OK so you are saying the elements in the list are subtypes of some type...
say IEntity?
And thus the
"// yadda yadda"
Is something like;
Foreach(IEntity orderOrProduct in list)
{
// yadda yadda on orderOrProduct
}
Is thus the problem that .net doesn't realise that (in this example, i.e.
assuming the type parameters are not in parameters on any method of IEntity,
i.e contravaraint parameters I think)....
ISomething<IProduct> is a subtype of ISomething<IEntity> ?
Thus you should be able to simply declare the parameter as
"private void ProcessISomething(ISomething<IEntity> toProcess)"
And dot net accept ISomething<IProduct> as a subtype of ISomething<IEntity>
(given it obeys rules of contra/covariance).
Rather than
"private void ProcessISomething<X>(ISomething<X > toProcess)
Where X : IEntity"
And thus end up constantly parametising methods that really shouldn't need
parametising?
Or am I off on a tangent?
Your way out of this is to remove the parametisation of the interface?
-----Original Message-----
From: Discussion of advanced .NET topics.
[mailto:[EMAIL PROTECTED] On Behalf Of Frans Bouma
Sent: 18 October 2006 11:47
To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
Subject: Re: [ADVANCED-DOTNET] Type declarations in ide....
> Not completely with this.
>
> This bit.....
>
> foreach(IList list in containingLists)
> {
> // yadda yadda
> }
>
> What sort of things are you doing in the "yadda yadda" bit.....
> If you don't know the type of the elements of list you can't
> access them.
>
> If you do know the type of the elements then, the type is known.
processing the items in the list.
Let me give you a real world example: your code receives a
collection of entity classes (which implement an interface) and
you've to sort the complete graph (so containing entities inside these
entities as well) using topology sort.
It's unknown if the collection inside the first entity for example
contains Order entities or products, you also shouldn't
care.
What's great is that if the entities implement an interface, say
IEntity, and the collections implement an interface, say
IEntityCollection, (or IList of you want to), you can solve this with easy
to read code.
If you don't have the interfaces, you will have to deal with the
generics somewhere and it gets so incredibly complex, it's
not fun anymore. The where clauses are impractical to work with, especially
with generic interfaces mixed with generic classes.
> P.S.
>
> I tend to do this with most techniques that are new to me, I
> abuse them to the point where they become impractical.....and
> then I know their limits....I'm just taking generics to an
> extreme in order to get a feel for their practical limits/application.
Ok, well I had that plan once as well :) when I ported my .NET 1.x
o/r core to .NET 2.0 and thought that with one new core
using generics all over the place, it would be simpler, easier to read and
more compact.
That was a mistake. :). The code became so utterly complex, that I
started over, using non-generic interfaces (I Used
generic interfaces in the first attempt) implemented by generic classes. The
end result is readable code and uses generics where
appropriate and doesn't when it's not needed.
IMHO new features like generics are far overrated when you compare
it to readability and simplicity. Code should be so
simple to read it's simply too boring to even be considered 'cool'. If
someone asks you: "Hey man, show me some really awesome code
you wrote lately", and you look at your code and with everything you think:
"this is too boring to show", you're at the right track.
FB
>
> -----Original Message-----
> From: Discussion of advanced .NET topics.
> [mailto:[EMAIL PROTECTED] On Behalf Of Frans Bouma
> Sent: 18 October 2006 10:30
> To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
> Subject: Re: [ADVANCED-DOTNET] Type declarations in ide....
>
> > You'll have to explain with an example.....it's early in
> the morning
> > and my brain isn't up to it.
>
> public class Foo : ISomething
> {
> private List<Bar> _bars;
>
> //... ctor, creation etc.
>
> List<Object> ISomething.GetContainingLists()
> {
> List<Object> toReturn = new List<Object>();
> toReturn.Add(_bars);
> return toReturn;
> }
> }
>
>
> Now, in some other code, an ISomething instance is passed in.
> This can be a Foo instance, but it can also be a FooToo instance:
>
> public class FooToo : ISomething
> {
> private List<BarToo> _bars;
>
> //... ctor, creation etc.
>
> List<Object> ISomething.GetContainingLists()
> {
> List<Object> toReturn = new List<Object>();
> toReturn.Add(_bars);
> return toReturn;
> }
> }
>
>
> So, consuming code, which consumes ISomething looks like:
>
> private void ProcessISomething(ISomething toProcess) {
> List<Object> containingLists = toProcess.GetContainingLists();
>
> // and now what... how to access the lists inside
> containingLists ?
> // that's right, via a non-generic interface. because
> any generic interface
> // would require _at compile time_ the generic type.
> Which is UNKNOWN.
> foreach(IList list in containingLists)
> {
> // yadda yadda
> }
> }
>
> You might think: I can solve this with a helper method:
>
> private void DoProcessing<T>(List<T> toProcess) {
> // yadday yadda
> }
>
> and write ProcessISomething as:
>
> However, how would you use T in this method? You've
> to specify a where clause, and ProcessISomething, how would
> you write that?
>
> See, with generic interfaces, you don't solve this,
> as you then still need a generic type parameter to specify
> _at compile time_ . With NON generic interfaces you solve
> this. That's why non-generic interfaces should be used to
> consume generic code in routines which don't know the type of
> the generic parameter.
>
> Using interfaces is also a way to do generic
> programming, i.e. write a program that can work with multiple
> types. Mixing interfaces and generics, makes things only more
> complicated instead of more usable and readable.
>
> Frans
>
>
>
> >
> > -----Original Message-----
> > From: Discussion of advanced .NET topics.
> > [mailto:[EMAIL PROTECTED] On Behalf Of
> Frans Bouma
> > Sent: 17 October 2006 16:39
> > To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
> > Subject: Re: [ADVANCED-DOTNET] Type declarations in ide....
> >
> > > I agree....its more of an experiment at the
> moment.....and they are
> > > interfaces....just parametised ones.
> >
> > Generic interfaces? Isn't that mitigating the aspect of
> > interfaces?
> > I mean: if you have an instance of Class<T>, and pass that to some
> > code and inside that code you don't know the type of T (this can
> > happen), you can refer to the instance of Class<T> with the
> interface,
> > so your code will become very simple. If you have generic
> interfaces
> > as well, the problem remains and you have to at some point need to
> > know the type of T to get things compiled.
> >
> > This especially creates problems when T has to be of some
> > type, so where clauses have to be added to the method.
> > With an interface you can solve this problem. so I always
> use the rule
> > of thumb: use interfaces to use generic classes in code where you
> > don't know the generic parameter type, and thus keep your
> interfaces
> > non-generic just for this purpose.
> >
> > FB
> >
> > >
> > > -----Original Message-----
> > > From: Discussion of advanced .NET topics.
> > > [mailto:[EMAIL PROTECTED] On Behalf Of
> > Frans Bouma
> > > Sent: 17 October 2006 13:17
> > > To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
> > > Subject: Re: [ADVANCED-DOTNET] Type declarations in ide....
> > >
> > > > A slightly bizarre question....
> > > >
> > > > I've got some generic methods that return generic types,
> > > the problem
> > > > is that sometimes the types get very large...e.h.
> > > >
> > > >
> > > > Foo<Foo<Bar<Foo<Bar>,Foo<Foo>>>> x =
> > > > a.GetFoo<Foo<Bar<Foo<Bar>,Foo<Foo>>>>
> > > > (b);
> > > >
> > > > is there a way of getting the IDE to auto generate the type
> > > > declaration, so I don't spend hours foo'ing and bar'ing.
> > >
> > > I'm not sure if you should continue with this. It
> > makes code
> > > VERY unreadable. Too much of a good is still 'too much' ;)
> > >
> > > You might want to use an interface here and there.
> > >
> > > Frans
> > >
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