A.3.2 The Package Characters.Handling
Static Semantics
The library package
Characters.Handling has the following declaration:
--Character classification functions
{
AI05-0185-1}
{
AI12-0004-1}
function Is_Control (Item :
in Character)
return Boolean;
function Is_Graphic (Item :
in Character)
return Boolean;
function Is_Letter (Item :
in Character)
return Boolean;
function Is_Lower (Item :
in Character)
return Boolean;
function Is_Upper (Item :
in Character)
return Boolean;
function Is_Basic (Item :
in Character)
return Boolean;
function Is_Digit (Item :
in Character)
return Boolean;
function Is_Decimal_Digit (Item :
in Character)
return Boolean
renames Is_Digit;
function Is_Hexadecimal_Digit (Item :
in Character)
return Boolean;
function Is_Alphanumeric (Item :
in Character)
return Boolean;
function Is_Special (Item :
in Character)
return Boolean;
function Is_Line_Terminator (Item :
in Character)
return Boolean;
function Is_Mark (Item :
in Character)
return Boolean;
function Is_Other_Format (Item :
in Character)
return Boolean;
function Is_Punctuation_Connector (Item :
in Character)
return Boolean;
function Is_Space (Item :
in Character)
return Boolean;
function Is_NFKC (Item :
in Character)
return Boolean;
--Conversion functions for Character and String
function To_Lower (Item :
in Character)
return Character;
function To_Upper (Item :
in Character)
return Character;
function To_Basic (Item :
in Character)
return Character;
function To_Lower (Item :
in String)
return String;
function To_Upper (Item :
in String)
return String;
function To_Basic (Item :
in String)
return String;
--Classifications of and conversions between Character and ISO 646
subtype ISO_646
is
Character
range Character'Val(0) .. Character'Val(127);
function Is_ISO_646 (Item :
in Character)
return Boolean;
function Is_ISO_646 (Item :
in String)
return Boolean;
function To_ISO_646 (Item :
in Character;
Substitute :
in ISO_646 := ' ')
return ISO_646;
function To_ISO_646 (Item :
in String;
Substitute :
in ISO_646 := ' ')
return String;
{
AI95-00285-01}
{
AI95-00395-01}
--
The functions Is_Character, Is_String, To_Character, To_String, To_Wide_Character,
--
and To_Wide_String are obsolescent; see J.14.Paragraphs 14 through 18 were deleted.
end Ada.Characters.Handling;
Discussion: {
AI95-00395-01}
The
with_clause
for Ada.Characters.Conversions is needed for the definition of the obsolescent
functions (see
J.14). It would be odd to put
this clause into
J.14 as it was not present
in Ada 95, and
with_clauses
are semantically neutral to clients anyway.
In the description below for each function that returns
a Boolean result, the effect is described in terms of the conditions
under which the value True is returned. If these conditions are not met,
then the function returns False.
Each of the following classification functions has
a formal Character parameter, Item, and returns a Boolean result.
True if Item is a control character. A control character is a
character whose position is in one of the ranges 0..31 or 127..159.
True if Item is a graphic character. A graphic character is a
character whose position is in one of the ranges 32..126 or 160..255.
True if Item is a letter. A letter is a character that is in one
of the ranges 'A'..'Z' or 'a'..'z', or whose position is in one of the
ranges 192..214, 216..246, or 248..255.
True if Item is a lower-case letter. A lower-case letter is a
character that is in the range 'a'..'z', or whose position is in one
of the ranges 223..246 or 248..255.
True if Item is an upper-case letter. An upper-case letter is
a character that is in the range 'A'..'Z' or whose position is in one
of the ranges 192..214 or 216.. 222.
True if Item is a basic letter. A basic letter is a character
that is in one of the ranges 'A'..'Z' and 'a'..'z', or that is one of
the following: 'Æ', 'æ', 'Ð', 'ð', 'Þ', 'þ',
or 'ß'.
True if Item is a decimal digit. A decimal digit is a character
in the range '0'..'9'.
Is_Decimal_Digit
A renaming of Is_Digit.
True if Item is a hexadecimal digit. A hexadecimal digit is a
character that is either a decimal digit or that is in one of the ranges
'A' .. 'F' or 'a' .. 'f'.
True if Item is an alphanumeric character. An alphanumeric character
is a character that is either a letter or a decimal digit.
True if Item is a special graphic character. A special graphic character
is a graphic character that is not alphanumeric.
True if Item is a character with position 10 .. 13 (Line_Feed, Line_Tabulation,
Form_Feed, Carriage_Return) or 133 (Next_Line).
Never True (no value of type Character has categories Mark, Non-Spacing
or Mark, Spacing Combining).
True if Item is a character with position 173 (Soft_Hyphen).
True if Item is a character with position 95 ('_', known as Low_Line
or Underscore).
True if Item is a character with position 32 (' ') or 160 (No_Break_Space).
True if Item can be present in a string normalized to Normalization Form
KC (as defined by Clause 22 of ISO/IEC 10646:2020); this includes all
characters except those with positions 160, 168, 170, 175, 178, 179,
180, 181, 184, 185, 186, 188, 189, and 190.
Each of the names To_Lower, To_Upper, and To_Basic
refers to two functions: one that converts from Character to Character,
and the other that converts from String to String. The result of each
Character-to-Character function is described below, in terms of the conversion
applied to Item, its formal Character parameter. The result of each String-to-String
conversion is obtained by applying to each element of the function's
String parameter the corresponding Character-to-Character conversion;
the result is the null String if the value of the formal parameter is
the null String. The lower bound of the result String is 1.
To_Lower
Returns the corresponding lower-case value for Item if Is_Upper(Item),
and returns Item otherwise.
To_Upper
Returns the corresponding upper-case value for Item if Is_Lower(Item)
and Item has an upper-case form, and returns Item otherwise. The lower
case letters 'ß' and 'ÿ' do not have upper case forms.
To_Basic
Returns the letter corresponding to Item but with no diacritical mark,
if Item is a letter but not a basic letter; returns Item otherwise.
The following set of functions test for membership
in the ISO 646 character range, or convert between ISO 646 and Character.
Is_ISO_646
The function whose formal parameter, Item, is of type Character returns
True if Item is in the subtype ISO_646.
Is_ISO_646
The function whose formal parameter, Item, is of type String returns
True if Is_ISO_646(Item(I)) is True for each I in Item'Range.
To_ISO_646
The function whose first formal parameter, Item, is of type Character
returns Item if Is_ISO_646(Item), and returns the Substitute ISO_646
character otherwise.
To_ISO_646
The function whose first formal parameter, Item, is of type String returns
the String whose Range is 1..Item'Length and each of whose elements is
given by To_ISO_646 of the corresponding element in Item.
Paragraphs
42 through 49 were deleted.
NOTE 1 A basic letter is a letter
without a diacritical mark.
NOTE 2 Except
for the hexadecimal digits, basic letters, and ISO_646 characters, the
categories identified in the classification functions form a strict hierarchy:
— Control characters
— Graphic characters
— Alphanumeric characters
— Letters
— Upper-case letters
— Lower-case letters
— Decimal digits
— Special graphic characters
Ramification: Thus each Character value
is either a control character or a graphic character but not both; each
graphic character is either an alphanumeric or special graphic but not
both; each alphanumeric is either a letter or decimal digit but not both;
each letter is either upper case or lower case but not both.
NOTE 3 {
AI05-0114-1}
There are certain characters which are defined to be lower case letters
by ISO 10646 and are therefore allowed in identifiers, but are not considered
lower case letters by Ada.Characters.Handling.
Reason: This is to maintain runtime compatibility
with the Ada 95 definitions of these functions. We don't list the exact
characters involved because they're likely to change in future character
set standards; the list for ISO 10646:2011 can be found in
AI05-0114-1.
Ramification: No version of Characters.Handling
is intended to do portable (Ada-version independent) manipulation of
Ada identifiers. The classification given by Wide_Characters.Handling
will be correct for the current implementation for Ada 2012 identifiers,
but it might not be correct for a different implementation or version
of Ada.
Extensions to Ada 95
{
AI95-00362-01}
Characters.Handling is now Pure, so it can be used
in pure units.
Incompatibilities With Ada 2005
{
AI05-0185-1}
Added additional classification routines so that
Characters.Handling has all of the routines available in Wide_Characters.Handling.
If Characters.Handling is referenced in a
use_clause,
and an entity
E with a
defining_identifier
that is the same as one of the new functions is defined in a package
that is also referenced in a
use_clause,
the entity
E may no longer be use-visible, resulting in errors.
This should be rare and is easily fixed if it does occur.
Wording Changes from Ada 95
{
AI95-00285-01}
{
AI05-0248-1}
We no longer talk about localized character sets; these are a nonstandard
mode, which is none of our business.
Wording Changes from Ada 2005
{
AI05-0114-1}
Correction: Added a note to clarify that these functions don't
have any relationship to the characters allowed in identifiers.
Incompatibilities With Ada 2012
{
AI12-0004-1}
Added an additional classification routine Is_NFKC.
Therefore, a use clause conflict is possible; see the introduction of
Annex A for more on this topic.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
