Extension method: Difference between revisions

Revision as of 12:44, 5 January 2008

Revision as of 13:10, 5 January 2008

Line 43:

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

==Extension methods and Instance methods==

==The versioning problem==

In C# 3.0, both an instance method as well as an extension method with the same signature can exist for a class. In such a scenario, the instance method is preferred over the extension method. Neither the compiler nor the [[Microsoft Visual Studio]] IDE warns about the naming conflict. Consider this C# code:

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 stringvoid GetAlphabet() //When this AlphabetMakermethod am)is implemented,

{ //it will shadow the implementation

{

Console.WriteLine("abc"); //in the ExtensionMethods class.

return "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

}

}

</source>

static class ExtensionMethods

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

{

static public stringvoid GetAlphabet(this AlphabetMaker am) //This will only be called

{ //if there is no instance

{

Console.WriteLine("ABC"); //method with the same signature.

return "abc";

}

}

</source>

Result with the instance method not implemented:

The same code using AlphabetMaker now returns a different result:

ABC

<source lang="csharp">

AlphabetMaker am = new AlphabetMaker();

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

</source>

Result with the instance method implemented:

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

abc

==See also==