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--- attached_methods [2018/01/28 17:24] – created wolfgangriedmann
+++ attached_methods [2018/01/28 17:35] – wolfgangriedmann
@@ Line 1: / Line 1: @@
 ====== Attached methods ======
+In Visual Objects, you could define methods to classes where you had no sources and that are defined in other libraries.
+In the .NET Framework this is not possible, but since this is a very powerful language feature, you can use the ''Attached methods'' to attach methods to another class where you have no sources. This works even with system classes and base datatypes ([[everything_object|Everything is an object]]).
+Please look at this code:
+<code>local cString as string
+local cResult as string
+cString := "Hello world!"
+cResult := cString:Left( 5 )</code>
+But the ''System.String'' class has no ''Left()'' method!
+The solution is this one:
+<code>static class StringExtensions
+static method Left( self cString as string, nLen as int ) as string
+local cReturn as string
+if nLen >= cString:Length
+  cReturn := cString
+else
+  cReturn := cString:Substring( 0, nLen )
+endif
+return cReturn</code>
+The secret lies in the first parameter: 'self cString as string''
+If you have defined this attached method in an assembly with a different namespace, this namespace of course must be included by a ''using'' statement