Scope and Visibility

Scope

The scope of an identifier is a part of the program in which the identifier can be used to access its object. There are different categories of scope, which depends on how and where identifiers are declared:

Place of declaration	Scope
Identifier is declared in the declaration of a program, function, or procedure	Scope extends from the point where it is declared to the end of the current block, including all blocks enclosed within that scope. Identifiers in the outermost scope (file scope) of the main unit are referred to as globals, while other identifiers are locals.
Identifier is declared in the interface section of a unit	Scope extends the interface section of a unit from the point where it is declared to the end of the unit, and to any other unit or program that uses that unit.
Identifier is declared in the implementation section of a unit, but not within the block of any function or procedure	Scope extends from the point where it is declared to the end of the unit. The identifier is available to any function or procedure in the unit.

Visibility

The visibility of an identifier is that region of the program source code from which legal access to the identifier’s associated object can be made.

Scope and visibility usually coincide, though there are circumstances under which an object becomes temporarily hidden by the appearance of a duplicate identifier, i.e. the object still exists but the original identifier cannot be used to access it until the scope of the duplicate identifier is ended.

Technically, visibility cannot exceed scope, but scope can exceed visibility.

Want more examples and libraries?
Find them on