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An enumeration_type_definition defines an enumeration type.
Syntax
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enumeration_type_definition ::=
(enumeration_literal_specification
{, enumeration_literal_specification})
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enumeration_literal_specification ::=
defining_identifier | defining_character_literal
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defining_character_literal ::= character_literal
Legality Rules
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The defining_identifiers and defining_character_literals listed in an
enumeration_type_definition shall be distinct.
Static Semantics
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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.
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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.
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The predefined order relations between values of the enumeration type
follow the order of corresponding position numbers.
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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 section 8.6 The Context of Overload Resolution.
Dynamic Semantics
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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.
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When called, the parameterless function associated with an enumeration
literal returns the corresponding value of the enumeration type.
NOTES
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(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 section 4.7 Qualified Expressions.
Examples
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Examples of enumeration types and subtypes:
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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
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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