Ayende @ Rahien

Germán Schuager commented on Emulating Java Enums

Tue, 07 Oct 2008 15:19:18 GMT

How would you map a class with a property of such "enum" type in NHibernate?

Ayende Rahien commented on Emulating Java Enums

Tue, 30 Sep 2008 14:36:57 GMT

This code is for the .NET 2.0, no Func

Fred Hirschfeld commented on Emulating Java Enums

Tue, 30 Sep 2008 14:26:51 GMT

Bruce, The extension version looks very nice and you could improve it slightly by adding a custom attribute to the code that would decorate the enum member: public enum Planet { [PlanetMeasurements(3.303e+23, 2.4397e6)] Mercury, [PlanetMeasurements(4.869e+24, 6.0518e6)] Venus } Then in the extension methods you would simply access these attributes and use their values thus eliminating the need for the switch statements.

Mike Brown commented on Emulating Java Enums

Tue, 30 Sep 2008 13:35:43 GMT

Just realized that my code got mangled by html private readonly Func isRightLayer;

Mike Brown commented on Emulating Java Enums

Tue, 30 Sep 2008 11:11:42 GMT

Quick question. What are your thoughts on using the Func isRightLayer; >

Andrey Shchekin commented on Emulating Java Enums

Tue, 30 Sep 2008 08:25:24 GMT

Good choice. Enums are antipattern for most situations anyway, since they lead to having unextensible switch-by-enum instead of using polymorphism.

Bruce Boughton commented on Emulating Java Enums

Tue, 30 Sep 2008 06:37:40 GMT

I'm a big fan of Java enums and I had a look at emulating their functionality a while ago in both C# 2.0 and C# 3.5: [siliconbea.ch/.../emulating-java-5-enums-in-dotnet](http://siliconbea.ch/technology/2008-06-08/emulating-java-5-enums-in-dotnet/) My C# 2.0 solution uses an inner enum and a class that wraps it (with common functionality in a base class). [siliconbea.ch/.../emulating-java-5-enums-in-dot...](http://siliconbea.ch/technology/2008-06-08/emulating-java-5-enums-in-dotnet-part-2/) My C# 3.5 solution uses extension methods.

Justin Rudd commented on Emulating Java Enums

Tue, 30 Sep 2008 05:10:33 GMT

The C# enum isn't quite a replacement for the Java one. As it is, it can't be serialized. Adding serializable is just one part. You'd also have to implement whatever the equivalent of readObject and writeObject are to ensure the same instance is returned no matter what. It can't be used in a switch statement. You could use the same delegate trick to add methods to get polymorphism like you can with Java enums ( [http://langrsoft.com/articles/enum2.shtml](http://langrsoft.com/articles/enum2.shtml)), but that breaks down pretty quick if you get beyond a few methods.

Matthew Podwysocki commented on Emulating Java Enums

Tue, 30 Sep 2008 03:03:08 GMT

This is why I like F# for this purpose using discriminated unions. Such code as this works perfectly for modeling what was above: #light type WorkType = | Collection | NonCollection type Layer = | First | Second with member x.IsRightLayer(workType) = match (x, workType) with | l, w when l = First && w <> Collection -> true | l, w -> l = Second && w = Collection Then I can use it such as this: let result = Layer.Second.IsRightLayer(WorkType.Collection) Matt

David commented on Emulating Java Enums

Tue, 30 Sep 2008 02:04:56 GMT

Oops, shoulda refreshed before posting :-\

David commented on Emulating Java Enums

Tue, 30 Sep 2008 02:04:17 GMT

How about using extension methods? public static class LayerExtensions { public static bool IsRightLayer(this Layer layer, WorkType workType) { if (layer == Layer.FIRST && workType != WorkType.COLLECTION) return true; return layer == Layer.SECOND && workType == WorkType.COLLECTION; } }

Hendry Luk commented on Emulating Java Enums

Tue, 30 Sep 2008 00:30:02 GMT

Having said that, there's nothing stopping us from implementing it the same way as java counterpart: private static class Layer { public static readonly Layer FIRST = new Layer(); public static readonly Layer SECOND = new Layer(); public boolean IsRightLayer(WorkType type) { if (this == FIRST && type != WorkType.COLLECTION) return true; return this == SECOND && type == WorkType.COLLECTION; } }

Ayende Rahien commented on Emulating Java Enums

Mon, 29 Sep 2008 23:15:08 GMT

Java enums also have state, which extension methods do not have.

Niki commented on Emulating Java Enums

Mon, 29 Sep 2008 22:34:01 GMT

Why don't you just declare an extension method on you enum? private static enum Layer { FIRST, SECOND } private static class LayerExtensions { public static bool isRightLayer(this Layer layer, WorkType type) { if (layer == FIRST && type != WorkType.COLLECTION) return true; return layer == SECOND && type == WorkType.COLLECTION; } } I know it's not the same internally, but the syntax would be more or less the same.