More comments on generics

re: More comments on generics

Jon Skeet — Mon, 15 Sep 2008 16:31:50 GMT

Firstly, thanks for the book plug - it's always nice to get a mention :)

It sounds like we've been running into similar (but not the same) restrictions in .NET/C# around generics. I blogged my findings when porting Protocol Buffers recently - any comments would be welcome.

http://msmvps.com/blogs/jon_skeet/archive/tags/Protocol+Buffers/default.aspx

Jon

re: More comments on generics

Brennan Falkner — Mon, 22 Sep 2008 00:58:08 GMT

class Blah : IDependencyNode<Figure, OtherList>, IDependencyNode<Blah, AnotherList> { }

class AnotherList : List<Figure>, IDependencyList<Figure>, IDependencyList<Blah> { }

So yeah, I was just thinking about how painful it would be to have to figure out that algorithm.

May I suggest to you..?

using System.Collections.Generic;

interface IDependencyNode<TNode>

where TNode : IDependencyNode<TNode>

{

// IEnumerable<TNode> Dependencies { get; }

}

static class Extensions

{

public static IEnumerable<TNode> TopologicalSort<TNode>(this IEnumerable<TNode> nodes)

where TNode : IDependencyNode<TNode>

{

return null; // algorithm goes here

}

class Figure : IDependencyNode<Figure> { }

class Program

{

static void Main(string[] args)

{

List<Figure> list = new List<Figure>();

list.TopologicalSort(); // compiles fine

}

re: More comments on generics

Kirill Osenkov — Mon, 22 Sep 2008 06:50:23 GMT

Ha-ha, Brennan, you almost make me feel like I'm an architectural astronaut :)

This chunk of code was to demonstrate a limitation of the C# 3.0 type inference engine, and thankfully doesn't come from production code. Also the last paragraph of my post is there on purpose too.

Jon: great blog posts! I've forwarded a link to Mads Torgersen.

Thanks!

Comments on generics

Riaan's Blog — Mon, 29 Sep 2008 05:50:34 GMT

Some good tips on using Genetics http://blogs.msdn.com/kirillosenkov/archive/2008/09/15/more-comments

Kirill Osenkov : More comments on generics

DotNetKicks.com — Wed, 01 Oct 2008 13:52:13 GMT

You've been kicked (a good thing) - Trackback from DotNetKicks.com

re: More comments on generics

John Rusk — Thu, 02 Oct 2008 11:13:33 GMT

Your technique of Process<T>(T instance) plays nicely with extension methods:

E.g. you can write

T Process<T>(this T instance) where T ....

{

// do stuff...

return instance;

}

to get a method which you can call on any T and which will return a strongly typed T.

This can come in handy in fluent APIs, when you want a method that can act on a range of classes in the API, but for which the implementation is the same and the only difference is the strong return type.

re: More comments on generics

Aridane Álamo — Mon, 13 Oct 2008 12:30:11 GMT

Nice article, thanks.

Just one more question, there is anyway to define the base type of a generic in a method?

Something like

public void Update<T>() where T:DataSet {}

re: More comments on generics

Kirill Osenkov — Thu, 23 Oct 2008 05:41:09 GMT

Aridane: yes, it is called Generic Constraints (http://msdn.microsoft.com/en-us/library/d5x73970(VS.80).aspx) and can be used exactly as you typed.

re: More comments on generics

Shalabh Gupta — Sun, 22 Feb 2009 08:47:01 GMT

Amazing Article. Thanks for such a valuable info..