You need an explicit cast to make sure the compiler knows what you're trying to do:
IComparer<U> comparer = (IComparer<U>)new ELementComparer(); Instead of: ELementComparer comparer = new ELementComparer(); Good luck, Paul -----Original Message----- From: Discussion of advanced .NET topics. [mailto:[EMAIL PROTECTED] On Behalf Of Paul Cowan Sent: Wednesday, January 25, 2006 15:34 To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM Subject: Re: [ADVANCED-DOTNET] Generics Comiler error/headache I've implemented an interface which all objects that need ordered will implement. I'm still having problems. Here is a break down of my code: I have an IOrderedChild interface: public interface IOrderedChild { int Index { get; set; } } A Question Element that implements IOrderedChild public class QuestionElement : DBObjectBase, IOrderedChild { public int Index { get { return _index; } set { _index = value; } } } I have a Set class that I reads as follows: public class Set<T, U> : IEnumerable where T : IEnumerable, ICollection, ISet where U : DBObjectBase, IOrderedChild { private List<U> _items; public Set(T list) { _items = new List<U>(); IEnumerator listEnumerator = list.GetEnumerator(); while (listEnumerator.MoveNext()) _items.Add((U)listEnumerator.Current); } public Set(T list, bool sort): this(list) { ELementComparer comparer = new ELementComparer(); _items.Sort(comparer); } } The comparer looks like this: public class ELementComparer : IComparer<IOrderedChild> { int IComparer<IOrderedChild>.Compare(IOrderedChild x, IOrderedChild y) { return (x.Index > y.Index) ? 1 : (x.Index < y.Index) ? -1 : 0; } } This will simply not compile. I get the cannot convert error. I'm going mad. I really wanted to derive a new class from Set that would have the extra constraint on U and put the overloaded constructor in the derived class. Thanks for helping Paul [EMAIL PROTECTED] >From: Ryan Heath <[EMAIL PROTECTED]> >Reply-To: "Discussion of advanced .NET topics." ><ADVANCED-DOTNET@DISCUSS.DEVELOP.COM> >To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM >Subject: Re: [ADVANCED-DOTNET] Generics Comiler error/headache >Date: Wed, 25 Jan 2006 15:13:10 +0100 > >Hi Paul Cowan, > >you could also implement an IComparable<> on your QuestionElement class > >class QuestionElement : IComparable<QuestionElement> >{ >... > int IComparable<QuestionElement>.CompareTo(QuestionElement other) > { > return Comparer<int>.Default.Compare(this.Index, other.Index); > } >} > >by then you do not need to specify a Comparer for the items.Sort function > >BTW >there is a design flaw in your case: by using ElementComparer you are >saying more or less that U *is* a QuestionElement (or descendant of) >... So why is U a generic parameter? > >HTH >// Ryan > >On 1/25/06, Paul Cowan <[EMAIL PROTECTED]> wrote: > > U is a parameterized type I am passing into the class. > > > > It still will not compile. > > > > Thanks > > > > > > > > [EMAIL PROTECTED] > > > > > > > > > > > > >From: Paul van Brenk <[EMAIL PROTECTED]> > > >Reply-To: "Discussion of advanced .NET topics." > > ><ADVANCED-DOTNET@DISCUSS.DEVELOP.COM> > > >To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM > > >Subject: Re: [ADVANCED-DOTNET] Generics Comiler error/headache > > >Date: Wed, 25 Jan 2006 13:57:23 +0100 > > > > > >Your ElementComparar is defined for the specific type QuestionElement, > > >so downcasting it to the more generic type won't work. > > > > > >This code should compile: > > > > > >List<QuestionElement> _items; > > > > > >public Set(T list) > > >{ > > >_items = new List<QuestionElement>(); > > >//code to load collection > > >ElementComparer comparer = new ElementComparer(); > > >_items.Sort(comparer); //WON'T COMPILE > > >} > > > > > > > > > > > >-----Original Message----- > > >From: Discussion of advanced .NET topics. > > >[mailto:[EMAIL PROTECTED] On Behalf Of Paul Cowan > > >Sent: Wednesday, January 25, 2006 13:49 > > >To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM > > >Subject: [ADVANCED-DOTNET] Generics Comiler error/headache > > > > > >I am trying to do a custom sort on using the following comparer: > > > > > >public class ElementComparer : IComparer<QuestionElement> > > >{ > > >public int Compare(QuestionElement x, QuestionElement y) > > >{ > > >return (x.Index > y.Index) ? 1 : (x.Index < y.Index) ? -1 : > > >0; > > >} > > >} > > > > > >I have the following code in the constructor of another object: > > > > > >Then in the constructor of another class, I am trying to sort on a > > >List<U> like this: > > > > > >public Set(T list) > > >{ > > >_items = new List<U>(); > > >//code to load collection > > >ElementComparer comparer = new ElementComparer(); > > >_items.Sort(comparer); //WON'T COMPILE > > >} > > > > > >The compiler error is cannot convert ElementComparer to > > >IComparer<U>. What am I doing wrong. > > > > > >Thanks > > > > > >Paul > > > > > >=================================== > > >This list is hosted by DevelopMentor(r) http://www.develop.com > > > > > >View archives and manage your subscription(s) at > > >http://discuss.develop.com > > > > > >=================================== > > >This list is hosted by DevelopMentor(r) http://www.develop.com > > > > > >View archives and manage your subscription(s) at >http://discuss.develop.com > > > > =================================== > > This list is hosted by DevelopMentor(r) http://www.develop.com > > > > View archives and manage your subscription(s) at >http://discuss.develop.com > > > >=================================== >This list is hosted by DevelopMentor(r) http://www.develop.com > >View archives and manage your subscription(s) at http://discuss.develop.com =================================== This list is hosted by DevelopMentor(r) http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com =================================== This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com
