Overview of Ada 2022
7.13 Getting the representation of an enumeration value
It has long been possible,
with Ada, to define non-default numeric values for an enumeration type,
using a representation clause, as in:
type Status is (Off, Ready, On);
for Status use (Off => 1, Ready => 2, On => 4);
for interfacing to
hardware where one, and only one, of a group of three bits should be
set. It was not possible to subsequently query what numeric value represented
a given enumeration literal, or vice versa, though. This may have been
to discourage users from adopting a C mentality of thinking in terms
of the numeric values. But to save the user from workarounds, typically
involving Unchecked_Conversion, Ada 2022 (via
Getting the representation
of an enumeration value AI12-0237)
provides attribute 'Enum_Rep to return the number representing a given
enumeration literal, and 'Enum_Val to return the enumeration literal
represented by a given number (see RM
13.4).
Thus:
My_Status : Status := ...;
Rep : Integer;
begin
Rep := Status'Enum_Rep (My_Status);
My_Status := Status'Enum_Val (Rep);
© 2021, 2022 Jeff Cousins
