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3.5.1 Enumeration Types
1
An
enumeration_type_definition
defines an enumeration type.
Syntax
2
enumeration_type_definition
::=
(
enumeration_literal_specification {,
enumeration_literal_specification})
3
enumeration_literal_specification
::= defining_identifier |
defining_character_literal
4
defining_character_literal
::= character_literal
Legality Rules
5
The defining_identifiers
and defining_character_literals
listed in an enumeration_type_definition
shall be distinct.
Static Semantics
6
Each
enumeration_literal_specification
is the explicit declaration of the corresponding
enumeration literal:
it declares a parameterless function, whose defining name is the
defining_identifier
or
defining_character_literal, and
whose result type is the enumeration type.
7
Each enumeration literal corresponds to a distinct
value of the enumeration type, and to a distinct position number.
The
position number of the value of the first listed enumeration literal
is zero; the position number of the value of each subsequent enumeration
literal is one more than that of its predecessor in the list.
8
The predefined order relations between values
of the enumeration type follow the order of corresponding position numbers.
9
If the same
defining_identifier
or
defining_character_literal is
specified in more than one
enumeration_type_definition,
the corresponding enumeration literals are said to be
overloaded.
At any place where an overloaded enumeration literal occurs in the text
of a program, the type of the enumeration literal has to be determinable
from the context (see
8.6).
Dynamic Semantics
10
The
elaboration of an
enumeration_type_definition
creates the enumeration type and its first subtype, which is constrained
to the base range of the type.
11
When called, the parameterless function associated
with an enumeration literal returns the corresponding value of the enumeration
type.
12
22 If an enumeration literal
occurs in a context that does not otherwise suffice to determine the
type of the literal, then qualification by the name of the enumeration
type is one way to resolve the ambiguity (see 4.7).
Examples
13
Examples of
enumeration types and subtypes:
14
type Day is (Mon, Tue, Wed, Thu, Fri, Sat, Sun);
type Suit is (Clubs, Diamonds, Hearts, Spades);
type Gender is (M, F);
type Level is (Low, Medium, Urgent);
type Color is (White, Red, Yellow, Green, Blue, Brown, Black);
type Light is (Red, Amber, Green); -- Red and Green are overloaded
15
type Hexa is ('A', 'B', 'C', 'D', 'E', 'F');
type Mixed is ('A', 'B', '*', B, None, '?', '%');
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subtype Weekday is Day range Mon .. Fri;
subtype Major is Suit range Hearts .. Spades;
subtype Rainbow is Color range Red .. Blue; -- the Color Red, not the Light
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