Hi all,

I have classes: Unit, Transporter, Bus and Car

Transporter inherits from Unit and Bus and Car inherit from
Transporter.

I want to be able to do
Bus bus = new Bus()
if (bus is Transporter)
{
//....
}

Apparently .net only validates bus is Bus .

How can i do this?

Thanks
Stijn

Hi Tarscher,

Can you check that your class declarations are correct, or post them here?
The following sample will yield "true" for isTransporter.

class Unit { }
class Transporter : Unit { }
class Bus : Transporter { }
class Car : Transporter { }

static void Main(string[] args)
{
Bus bus = new Bus();
bool isTransporter = bus is Transporter;
}

--
Stanimir Stoyanov
http://stoyanoff.info

"Tarscher" <(E-Mail Removed)> wrote in message
news:62493dcf-4d66-420d-80ff-(E-Mail Removed)...
> Hi all,
>
> I have classes: Unit, Transporter, Bus and Car
>
> Transporter inherits from Unit and Bus and Car inherit from
> Transporter.
>
> I want to be able to do
> Bus bus = new Bus()
> if (bus is Transporter)
> {
> //....
> }
>
> Apparently .net only validates bus is Bus .
>
> How can i do this?
>
> Thanks
> Stijn

On 10/30/2008 11:53 AM, Tarscher wrote:
> Hi all,
>
> I have classes: Unit, Transporter, Bus and Car
>
> Transporter inherits from Unit and Bus and Car inherit from
> Transporter.
>
> I want to be able to do
> Bus bus = new Bus()
> if (bus is Transporter)
> {
> //....
> }
>
> Apparently .net only validates bus is Bus .
>
> How can i do this?

What you have should cause the code to go inside the if block. (bus is
Trasporter) evaluates to true in my quick test.

--
Tom Porterfield

> Apparently .net only validates bus is Bus .

And that is the correct answer. Bus is only a Bus
But you can handle a BUS "as" a Unit
so the correct way is
if ( (bus as Transporter) !=null

Correct me if I am wrong, but isn't the 'as' clause a short-hand operation
of

if (bus is Transporter)
return (Transporter) bus;
else
return null;

in which case the 'is' test would return true?

I believe the problem lies in Stijn's declaration of the classes.

--
Stanimir Stoyanov
http://stoyanoff.info

"Ignacio Machin ( .NET/ C# MVP )" <(E-Mail Removed)> wrote in
message
news:21dad7af-85bd-4037-bb36-(E-Mail Removed)...
>
>> Apparently .net only validates bus is Bus .
>
> And that is the correct answer. Bus is only a Bus
> But you can handle a BUS "as" a Unit
> so the correct way is
> if ( (bus as Transporter) !=null

On 30 okt, 19:09, "Peter Duniho" <NpOeStPe...@nnowslpianmk.com> wrote:
> On Thu, 30 Oct 2008 08:53:10 -0700,Tarscher<tarsc...@gmail.com> wrote:
> > Hi all,
>
> > I have classes: Unit, Transporter, Bus and Car
>
> > Transporter inherits from Unit and Bus and Car inherit from
> > Transporter.
>
> > I want to be able to do
> > Bus bus = new Bus()
> > if (bus is Transporter)
> > {
> > //....
> > }
>
> > Apparently .net only validates bus is Bus .
>
> > How can i do this?
>
> As others have pointed out, the code you posted, assuming declarations are *
> actually as you say they are, should result in the condition in the if() *
> statement evaluating as true.
>
> But, that said...the code seems suspect to me. *The relationship between *
> Bus and Transporter is known at compile time. *The expression has no way *
> to _not_ evaluate as true, assuming Bus really does inherit Transporter. *
> So, if you're writing code that checks that condition, there's a good *
> chance you're going about something the wrong way anyway.
>
> Without seeing a full code example that completely describes your design *
> and intent here, it's hard to offer anything more specific than that. *But *
> on the face of it, your code seems flawed, even if it should do what you *
> seem to expect it to do.
>
> Pete

Thanks all for the replies.

Due to a bug in my code true was not returned (I checked something
else in bus against Transporter). The example provided is jus t a
simplification of my code.

Regards,
Stijn

Ignacio Machin ( .NET/ C# MVP ) wrote:
>> Apparently .net only validates bus is Bus .
>
> And that is the correct answer. Bus is only a Bus
> But you can handle a BUS "as" a Unit
> so the correct way is
> if ( (bus as Transporter) !=null

I have to disagree. A bus is also a Transporter (and a Unit based on
the original post). A quick test will show this to be true, and is the
documented behavior for "is".

An is expression evaluates to true if the provided expression is
non-null, and the provided object can be cast to the provided type
without causing an exception to be thrown.
--
Tom Porterfield