1/*
2 *******************************************************************************
3 * Copyright (C) 1996-2005, International Business Machines Corporation and    *
4 * others. All Rights Reserved.                                                *
5 *******************************************************************************
6 */
7package com.ibm.icu.text;
8import java.text.ParsePosition;
9
10/**
11 * An interface that defines both lookup protocol and parsing of
12 * symbolic names.
13 *
14 * <p>This interface is used by UnicodeSet to resolve $Variable style
15 * references that appear in set patterns.  RBBI and Transliteration
16 * both independently implement this interface.
17 *
18 * <p>A symbol table maintains two kinds of mappings.  The first is
19 * between symbolic names and their values.  For example, if the
20 * variable with the name "start" is set to the value "alpha"
21 * (perhaps, though not necessarily, through an expression such as
22 * "$start=alpha"), then the call lookup("start") will return the
23 * char[] array ['a', 'l', 'p', 'h', 'a'].
24 *
25 * <p>The second kind of mapping is between character values and
26 * UnicodeMatcher objects.  This is used by RuleBasedTransliterator,
27 * which uses characters in the private use area to represent objects
28 * such as UnicodeSets.  If U+E015 is mapped to the UnicodeSet [a-z],
29 * then lookupMatcher(0xE015) will return the UnicodeSet [a-z].
30 *
31 * <p>Finally, a symbol table defines parsing behavior for symbolic
32 * names.  All symbolic names start with the SYMBOL_REF character.
33 * When a parser encounters this character, it calls parseReference()
34 * with the position immediately following the SYMBOL_REF.  The symbol
35 * table parses the name, if there is one, and returns it.
36 *
37 * @stable ICU 2.8
38 */
39public interface SymbolTable {
40
41    /**
42     * The character preceding a symbol reference name.
43     * @stable ICU 2.8
44     */
45    static final char SYMBOL_REF = '$';
46
47    /**
48     * Lookup the characters associated with this string and return it.
49     * Return <tt>null</tt> if no such name exists.  The resultant
50     * array may have length zero.
51     * @param s the symbolic name to lookup
52     * @return a char array containing the name's value, or null if
53     * there is no mapping for s.
54     * @stable ICU 2.8
55     */
56    char[] lookup(String s);
57
58    /**
59     * Lookup the UnicodeMatcher associated with the given character, and
60     * return it.  Return <tt>null</tt> if not found.
61     * @param ch a 32-bit code point from 0 to 0x10FFFF inclusive.
62     * @return the UnicodeMatcher object represented by the given
63     * character, or null if there is no mapping for ch.
64     * @stable ICU 2.8
65     */
66    UnicodeMatcher lookupMatcher(int ch);
67
68    /**
69     * Parse a symbol reference name from the given string, starting
70     * at the given position.  If no valid symbol reference name is
71     * found, return null and leave pos unchanged.  That is, if the
72     * character at pos cannot start a name, or if pos is at or after
73     * text.length(), then return null.  This indicates an isolated
74     * SYMBOL_REF character.
75     * @param text the text to parse for the name
76     * @param pos on entry, the index of the first character to parse.
77     * This is the character following the SYMBOL_REF character.  On
78     * exit, the index after the last parsed character.  If the parse
79     * failed, pos is unchanged on exit.
80     * @param limit the index after the last character to be parsed.
81     * @return the parsed name, or null if there is no valid symbolic
82     * name at the given position.
83     * @stable ICU 2.8
84     */
85    String parseReference(String text, ParsePosition pos, int limit);
86}
87