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10.3.4 String Types

The value of a variable may be restricted to a list of string literals. The restricted list of string literals is given in a string type declaration.

Here is an example of a string type declaration:

type OS is ("NT, "nt", "Unix", "Linux", "other OS");

Variables of a string type are called typed variables; all other variables are called untyped variables. Typed variables are particularly useful in case constructions (see 10.3.8 case Constructions).

A string type declaration starts with the reserved word type, followed by the name of the string type (case-insensitive), followed by the reserved word is, followed by a parenthesized list of one or more string literals separated by commas, followed by a semicolon.

The string literals in the list are case sensitive and must all be different. They may include any graphic characters allowed in Ada, including spaces.

A string type may only be declared at the project level, not inside a package.

A string type may be referenced by its name if it has been declared in the same project file, or by its project name, followed by a dot, followed by the string type name.