C#, Generics and casting

[krahenbuhl]

Dear All,

I've a question related to Generics and casting in c# 2.0.
I've a class called Client which implements interface IClient.
I'd like to do:

LinkedList<Client> clients;
public LinkedList<IClient> getClients()
{
return clients;
}

but I got a casting error at compile time (even if the casting is
explicitly given). How should I do to get my list of IClient ?

Regards,

Greg

 

[Marc Gravell]

Just becase Client : IClient, it does not follow that List<Client> :
List<IClient>; as a consequence, you can't quite do what you want to here.

One option is to create a new linked list, and then populate that using
clients (not via the ctor, but manually). It really depends whether it is
critical that this is the *same list*, rather than the same contents. If so,
the only way is to declare clients as List<IClient> and cast appropriately
when you need an actual Client (rather than IClient). Or even better, just
work with IClient throughout.

The reason is that otherwise a caller could declare SomeClass : IClient,
call getClients(), and then add a SomeClass to the list; this would compile,
but would blow up at runtime as the actual clients variable cannot contain
SomeClass; better to blow up at compile time - like it is now.

Marc

 

[Stoitcho Goutsev \(100\)]

Why don't you declare the list as LinkedList<IClient> instead?

 

[krahenbuhl]

Why don't you declare the list as LinkedList<IClient> instead?

I could (and that's what I did), but then when iterating in the list I
need to cast my IClient in Client, which is not very nice

Cheers,

Greg

 

[=?iso-8859-1?Q?Lasse=20V=e5gs=e6ther=20Karlsen?=]

I could (and that's what I did), but then when iterating in the list I
need to cast my IClient in Client, which is not very nice

Cheers,

Greg

Why do you need to cast to the class type? Why not implement an interface
that gives you access to the pieces you want?