Visual Basic .NET Language Extension methods Creating an extension method
Example
Extension methods are useful to extend the behaviour of libraries we don't own.
They are used similar to instance methods thanks to the compiler's syntactic sugar:
Sub Main()
Dim stringBuilder = new StringBuilder()
'Extension called directly on the object.
stringBuilder.AppendIf(true, "Condition was true")
'Extension called as a regular method. This defeats the purpose
'of an extension method but should be noted that it is possible.
AppendIf(stringBuilder, true, "Condition was true")
End Sub
<Extension>
Public Function AppendIf(stringBuilder As StringBuilder, condition As Boolean, text As String) As StringBuilder
If(condition) Then stringBuilder.Append(text)
Return stringBuilder
End Function
To have a usable extension method, the method needs the Extension attribute and needs to be declared in a Module.
