3.3.2 Number Declarations
1
A number_declaration declares
a named number.
1.a
Discussion: {
static}
If
a value or other property of a construct is required to be
static
that means it is required to be determined prior to execution. A
static
expression is an expression whose value is computed at compile time and
is usable in contexts where the actual value might affect the legality
of the construct. This is fully defined in clause
4.9.
Syntax
2
number_declaration ::=
defining_identifier_list :
constant :=
static_expression;
Name Resolution Rules
3
{expected type (number_declaration
expression) [partial]} The
static_expression
given for a
number_declaration is expected
to be of any numeric type.
Legality Rules
4
The
static_expression
given for a number declaration shall be a static expression, as defined
by clause
4.9.
Static Semantics
5
The named number denotes a value of type universal_integer
if the type of the static_expression
is an integer type. The named number denotes a value of type universal_real
if the type of the static_expression
is a real type.
6
The value denoted by the named number is the value
of the
static_expression, converted
to the corresponding universal type.
{implicit
subtype conversion (named number value) [partial]} Dynamic Semantics
7
{elaboration (number_declaration)
[partial]} The elaboration of a
number_declaration
has no effect.
7.a
Proof: Since the static_expression
was evaluated at compile time.
Examples
8
Examples of number
declarations:
9
Two_Pi :
constant := 2.0*Ada.Numerics.Pi; --
a real number (see A.5)10/2
{
AI-00433-01}
Max :
constant := 500; --
an integer number
Max_Line_Size :
constant := Max/6
; --
the integer 83
Power_16 :
constant := 2**16; --
the integer 65_536
One, Un, Eins :
constant := 1; --
three different names for 1Extensions to Ada 83
10.a
{
extensions to Ada 83}
We
now allow a static expression of any numeric type to initialize a named
number. For integer types, it was possible in Ada 83 to use 'Pos to define
a named number, but there was no way to use a static expression of some
non-universal real type to define a named number. This change is upward
compatible because of the preference rule for the operators of the root
numeric types.
Wording Changes from Ada 83
10.b
We have moved the syntax rule into this subclause.
10.c
AI83-00263 describes the elaboration of a number
declaration in words similar to that of an object_declaration.
However, since there is no expression to be evaluated and no object to
be created, it seems simpler to say that the elaboration has no effect.
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