Extension method: Difference between revisions

Revision as of 01:20, 4 January 2008

Revision as of 02:21, 4 January 2008

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</source>

===Extension methods===

The new language feature of extension methods in C# 3.0, however, makes the latter code possible. This approach requires a static class and a static method, as follows:

<source lang="csharp">

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The major difference between extension methods and normal, static helper methods is that static methods calls are [[Polish_notation|prefix notation]], whereas extension methods calls are in [[Infix_notation|infix notation]]. This leads to more readable code when the result of one operation is used for another operation.

;With static methods: <source lang="csharp">HelperClass.Operation2(HelperClass.Operation1(x, arg1), arg2)"</source>

;With extension methods: <source lang="csharp">x.Operation1(arg1).Operation2(arg2)"</source>

In the current implementation, a member method with the same name as an extension method shadows the latter and makes it inaccessible. The IDE ([[Microsoft Visual Studio|Visual Studio]]) also does not warn about the naming conflict.

==The versioning problem==

Instance methods are always preferred over extension methods, even when new instance methods replace previously-existing extension methods. However, Visual Studio gives no warning about naming conflicts. Consider this C# code:

<source lang="csharp">

class AlphabetMaker { }

static class ExtensionMethods

{

static public string GetAlphabet(this AlphabetMaker am)

{

return "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

}

}

</source>

The GetAlphabet extension method can be called in this way:

<source lang="csharp">

AlphabetMaker am = new AlphabetMaker();

Console.WriteLine(am.GetAlphabet()); // output: ABCDEFGHIJKLMNOPQRSTUVWXYZ

</source>

An instance method is then added to the AlphabetMaker class:

<source lang="csharp">

class AlphabetMaker

{

public string GetAlphabet()

{

return "abc";

}

}

</source>

The same code using AlphabetMaker now returns a different result:

<source lang="csharp">

AlphabetMaker am = new AlphabetMaker();

Console.WriteLine(am.GetAlphabet()); // output: abc

</source>

The new instance method has replaced the extension method, but the Visual Studio compiler gives no indication that a naming conflict exists.

==See also==