# charset.h | documentation

    #charset "us-ascii"
    #pragma once

    /*
     *   Copyright (c) 2001, 2006 Michael J. Roberts
     *
     *   This file is part of TADS 3.
     *
     *   This header defines the CharacterSet intrinsic class.
     */

    /* include our base class definition */
    #include "systype.h"

    /*
     *   The CharacterSet intrinsic class provides information on character set
     *   translations and can be used to translate between the Unicode character
     *   set that the T3 VM uses internally for string values and the local
     *   character set or sets used for display, keyboard input, and file I/O.
     */
    intrinsic class CharacterSet 'character-set/030001': Object
    {
        /*
         *   Constructor:
         *
         *   new CharacterSet(charsetName) - creates an object to represent the
         *   named local character set.  Certain common character set names are
         *   built into the system:
         *
         *   us-ascii - the plain 7-bit ASCII character set
         *.  latin1 - 8-bit Western Europe extended ASCII (also called ISO 8859-1)
         *.  utf-8 - Unicode UTF-8 (varying byte length Unicode encoding)
         *.  utf-16le - little-endian 16-bit Unicode
         *.  utf-16be - big-endian 16-bit Unicode
         *
         *   You can extend this basic set using mapping files.  You can create
         *   your own mapping files (see the System Manual to learn how), so
         *   there's essentially no limit to the character sets that TADS can
         *   work with.  You'll probably never need to create your own custom
         *   mappings, though, because the standard TADS distributions include a
         *   large set of pre-built mappings that cover most systems currently in
         *   use.  The standard set includes the various ISO 8859 variants, plus
         *   proprietary code pages for Windows, DOS, and Mac OS.
         *
         *   If the named mapping doesn't exist, a CharacterSet object will still
         *   be created, but it'll throw an error (UnknownCharacterSetException)
         *   if you attempt to use it to perform any mappings.  You can determine
         *   if the mapping exists with the isMappingKnown method.
         */

        /*
         *   Get the name of the character set.  This simply returns the name
         *   that was given to construct the character set.
         */
        getName();

        /*
         *   Determine if the mapping is known.  This returns true if the
         *   character set has a known local mapping, nil if not.  Note that it
         *   doesn't matter whether or not the character set is actually in use
         *   on the local platform; all that matters is that a T3 mapping file
         *   is available on this machine.
         */
        isMappingKnown();

        /*
         *   Determine if a character or string of characters is mappable to this
         *   character set.  If the input is an integer, it represents the
         *   Unicode character code for a single character; if the input is a
         *   string, each character in the string is checked.  This returns true
         *   if every character given has a valid mapping in the local character
         *   set, nil if not.  Note that if a string is given, and even one
         *   character is not mappable, this returns nil.
         */
        isMappable(val);

        /*
         *   Determine if a character or string of characters is "round-trip"
         *   mappable to this character set.  If the input is an integer, it
         *   represents a Unicode character code to be tested; if the input is a
         *   string, each character in the string is tested.  Returns true if
         *   every character given has a valid round-trip mapping, nil if not.
         *
         *   A character has a round-trip mapping if it can be mapped to this
         *   local character set and then back to Unicode to yield the original
         *   character.  If a character has a round-trip mapping, then in general
         *   the character has an exact representation in the local character set
         *   (as opposed to an approximation: if 'a-umlaut' maps to a simple
         *   unaccented 'a', or to 'ae', then it has only an approximated
         *   representation).
         */
        isRoundTripMappable(val);
    }

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