> OK so you are saying the elements in the list are subtypes of
> some type... say IEntity?
yes, but you also have to process lists inside these entities, thus
also lists of 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).
no, that's not going to work. C#/VB.NET don't support
co/contra-variance.
So you've to pass in an IList toProcess.
> 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?
correct.
> Or am I off on a tangent?
No you're right. Methods in interfaces with a where restriction are
more strict than the where clause of a method in a
class, they're less flexible, so that's also something to take into account.
> Your way out of this is to remove the parametisation of the interface?
Yes.
I've for example a collection class, CollectionCore<T> which is the
base class for my EntityCollection<T> class. (I use my
own collection class because I need fine-grained control when a method is
called etc.).
I also implement IEntityCollection on EntityCollection<T>, so I can use
it in code which doesn't know the T type, for
example in code which obtains the lists of related entities inside an entity
instance (e.g. a list returned by Customer with
Customer.Orders, Customer.Employees etc.)
The fun part is that you still can write generic code, even without
casting, but you don't need generic types.
FB
>
> -----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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