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In computer programming, scope is an enclosing context where values and expressions are associated. The scope resolution operator helps to identify and specify the context to which an identifier refers, particularly by specifying a namespace or class. The specific uses vary across different programming languages with the notions of scoping.
A namespace in computer science (sometimes also called a name scope) is an abstract container or environment created to hold a logical grouping of unique identifiers or symbols (i.e. names). An identifier defined in a namespace is associated only with that namespace. The same identifier can be independently defined in multiple namespaces.
Static name resolution catches, at compile time, use of variables that are not in scope; preventing programmer errors. Languages with dynamic scope resolution sacrifice this safety for more flexibility; they can typically set and get variables in the same scope at runtime. For example, in the Python interactive REPL:
In Python, auxiliary variables in generator expressions and list comprehensions (in Python 3) have expression scope. In C, variable names in a function prototype have expression scope, known in this context as function protocol scope. As the variable names in the prototype are not referred to (they may be different in the actual definition ...
In computer programming, variable shadowing occurs when a variable declared within a certain scope (decision block, method, or inner class) has the same name as a variable declared in an outer scope. At the level of identifiers (names, rather than variables), this is known as name masking.
A name's linkage is related to, but distinct from, its scope. The scope of a name is the part of a translation unit where it is visible. For instance, a name with global scope (which is the same as file-scope in C and the same as the global namespace-scope in C++) is visible in any part of the file.
The Python programming language includes extensive support for creating and manipulating symbol tables. [5] Properties that can be queried include whether a given symbol is a free variable or a bound variable , whether it is block scope or global scope , whether it is imported, and what namespace it belongs to.
To distinguish a fully qualified name from a regular name, C++, Tcl, Perl and Ruby use two colons (::), and Java uses dots (.), as does Visual Basic .NET. [3] and C#. [4]In Java, ActionScript, [5] and other object-oriented languages the use of the dot is known as "dot syntax". [6]