To extend any class public static class Extensions { public static T DoSomething<T>(this T obj) { //… } } To extend a specific generic class public static NeedExtension<T> DoSomething<T>(this NeedExtension<T> obj) { //… }
Downside of extension methods: clients pre-C#3/VB9 won’t be able to use it as easily. That’s about it as far as I’m concerned – I think the interface-based approach is significantly nicer. You can then mock out your dependencies nicely, and everything is basically less tightly coupled. I’m not a huge fan of class inheritance unless … Read more
To extend an F# module, just create another module with the same name: module Seq = let myMap f s = seq { for x in s do yield f x } Seq. // see your stuff here alongside normal stuff
Consider a class named StringExtensions like so: static class StringExtensions { public static string Truncate(this string value, int maxChars) { return value.Length <= maxChars ? value : value.Substring(0, maxChars) + ” ..”; } } Be sure that whatever namespace you put this class in, you include a using declaration for that namespace. Thus, for a … Read more
This is probably one of those rare cases where it makes sense to use an extern alias. In the properties page for the reference to System.Core (i.e. under References, select System.Core, right-click and select “Properties”), change the “Aliases” value to “global,SystemCore” (or just “SystemCore” if it’s blank to start with). Then in your code, write: … Read more
Perhaps a bit off-topic, but I use a ToDelimitedString extension method which works for any IEnumerable<T>. You can (optionally) specify the delimiter to use and a delegate to perform a custom string conversion for each element: // if you’ve already overridden ToString in your MyClass object… Console.WriteLine(list.ToDelimitedString()); // if you don’t have a custom ToString … Read more
EDIT: The list below applies to C# anonymous types. VB.NET has different rules – in particular, it can generate mutable anonymous types (and does by default). Jared has pointed out in the comment that the naming style is different, too. Basically this is all pretty fragile… You can’t identify it in a generic constraint, but: … Read more
In response to my other answer, Eric Smith correctly notes: “… because it would require implicitly boxing the receiver type parameter …”. Which is what happens anyway, if you do something like this: Func f = 5.ToString; Which is perfectly legal. Thinking about this has led me to a new answer. Try this on for … Read more
The way that extension methods are imported (i.e. a whole namespace at a time) isn’t granular. You can’t import one extension from a namespace without getting all the rest. It’s not immediately obvious from the source code where the method is defined. This is also an advantage – it means you can make your code … Read more
Like so: // you need this once (only), and it must be in this namespace namespace System.Runtime.CompilerServices { [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Method)] public sealed class ExtensionAttribute : Attribute {} } // you can have as many of these as you like, in any namespaces public static class MyExtensionMethods { public static int MeasureDisplayStringWidth ( … Read more