Generic type constraint complation error

[Lars]

I have a compilation error and do not know how to fix it. This is the
first time I've tried to use a generic type constraint.

What have I done wrong?

public sealed class ClassA : IInput
{
...
}

public class ClassB<Twhere T : IInput
{

public ClassB() {...}

public IInput[] Generate()
{
Engine<Tengine = new Engine<T>();
IInput[] lst = engine.ReadFile (someFileName); <===== ERROR:
return lst;
}
}


ERROR: Cannot implicitly convert type 'T[]' to 'IInput[]'

[Hans Kesting]

Re: Generic type constraint complation error

Lars explained :

I have a compilation error and do not know how to fix it. This is the
first time I've tried to use a generic type constraint.
>
What have I done wrong?
>
public sealed class ClassA : IInput
{
...
}
>
public class ClassB<Twhere T : IInput
{
>
public ClassB() {...}
>
public IInput[] Generate()
{
Engine<Tengine = new Engine<T>();
IInput[] lst = engine.ReadFile (someFileName); <===== ERROR:
return lst;
}
}
>
>
ERROR: Cannot implicitly convert type 'T[]' to 'IInput[]'

The errormessage says is all:
your 'engine.ReadFil e()' method apparently returns a 'T[]' and you are
trying to put that into a 'IInput[]' variable.
Try to use explicit casting (IInput[] lst =
(IInput[])engine.ReadFil e(someFileName) ), although I don't know whether
that will succeed.
If it fails, store the result in a T[] (maybe you can return that?),
create a new IInput[] of the correct size and copy ann values.

Hans Kesting

[Anthony Jones]

Re: Generic type constraint complation error

"Hans Kesting" <news.hansdk@sp amgourmet.comwr ote in message
news:ujRHY$EOJH A.1148@TK2MSFTN GP05.phx.gbl...

Lars explained :

>I have a compilation error and do not know how to fix it. This is the
>first time I've tried to use a generic type constraint.
>>
>What have I done wrong?
>>
> public sealed class ClassA : IInput
> {
> ...
> }
>>
> public class ClassB<Twhere T : IInput
> {
>>
> public ClassB() {...}
>>
> public IInput[] Generate()
> {
> Engine<Tengine = new Engine<T>();
> IInput[] lst = engine.ReadFile (someFileName); <===== ERROR:
>return lst;
> }
> }
>>
>>
>ERROR: Cannot implicitly convert type 'T[]' to 'IInput[]'

>
The errormessage says is all:
your 'engine.ReadFil e()' method apparently returns a 'T[]' and you are
trying to put that into a 'IInput[]' variable.
Try to use explicit casting (IInput[] lst =
(IInput[])engine.ReadFil e(someFileName) ), although I don't know whether
that will succeed.
If it fails, store the result in a T[] (maybe you can return that?),
create a new IInput[] of the correct size and copy ann values.
>

The Engine class need to constrain its T to IInput as well for this to work.
That being the case it would probably be best the ReadFile returns IInput[]
instead of T[] anyway.

--
Anthony Jones - MVP ASP/ASP.NET