In computer programming languages, a reserved word is a word which has a special grammatical meaning to a language and cannot be used as an identifier in that language. The NASA Columbia Supercomputer. ... A programming language is an artificial language that can be used to control the behavior of a machine, particularly a computer. ... For the topic in theoretical computer science, see Formal grammar Grammar is the study of rules governing the use of language. ... Identifiers (IDs) are lexical tokens that name entities. ...

For instance, in SQL, a user cannot be called "group" because the word group is used to indicate that an identifier refers to a group, not a user. Such a word is a keyword; it is because its use is restricted that it is also a reserved word. SQL (IPA: or IPA: ), commonly expanded as Structured Query Language, is a computer language designed for the retrieval and management of data in relational database management systems, database schema creation and modification, and database object access control management. ... In computer science, a keyword is an identifier which indicates a specific command. ...

Sometimes the specification for a programming language will have reserved words that are intended for possible use in future versions. In Java, const and goto are reserved words — they have no meaning in Java but they also cannot be used as identifiers. By "reserving" the terms, they can be implemented in future versions of Java, if desired, without "breaking" older Java source code. Java is a programming language originally developed by Sun Microsystems and released in 1995. ... Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. ...

Reserved words and language independence

(See also: Language-independent_specification) A language-independent specification (LIS) is a programming language specification providing a common interface usable for defining semantics applicable toward arbitrary language bindings; in other words, LISs are language-agnostic. ...

In .NET's Common Language Specification, all languages must provide a mechanism for using public identifiers that are reserved words in that language. To see why this is necessary, suppose we defined a class in VB.NET as follows: The Microsoft . ... Visual overview of the Common Language Infrastructure (CLI) The Common Language Infrastructure (CLI) is an open specification developed by Microsoft that describes the executable code and runtime environment that form the core of the Microsoft . ... Visual Basic . ...

 Public Class this End Class  

Then, we compile this class into an assembly and distribute it 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#. The following will not compile in C#: In the Microsoft . ... The title given to this article is incorrect due to technical limitations. ... In many object-oriented programming languages, this (or self) is a keyword which is used to refer to the object on which the currently executing method has been invoked. ... A syntax error refers to a mistake in a statements syntax. ...

 this x = new this();  

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

In C#, placing the at-sign before the identifier, will force it to be considered an identifier rather than a reserved word by the compiler. The at-sign is not considered part of the identifier.

 @this x = new @this();  

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