Reserved Identifier - Reserved Words and Language Independence

Reserved Words and Language Independence

Microsoft’s .NET Common Language Infrastructure (CLI) specification allows code written in 40+ different programming languages to be combined together into a final product. Because of this, identifier/reserved word collisions can occur when code implemented in one language tries to execute code written in another language. For example, a Visual Basic.NET library may contain a class definition such as:

' Class Definition of This in Visual Basic.NET: Public Class this ' This class does something... End Class

If this is compiled and distributed as part of a toolbox, a C# programmer, wishing to define a variable of type “this” would encounter a problem: 'this' is a reserved word in C#. Thus, the following will not compile in C#:

// Using This Class in C#: this x = new this; // Won't compile!

A similar issue arises when accessing members, overriding virtual methods, and identifying namespaces.

In order to work around this issue, the specification allows the programmer to (in C#) place the at-sign before the identifier which forces it to be considered an identifier rather than a reserved word by the compiler.

// Using This Class in C#: @this x = new @this; // Will compile!

For consistency, this usage is also permitted in non-public settings such as local variables, parameter names, and private members.