4.2 Literals
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
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.
Legality Rules
Static Semantics
{
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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
{
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If
its expected type is a numeric type, the The
evaluation of a numeric literal
, or the literal
null, yields the represented value.
[In other cases, the effect of evaluating a numeric literal is determined
by the Integer_Literal or Real_Literal aspect that applies (see 4.2.1).] {
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The evaluation of the literal null yields
the null value of the expected type.{
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{
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The evaluation of a
string_literal
that is a
primary
and has an expected type that is a string type,
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.
[In other cases, the effect of evaluating a string_literal
is determined by the String_Literal aspect that applies (see 4.2.1).]{
AI12-0295-1}
{
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For the evaluation of a
string_literal
of
a string 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
of a string type, a
check is made that its lower bound is greater than the lower bound of
the base range of the index type.
The exception Constraint_Error
is raised if either of these checks fails.
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.
Examples
Examples of literals:
3.14159_26536 -- a real literal
1_345 -- an integer literal
'A' -- a character literal
"Some Text" -- a string literal
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
Wording Changes from Ada 83
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
{
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{
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Null now has type
universal_access,
which is similar to other literals.
Null can be used with anonymous
access types.
Wording Changes from Ada 2012
{
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{
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The rules in this subclause are adjusted to allow
for the possibility of user-defined literals. These are fully documented
in the next subclause.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
