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
2/2
This paragraph was
deleted.{
AI95-00230-01}
{expected type
(null literal) [partial]} The expected
type for a literal null shall be a single access type.
2.a/2
This paragraph
was deleted.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.
7/2
This paragraph was
deleted.{
AI95-00230-01}
{
AI95-00231-01}
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/2
This paragraph
was deleted.Reason: This is a
legality rule rather than an overloading rule, to simplify implementations.
Static Semantics
8/2
{
AI95-00230-01}
An integer literal is of type
universal_integer. A real literal
is of type
universal_real.
The literal null
is of type universal_access. 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.
Extensions to Ada 95
14.d/2
{
AI95-00230-01}
{
AI95-00231-01}
{extensions to Ada 95} Null
now has type universal_access, which is similar to other literals.
Null can be used with anonymous access types.
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