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4.2 Literals
1
[
{literal} A
literal represents a value literally, that is, by means of notation
suited to its kind.] A literal is either a
numeric_literal,
a
character_literal, the literal
null, or a
string_literal.
{constant: See also literal} 1.a
Discussion: An enumeration
literal that is an identifier rather
than a character_literal is not
considered a literal in the above sense, because it involves no
special notation ``suited to its kind.'' It might more properly be called
an enumeration_identifier, except
for historical reasons.
Name Resolution Rules
2
{expected type (null literal)
[partial]} The expected type for a literal
null shall be a single access type.
2.a
Discussion: This new wording ("expected
type ... shall be a single ... type") replaces the old "shall be determinable"
stuff. It reflects an attempt to simplify and unify the description of the rules
for resolving aggregates, literals, type conversions, etc. See 8.6,
``The Context of Overload Resolution'' for the details.
3
{expected type (character_literal)
[partial]} {expected profile (character_literal)
[partial]} For a
name
that consists of a
character_literal, either
its expected type shall be a single character type, in which case it is interpreted
as a parameterless
function_call that yields
the corresponding value of the character type, or its expected profile shall
correspond to a parameterless function with a character result type, in which
case it is interpreted as the name of the corresponding parameterless function
declared as part of the character type's definition (see
3.5.1).
In either case, the
character_literal denotes
the
enumeration_literal_specification.
3.a
Discussion: See 4.1.3
for the resolution rules for a selector_name
that is a character_literal.
4
{expected type (string_literal)
[partial]} The expected type for a
primary
that is a
string_literal shall be
a single string type.
Legality Rules
5
A character_literal
that is a name shall correspond
to a defining_character_literal
of the expected type, or of the result type of the expected profile.
6
For each character of a string_literal
with a given expected string type, there shall be a corresponding defining_character_literal
of the component type of the expected string type.
7
A literal
null
shall not be of an anonymous access type[, since such types do not have a null
value (see
3.10)].
7.a
Reason: This is a legality
rule rather than an overloading rule, to simplify implementations.
Static Semantics
8
An integer literal is of type universal_integer.
A real literal is of type universal_real.
Dynamic Semantics
9
{evaluation (numeric literal)
[partial]} {evaluation (null
literal) [partial]} {null
access value} {null pointer:
See null access value} The evaluation
of a numeric literal, or the literal
null, yields the represented
value.
10
{evaluation (string_literal)
[partial]} The evaluation of a
string_literal
that is a
primary yields an array value
containing the value of each character of the sequence of characters of the
string_literal, as defined in
2.6.
The bounds of this array value are determined according to the rules for
positional_array_aggregates
(see
4.3.3), except that for a null string literal,
the upper bound is the predecessor of the lower bound.
11
{Range_Check [partial]}
{check, language-defined (Range_Check)}
For the evaluation of a
string_literal
of type
T, a check is made that the value of each character of
the
string_literal belongs to the
component subtype of
T. For the evaluation of a null string literal,
a check is made that its lower bound is greater than the lower bound
of the base range of the index type.
{Constraint_Error
(raised by failure of run-time check)} The
exception Constraint_Error is raised if either of these checks fails.
11.a
Ramification: The checks
on the characters need not involve more than two checks altogether, since
one need only check the characters of the string with the lowest and
highest position numbers against the range of the component subtype.
12
6 Enumeration literals that are identifiers
rather than character_literals follow the
normal rules for identifiers when used
in a name (see 4.1
and 4.1.3). Character_literals
used as selector_names follow the normal
rules for expanded names (see 4.1.3).
Examples
13
Examples of
literals:
14
3.14159_26536 -- a real literal
1_345 -- an integer literal
'A' -- a character literal
"Some Text" -- a string literal
Incompatibilities With Ada 83
14.a
{incompatibilities with Ada
83} Because character_literals
are now treated like other literals, in that they are resolved using
context rather than depending on direct visibility, additional qualification
might be necessary when passing a character_literal
to an overloaded subprogram.
Extensions to Ada 83
14.b
{extensions to Ada 83}
Character_literals
are now treated analogously to null and string_literals,
in that they are resolved using context, rather than their content; the
declaration of the corresponding defining_character_literal
need not be directly visible.
Wording Changes from Ada 83
14.c
Name Resolution rules for enumeration
literals that are not character_literals
are not included anymore, since they are neither syntactically nor semantically
"literals" but are rather names of parameterless functions.
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