checking object is of type parent class

[Tarscher]

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

[Stanimir Stoyanov]

Re: checking object is of type parent class

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" <tarscher@gmail .comwrote in message
news:62493dcf-4d66-420d-80ff-4e542383602b@v2 8g2000hsv.googl egroups.com...

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

[Tom Porterfield]

Re: checking object is of type parent class

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

[Peter Duniho]

Re: checking object is of type parent class

On Thu, 30 Oct 2008 08:53:10 -0700, Tarscher <tarscher@gmail .comwrote:

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

[Ignacio Machin ( .NET/ C# MVP )]

Re: checking object is of type parent class

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

[Stanimir Stoyanov]

Re: checking object is of type parent class

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 )" <ignacio.machin @gmail.comwrote in
message
news:21dad7af-85bd-4037-bb36-35aca79e775c@34 g2000hsh.google groups.com...

>

>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

[Tarscher]

Re: checking object is of type parent class

On 30 okt, 19:09, "Peter Duniho" <NpOeStPe...@nn owslpianmk.comw rote:

On Thu, 30 Oct 2008 08:53:10 -0700,Tarscher<t arsc...@gmail.c omwrote:

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

[Tom Porterfield]

Re: checking object is of type parent class

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