked to my other question: I thought it was possible to have
> generic list which accept multiple types of objects. So a statement as ""Dim
> MyList as List(Of clsClass1, clsClass2)" would accept instances of both
> clsClass1 and clsClass2.
>
> But, it doesn't work :-) Am I simply wrong, or did I do something wrong?
>
> Thanks a lot in advance,
>
>
> Pieter
>
>
>