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A
*range* has a *lower bound* and an *upper bound* and specifies
a subset of the values of some scalar type (the *type of the range*).
A range with lower bound L and upper bound R is described by “L
.. R”. If R is less than L, then the range
is a *null range*, and specifies an empty set of values. Otherwise,
the range specifies the values of the type from the lower bound to the
upper bound, inclusive. A value *belongs* to
a range if it is of the type of the range, and is in the subset of values
specified by the range. A value *satisfies*
a range constraint if it belongs to the associated range. One
range is *included* in another if all values that belong to the
first range also belong to the second.

For a subtype_indication
containing a range_constraint,
either directly or as part of some other scalar_constraint,
the type of the range
shall resolve to that of the type determined by the subtype_mark
of the subtype_indication.
For a range
of a given type, the simple_expressions
of the range
(likewise, the simple_expressions
of the equivalent range
for a range_attribute_reference)
are expected to be of the type of the range.

The *base range* of a scalar
type is the range of finite values of the type that can be represented
in every unconstrained object of the type; it is also the range supported
at a minimum for intermediate values during the evaluation of expressions
involving predefined operators of the type.

A constrained
scalar subtype is one to which a range constraint applies. The
*range* of a constrained scalar subtype is the range associated
with the range constraint of the subtype. The *range* of an unconstrained
scalar subtype is the base range of its type.

A range is *compatible*
with a scalar subtype if and only if it is either a null range or each
bound of the range belongs to the range of the subtype. A
range_constraint
is *compatible* with a scalar subtype if and only if its range is
compatible with the subtype.

The elaboration of a range_constraint
consists of the evaluation of the range.
The evaluation of a range
determines a lower bound and an upper bound. If simple_expressions
are given to specify bounds, the evaluation of the range
evaluates these simple_expressions
in an arbitrary order, and converts them to the type of the range.
If a range_attribute_reference
is given, the evaluation of the range
consists of the evaluation of the range_attribute_reference.

For every scalar subtype
S, the following attributes are defined:

S'First

S'Last

S'Range

S'Base

S'Base denotes an unconstrained
subtype of the type of S. This unconstrained subtype is called the *base
subtype* of the type.

S'Min

The function returns the lesser of the
values of the two parameters.

S'Max

The function returns the greater of the
values of the two parameters.

S'Succ

For an enumeration
type, the function returns the value whose position number is one more
than that of the value of *Arg*; Constraint_Error
is raised if there is no such value of the type. For an integer type,
the function returns the result of adding one to the value of *Arg*.
For a fixed point type, the function returns the result of adding *small*
to the value of *Arg*. For a floating
point type, the function returns the machine number (as defined in 3.5.7)
immediately above the value of *Arg*;
Constraint_Error is raised if
there is no such machine number.

S'Pred

For an enumeration
type, the function returns the value whose position number is one less
than that of the value of *Arg*; Constraint_Error
is raised if there is no such value of the type. For an integer type,
the function returns the result of subtracting one from the value of
*Arg*. For a fixed point type, the function
returns the result of subtracting *small* from the value of *Arg*.
For a floating point type, the function returns the machine number (as
defined in 3.5.7) immediately below the value
of *Arg*; Constraint_Error
is raised if there is no such machine number.

S'Wide_Wide_Width

S'Wide_Wide_Width denotes the maximum length of a Wide_Wide_String returned by S'Wide_Wide_Image over all values of the subtype S, assuming a default implementation of S'Put_Image. It denotes zero for a subtype that has a null range. Its type is

S'Wide_Width

S'Wide_Width denotes the maximum
length of a Wide_String returned by S'Wide_Image over all values of the
subtype S, assuming a default implementation of S'Put_Image. It denotes
zero for a subtype that has a null range. Its type is *universal_integer*.

S'Width

S'Width denotes the maximum length
of a String returned by S'Image over all values of the subtype S, assuming
a default implementation of S'Put_Image. It denotes zero for a subtype
that has a null range. Its type is *universal_integer*.

S'Wide_Wide_Value

This function returns a value given an
image of the value as a Wide_Wide_String, ignoring any leading or trailing
spaces.

For
the evaluation of a call on S'Wide_Wide_Value for an enumeration subtype
S, if the sequence of characters of the parameter (ignoring leading and
trailing spaces) has the syntax of an enumeration literal and if it corresponds
to a literal of the type of S (or corresponds to the result of S'Wide_Wide_Image
for a nongraphic character of the type), the result is the corresponding
enumeration value; otherwise,
Constraint_Error is raised.

For the evaluation
of a call on S'Wide_Wide_Value for an integer subtype S, if the sequence
of characters of the parameter (ignoring leading and trailing spaces)
has the syntax of an integer literal, with an optional leading sign character
(plus or minus for a signed type; only plus for a modular type), and
the corresponding numeric value belongs to the base range of the type
of S, then that value is the result; otherwise,
Constraint_Error is raised.

For the evaluation
of a call on S'Wide_Wide_Value for a real subtype S, if the sequence
of characters of the parameter (ignoring leading and trailing spaces)
has the syntax of one of the following:

with an optional leading
sign character (plus or minus), and if the corresponding numeric value
belongs to the base range of the type of S, then that value is the result;
otherwise, Constraint_Error is
raised. The sign of a zero value is preserved (positive if none has been
specified) if S'Signed_Zeros is True.

S'Wide_Value

This function returns a value given an
image of the value as a Wide_String, ignoring any leading or trailing
spaces.

For
the evaluation of a call on S'Wide_Value for an enumeration subtype S,
if the sequence of characters of the parameter (ignoring leading and
trailing spaces) has the syntax of an enumeration literal and if it corresponds
to a literal of the type of S (or corresponds to the result of S'Wide_Image
for a value of the type, assuming a default implementation of S'Put_Image),
the result is the corresponding enumeration value; otherwise,
Constraint_Error is raised. For a numeric subtype S, the evaluation of
a call on S'Wide_Value with *Arg* of
type Wide_String is equivalent to a call on S'Wide_Wide_Value for a corresponding
*Arg* of type Wide_Wide_String.

S'Value

This function returns a value given an
image of the value as a String, ignoring any leading or trailing spaces.

For
the evaluation of a call on S'Value for an enumeration subtype S, if
the sequence of characters of the parameter (ignoring leading and trailing
spaces) has the syntax of an enumeration literal and if it corresponds
to a literal of the type of S (or corresponds to the result of S'Image
for a value of the type, assuming a default implementation of S'Put_Image),
the result is the corresponding enumeration value; otherwise,
Constraint_Error is raised. For a numeric subtype S, the evaluation of
a call on S'Value with *Arg* of type
String is equivalent to a call on S'Wide_Wide_Value for a corresponding
*Arg* of type Wide_Wide_String.

An implementation may extend the Wide_Wide_Value,
Wide_Value, Value, Wide_Wide_Image, Wide_Image, and Image attributes
of a floating point type to support special values such as infinities
and NaNs.

An implementation may extend the Wide_Wide_Value,
Wide_Value, and Value attributes of a character type to accept strings
of the form “Hex_*hhhhhhhh*” (ignoring case) for any
character (not just the ones for which Wide_Wide_Image would produce
that form — see 3.5.2), as well as
three-character strings of the form “'*X*'”, where *X*
is any character, including nongraphic characters.

For a scalar type,
the following language-defined representation aspect may be specified
with an aspect_specification
(see 13.1.1):

Default_Value

This aspect shall be specified by a static expression, and that expression shall be explicit, even if the aspect has a boolean type. Default_Value shall be specified only on a full_type_declaration.

If a derived type inherits a boolean Default_Value
aspect, the aspect may be specified to have any value for the derived
type. If a derived type *T* does not inherit a Default_Value aspect,
it shall not specify such an aspect if it inherits a primitive subprogram
that has a parameter of type *T* of mode **out**.

The expected type for the expression
specified for the Default_Value aspect is the type defined by the full_type_declaration
on which it appears.

NOTE 1 The evaluation of S'First
or S'Last never raises an exception. If a scalar subtype S has a nonnull
range, S'First and S'Last belong to this range. These values can, for
example, always be assigned to a variable of subtype S.

NOTE 2 For a subtype of a scalar
type, the result delivered by the attributes Succ, Pred, and Value can
be outside to the subtype; similarly, the actual parameters of the attributes
Succ, Pred, and Image can also be outside the subtype.

NOTE 3 For any value V (including
any nongraphic character) of an enumeration subtype S without a specified
Put_Image (see 4.10), S'Value(S'Image(V))
equals V, as do S'Wide_Value(S'Wide_Image(V)) and S'Wide_Wide_Value(S'Wide_Wide_Image(V)).
None of these expressions ever raise Constraint_Error.

-10 .. 10

X .. X + 1

0.0 .. 2.0*Pi

Red .. Green --* see 3.5.1*

1 .. 0 --* a null range*

Table'Range --* a range attribute reference (see 3.6)*

X .. X + 1

0.0 .. 2.0*Pi

Red .. Green --

1 .. 0 --

Table'Range --

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