Does ReadOnlyCollect ion<T> implement IList<T> ?

[Lucian Wischik]

Does ReadOnlyCollect ion<T> really implement IList<T>, like it claims
to do? ...
When I right-click on ReadOnlyCollect ion and look at its definition,
it says this:

public class ReadOnlyCollect ion<T>
: IList<T>,IColle ction<T>,IEnume rable<T> ...

However, the following code fails its assertion check:

List<string> xs = new List<string>();
ReadOnlyCollect ion<string> ro = new ReadOnlyCollect ion<string>(xs) ;
IList<string> il = ro as IList<string>;
Debug.Assert(il != null);

I don't understand how this is possible. If ReadOnlyCollect ion<T>
claims to implement IList<T>, then I should be able to cast to it,
shouldn't I?
In a similar vein, the following code fails to compile because, it
claims, ReadOnlyCollect ion<string> doesnt implement the Insert method.
How is this possible? Insert is part of IList<T>, which
ReadOnlyCollect ion<T> inherits from, so it should be there!

ro.Insert(0,"he llo");

I'm asking these questions because I want to create my own
wrapper-class, similar to how ReadOnlyCollect ion is a wrapper around
an IList. I need to understand which interfaces I should declare
myself as providing. And so I need to understand why
ReadOnlyCollect ion declares that it supports the interfaces it does,
and how.

I wonder if ReadOnlyCollect ion really does implement those interfaces,
but somehow *hides* the Insert method &c.? How is this done in C#? The
documentation specifically says that methds from interfaces must be
public, so I don't know.
--
Lucian

[Jon Skeet [C# MVP]]

Lucian Wischik <lu***@wischik. com> wrote:

Does ReadOnlyCollect ion<T> really implement IList<T>, like it claims
to do? ...
When I right-click on ReadOnlyCollect ion and look at its definition,
it says this:

public class ReadOnlyCollect ion<T>
: IList<T>,IColle ction<T>,IEnume rable<T> ...

However, the following code fails its assertion check:

List<string> xs = new List<string>();
ReadOnlyCollect ion<string> ro = new ReadOnlyCollect ion<string>(xs) ;
IList<string> il = ro as IList<string>;
Debug.Assert(il != null);
Could you post a short but complete program that demonstrates that?
Here's one which seems to go against it:

using System;
using System.Collecti ons.Generic;
using System.Collecti ons.ObjectModel ;

class Test
{
static void Main()
{
List<string> xs = new List<string>();
ReadOnlyCollect ion<string> ro =
new ReadOnlyCollect ion<string>(xs) ;
IList<string> il = ro as IList<string>;
Console.WriteLi ne (il != null);
}
}

That prints out "True" as expected.
In a similar vein, the following code fails to compile because, it
claims, ReadOnlyCollect ion<string> doesnt implement the Insert method.
How is this possible? Insert is part of IList<T>, which
ReadOnlyCollect ion<T> inherits from, so it should be there!

ro.Insert(0,"he llo");
No, it shouldn't - ReadOnlyCollect ion implements IList<T>.Insert
explicitly, so it's only "there" when you're using the
ReadOnlyCollect ion as an IList<T>. In other words, you can do:

((IList<T>)ro). Insert (0, "hello");
I wonder if ReadOnlyCollect ion really does implement those interfaces,
but somehow *hides* the Insert method &c.? How is this done in C#? The
documentation specifically says that methds from interfaces must be
public, so I don't know.

Search for "explicit interface implementation" . Basically, instead of:

public void MethodName(...) ;

you do

void InterfaceName.M ethodName(...);

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Lucian Wischik]

Jon Skeet [C# MVP] <sk***@pobox.co m> wrote:

... Search for "explicit interface implementation" .
Okay, I understand now. Thanks for the prompt and helpful answer.

Could you post a short but complete program that demonstrates that?

No -- it was a mistake on my part, caused by stopping the debugger AT
the cast rather than after it.

--
Lucian