Ada Programming/Attributes/'Enum Val

This language feature has been introduced in Ada 2022.

Description

Return the enumeration literal represented by a given number.

For every enumeration subtype S, S'Enum_Val denotes a function with the following spec:

function S'Enum_Val (Arg : <Universal_Integer>) return S'Base;

The function returns the enumeration value whose representation matches the argument, or raises Constraint_Error if no enumeration literal of the type has the matching value. This will be equal to the value of the Val attribute in the absence of an enumeration representation clause. This is a static attribute (i.e., the result is static if the argument is static).

Example

type Enum_Type is (Enum1, Enum2, Enum3);

pragma Assert (Enum_Type'Enum_Val(0) = Enum1);  -- OK

See also

Wikibook

• Ada Programming
• Ada Programming/Attributes
• Ada Programming/Attributes/'Enum_Rep

Ada Reference Manual

• 13.4: Enumeration Representation Clauses ^[Annotated]
• Annex K: Language-Defined Attributes ^[Annotated]

Ada 2022 Overview

• 7.13 Getting the representation of an enumeration value

External links

GNAT Reference Manual > Implementation Defined Attributes > Enum_Val