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 // © 2016 and later: Unicode, Inc. and others.
 // License & terms of use: http://www.unicode.org/copyright.html
 /*
 *******************************************************************************
 * Copyright (C) 1997-2015, International Business Machines Corporation and others.
 * All Rights Reserved.
 *******************************************************************************
 */
 
 #ifndef RBNF_H
 #define RBNF_H
 
 #include "unicode/utypes.h"
 
 #if U_SHOW_CPLUSPLUS_API
 
 /**
  * \file
  * \brief C++ API: Rule Based Number Format
  */
 
 /**
  * \def U_HAVE_RBNF
  * This will be 0 if RBNF support is not included in ICU
  * and 1 if it is.
  *
  * @stable ICU 2.4
  */
 #if UCONFIG_NO_FORMATTING
 #define U_HAVE_RBNF 0
 #else
 #define U_HAVE_RBNF 1
 
 #include "unicode/dcfmtsym.h"
 #include "unicode/fmtable.h"
 #include "unicode/locid.h"
 #include "unicode/numfmt.h"
 #include "unicode/unistr.h"
 #include "unicode/strenum.h"
 #include "unicode/brkiter.h"
 #include "unicode/upluralrules.h"
 
 U_NAMESPACE_BEGIN
 
 class NFRule;
 class NFRuleSet;
 class LocalizationInfo;
 class PluralFormat;
 class RuleBasedCollator;
 
 /**
  * Tags for the predefined rulesets.
  *
  * @stable ICU 2.2
  */
 enum URBNFRuleSetTag {
     /**
      * Requests predefined ruleset for spelling out numeric values in words.
      * @stable ICU 2.2
      */
     URBNF_SPELLOUT,
     /**
      * Requests predefined ruleset for the ordinal form of a number.
      * @stable ICU 2.2
      */
     URBNF_ORDINAL,
 #ifndef U_HIDE_DEPRECATED_API
     /**
      * Requests predefined ruleset for formatting a value as a duration in hours, minutes, and seconds.
      * @deprecated ICU 74 Use MeasureFormat instead.
      */
     URBNF_DURATION,
 #endif // U_HIDE_DERECATED_API
     /**
      * Requests predefined ruleset for various non-place-value numbering systems.
      * WARNING: The same resource contains rule sets for a variety of different numbering systems.
      * You need to call setDefaultRuleSet() on the formatter to choose the actual numbering system.
      * @stable ICU 2.2
      */
     URBNF_NUMBERING_SYSTEM = 3,
 #ifndef U_HIDE_DEPRECATED_API
     /**
      * One more than the highest normal URBNFRuleSetTag value.
      * @deprecated ICU 58 The numeric value may change over time, see ICU ticket #12420.
      */
     URBNF_COUNT
 #endif  // U_HIDE_DEPRECATED_API
 };
 
 /**
  * The RuleBasedNumberFormat class formats numbers according to a set of rules. This number formatter is
  * typically used for spelling out numeric values in words (e.g., 25,3476 as
  * "twenty-five thousand three hundred seventy-six" or "vingt-cinq mille trois
  * cents soixante-seize" or
  * "fünfundzwanzigtausenddreihundertsechsundsiebzig"), but can also be used for
  * other complicated formatting tasks, such as formatting a number of seconds as hours,
  * minutes and seconds (e.g., 3,730 as "1:02:10").
  *
  * <p>The resources contain three predefined formatters for each locale: spellout, which
  * spells out a value in words (123 is &quot;one hundred twenty-three&quot;); ordinal, which
  * appends an ordinal suffix to the end of a numeral (123 is &quot;123rd&quot;); and
  * duration, which shows a duration in seconds as hours, minutes, and seconds (123 is
  * &quot;2:03&quot;).&nbsp; The client can also define more specialized <tt>RuleBasedNumberFormat</tt>s
  * by supplying programmer-defined rule sets.</p>
  *
  * <p>The behavior of a <tt>RuleBasedNumberFormat</tt> is specified by a textual description
  * that is either passed to the constructor as a <tt>String</tt> or loaded from a resource
  * bundle. In its simplest form, the description consists of a semicolon-delimited list of <em>rules.</em>
  * Each rule has a string of output text and a value or range of values it is applicable to.
  * In a typical spellout rule set, the first twenty rules are the words for the numbers from
  * 0 to 19:</p>
  *
  * <pre>zero; one; two; three; four; five; six; seven; eight; nine;
  * ten; eleven; twelve; thirteen; fourteen; fifteen; sixteen; seventeen; eighteen; nineteen;</pre>
  *
  * <p>For larger numbers, we can use the preceding set of rules to format the ones place, and
  * we only have to supply the words for the multiples of 10:</p>
  *
  * <pre> 20: twenty[-&gt;&gt;];
  * 30: thirty[-&gt;&gt;];
  * 40: forty[-&gt;&gt;];
  * 50: fifty[-&gt;&gt;];
  * 60: sixty[-&gt;&gt;];
  * 70: seventy[-&gt;&gt;];
  * 80: eighty[-&gt;&gt;];
  * 90: ninety[-&gt;&gt;];</pre>
  *
  * <p>In these rules, the <em>base value</em> is spelled out explicitly and set off from the
  * rule's output text with a colon. The rules are in a sorted list, and a rule is applicable
  * to all numbers from its own base value to one less than the next rule's base value. The
  * &quot;&gt;&gt;&quot; token is called a <em>substitution</em> and tells the formatter to
  * isolate the number's ones digit, format it using this same set of rules, and place the
  * result at the position of the &quot;&gt;&gt;&quot; token. Text in brackets is omitted if
  * the number being formatted is an even multiple of 10 (the hyphen is a literal hyphen; 24
  * is &quot;twenty-four,&quot; not &quot;twenty four&quot;).</p>
  *
  * <p>For even larger numbers, we can actually look up several parts of the number in the
  * list:</p>
  *
  * <pre>100: &lt;&lt; hundred[ &gt;&gt;];</pre>
  *
  * <p>The &quot;&lt;&lt;&quot; represents a new kind of substitution. The &lt;&lt; isolates
  * the hundreds digit (and any digits to its left), formats it using this same rule set, and
  * places the result where the &quot;&lt;&lt;&quot; was. Notice also that the meaning of
  * &gt;&gt; has changed: it now refers to both the tens and the ones digits. The meaning of
  * both substitutions depends on the rule's base value. The base value determines the rule's <em>divisor,</em>
  * which is the highest power of 10 that is less than or equal to the base value (the user
  * can change this). To fill in the substitutions, the formatter divides the number being
  * formatted by the divisor. The integral quotient is used to fill in the &lt;&lt;
  * substitution, and the remainder is used to fill in the &gt;&gt; substitution. The meaning
  * of the brackets changes similarly: text in brackets is omitted if the value being
  * formatted is an even multiple of the rule's divisor. The rules are applied recursively, so
  * if a substitution is filled in with text that includes another substitution, that
  * substitution is also filled in.</p>
  *
  * <p>This rule covers values up to 999, at which point we add another rule:</p>
  *
  * <pre>1000: &lt;&lt; thousand[ &gt;&gt;];</pre>
  *
  * <p>Again, the meanings of the brackets and substitution tokens shift because the rule's
  * base value is a higher power of 10, changing the rule's divisor. This rule can actually be
  * used all the way up to 999,999. This allows us to finish out the rules as follows:</p>
  *
  * <pre> 1,000,000: &lt;&lt; million[ &gt;&gt;];
  * 1,000,000,000: &lt;&lt; billion[ &gt;&gt;];
  * 1,000,000,000,000: &lt;&lt; trillion[ &gt;&gt;];
  * 1,000,000,000,000,000: OUT OF RANGE!;</pre>
  *
  * <p>Commas, periods, and spaces can be used in the base values to improve legibility and
  * are ignored by the rule parser. The last rule in the list is customarily treated as an
  * &quot;overflow rule,&quot; applying to everything from its base value on up, and often (as
  * in this example) being used to print out an error message or default representation.
  * Notice also that the size of the major groupings in large numbers is controlled by the
  * spacing of the rules: because in English we group numbers by thousand, the higher rules
  * are separated from each other by a factor of 1,000.</p>
  *
  * <p>To see how these rules actually work in practice, consider the following example:
  * Formatting 25,430 with this rule set would work like this:</p>
  *
  * <table border="0" width="100%">
  *   <tr>
  *     <td><strong>&lt;&lt; thousand &gt;&gt;</strong></td>
  *     <td>[the rule whose base value is 1,000 is applicable to 25,340]</td>
  *   </tr>
  *   <tr>
  *     <td><strong>twenty-&gt;&gt;</strong> thousand &gt;&gt;</td>
  *     <td>[25,340 over 1,000 is 25. The rule for 20 applies.]</td>
  *   </tr>
  *   <tr>
  *     <td>twenty-<strong>five</strong> thousand &gt;&gt;</td>
  *     <td>[25 mod 10 is 5. The rule for 5 is &quot;five.&quot;</td>
  *   </tr>
  *   <tr>
  *     <td>twenty-five thousand <strong>&lt;&lt; hundred &gt;&gt;</strong></td>
  *     <td>[25,340 mod 1,000 is 340. The rule for 100 applies.]</td>
  *   </tr>
  *   <tr>
  *     <td>twenty-five thousand <strong>three</strong> hundred &gt;&gt;</td>
  *     <td>[340 over 100 is 3. The rule for 3 is &quot;three.&quot;]</td>
  *   </tr>
  *   <tr>
  *     <td>twenty-five thousand three hundred <strong>forty</strong></td>
  *     <td>[340 mod 100 is 40. The rule for 40 applies. Since 40 divides
  *     evenly by 10, the hyphen and substitution in the brackets are omitted.]</td>
  *   </tr>
  * </table>
  *
  * <p>The above syntax suffices only to format positive integers. To format negative numbers,
  * we add a special rule:</p>
  *
  * <pre>-x: minus &gt;&gt;;</pre>
  *
  * <p>This is called a <em>negative-number rule,</em> and is identified by &quot;-x&quot;
  * where the base value would be. This rule is used to format all negative numbers. the
  * &gt;&gt; token here means &quot;find the number's absolute value, format it with these
  * rules, and put the result here.&quot;</p>
  *
  * <p>We also add a special rule called a <em>fraction rule </em>for numbers with fractional
  * parts:</p>
  *
  * <pre>x.x: &lt;&lt; point &gt;&gt;;</pre>
  *
  * <p>This rule is used for all positive non-integers (negative non-integers pass through the
  * negative-number rule first and then through this rule). Here, the &lt;&lt; token refers to
  * the number's integral part, and the &gt;&gt; to the number's fractional part. The
  * fractional part is formatted as a series of single-digit numbers (e.g., 123.456 would be
  * formatted as &quot;one hundred twenty-three point four five six&quot;).</p>
  *
  * <p>To see how this rule syntax is applied to various languages, examine the resource data.</p>
  *
  * <p>There is actually much more flexibility built into the rule language than the
  * description above shows. A formatter may own multiple rule sets, which can be selected by
  * the caller, and which can use each other to fill in their substitutions. Substitutions can
  * also be filled in with digits, using a DecimalFormat object. There is syntax that can be
  * used to alter a rule's divisor in various ways. And there is provision for much more
  * flexible fraction handling. A complete description of the rule syntax follows:</p>
  *
  * <hr>
  *
  * <p>The description of a <tt>RuleBasedNumberFormat</tt>'s behavior consists of one or more <em>rule
  * sets.</em> Each rule set consists of a name, a colon, and a list of <em>rules.</em> A rule
  * set name must begin with a % sign. Rule sets with names that begin with a single % sign
  * are <em>public:</em> the caller can specify that they be used to format and parse numbers.
  * Rule sets with names that begin with %% are <em>private:</em> they exist only for the use
  * of other rule sets. If a formatter only has one rule set, the name may be omitted.</p>
  *
  * <p>The user can also specify a special &quot;rule set&quot; named <tt>%%lenient-parse</tt>.
  * The body of <tt>%%lenient-parse</tt> isn't a set of number-formatting rules, but a <tt>RuleBasedCollator</tt>
  * description which is used to define equivalences for lenient parsing. For more information
  * on the syntax, see <tt>RuleBasedCollator</tt>. For more information on lenient parsing,
  * see <tt>setLenientParse()</tt>.  <em>Note:</em> symbols that have syntactic meaning
  * in collation rules, such as '&amp;', have no particular meaning when appearing outside
  * of the <tt>lenient-parse</tt> rule set.</p>
  *
  * <p>The body of a rule set consists of an ordered, semicolon-delimited list of <em>rules.</em>
  * Internally, every rule has a base value, a divisor, rule text, and zero, one, or two <em>substitutions.</em>
  * These parameters are controlled by the description syntax, which consists of a <em>rule
  * descriptor,</em> a colon, and a <em>rule body.</em></p>
  *
  * <p>A rule descriptor can take one of the following forms (text in <em>italics</em> is the
  * name of a token):</p>
  *
  * <table border="0" width="100%">
  *   <tr>
  *     <td><em>bv</em>:</td>
  *     <td><em>bv</em> specifies the rule's base value. <em>bv</em> is a decimal
  *     number expressed using ASCII digits. <em>bv</em> may contain spaces, period, and commas,
  *     which are ignored. The rule's divisor is the highest power of 10 less than or equal to
  *     the base value.</td>
  *   </tr>
  *   <tr>
  *     <td><em>bv</em>/<em>rad</em>:</td>
  *     <td><em>bv</em> specifies the rule's base value. The rule's divisor is the
  *     highest power of <em>rad</em> less than or equal to the base value.</td>
  *   </tr>
  *   <tr>
  *     <td><em>bv</em>&gt;:</td>
  *     <td><em>bv</em> specifies the rule's base value. To calculate the divisor,
  *     let the radix be 10, and the exponent be the highest exponent of the radix that yields a
  *     result less than or equal to the base value. Every &gt; character after the base value
  *     decreases the exponent by 1. If the exponent is positive or 0, the divisor is the radix
  *     raised to the power of the exponent; otherwise, the divisor is 1.</td>
  *   </tr>
  *   <tr>
  *     <td><em>bv</em>/<em>rad</em>&gt;:</td>
  *     <td><em>bv</em> specifies the rule's base value. To calculate the divisor,
  *     let the radix be <em>rad</em>, and the exponent be the highest exponent of the radix that
  *     yields a result less than or equal to the base value. Every &gt; character after the radix
  *     decreases the exponent by 1. If the exponent is positive or 0, the divisor is the radix
  *     raised to the power of the exponent; otherwise, the divisor is 1.</td>
  *   </tr>
  *   <tr>
  *     <td>-x:</td>
  *     <td>The rule is a negative-number rule.</td>
  *   </tr>
  *   <tr>
  *     <td>x.x:</td>
  *     <td>The rule is an <em>improper fraction rule</em>. If the full stop in
  *     the middle of the rule name is replaced with the decimal point
  *     that is used in the language or DecimalFormatSymbols, then that rule will
  *     have precedence when formatting and parsing this rule. For example, some
  *     languages use the comma, and can thus be written as x,x instead. For example,
  *     you can use "x.x: &lt;&lt; point &gt;&gt;;x,x: &lt;&lt; comma &gt;&gt;;" to
  *     handle the decimal point that matches the language's natural spelling of
  *     the punctuation of either the full stop or comma.</td>
  *   </tr>
  *   <tr>
  *     <td>0.x:</td>
  *     <td>The rule is a <em>proper fraction rule</em>. If the full stop in
  *     the middle of the rule name is replaced with the decimal point
  *     that is used in the language or DecimalFormatSymbols, then that rule will
  *     have precedence when formatting and parsing this rule. For example, some
  *     languages use the comma, and can thus be written as 0,x instead. For example,
  *     you can use "0.x: point &gt;&gt;;0,x: comma &gt;&gt;;" to
  *     handle the decimal point that matches the language's natural spelling of
  *     the punctuation of either the full stop or comma.</td>
  *   </tr>
  *   <tr>
  *     <td>x.0:</td>
  *     <td>The rule is a <em>default rule</em>. If the full stop in
  *     the middle of the rule name is replaced with the decimal point
  *     that is used in the language or DecimalFormatSymbols, then that rule will
  *     have precedence when formatting and parsing this rule. For example, some
  *     languages use the comma, and can thus be written as x,0 instead. For example,
  *     you can use "x.0: &lt;&lt; point;x,0: &lt;&lt; comma;" to
  *     handle the decimal point that matches the language's natural spelling of
  *     the punctuation of either the full stop or comma.</td>
  *   </tr>
  *   <tr>
  *     <td>Inf:</td>
  *     <td>The rule for infinity.</td>
  *   </tr>
  *   <tr>
  *     <td>NaN:</td>
  *     <td>The rule for an IEEE 754 NaN (not a number).</td>
  *   </tr>
  *   <tr>
  *     <td><em>nothing</em></td>
  *     <td>If the rule's rule descriptor is left out, the base value is one plus the
  *     preceding rule's base value (or zero if this is the first rule in the list) in a normal
  *     rule set.&nbsp; In a fraction rule set, the base value is the same as the preceding rule's
  *     base value.</td>
  *   </tr>
  * </table>
  *
  * <p>A rule set may be either a regular rule set or a <em>fraction rule set,</em> depending
  * on whether it is used to format a number's integral part (or the whole number) or a
  * number's fractional part. Using a rule set to format a rule's fractional part makes it a
  * fraction rule set.</p>
  *
  * <p>Which rule is used to format a number is defined according to one of the following
  * algorithms: If the rule set is a regular rule set, do the following:
  *
  * <ul>
  *   <li>If the rule set includes a default rule (and the number was passed in as a <tt>double</tt>),
  *     use the default rule.&nbsp; (If the number being formatted was passed in as a <tt>long</tt>,
  *     the default rule is ignored.)</li>
  *   <li>If the number is negative, use the negative-number rule.</li>
  *   <li>If the number has a fractional part and is greater than 1, use the improper fraction
  *     rule.</li>
  *   <li>If the number has a fractional part and is between 0 and 1, use the proper fraction
  *     rule.</li>
  *   <li>Binary-search the rule list for the rule with the highest base value less than or equal
  *     to the number. If that rule has two substitutions, its base value is not an even multiple
  *     of its divisor, and the number <em>is</em> an even multiple of the rule's divisor, use the
  *     rule that precedes it in the rule list. Otherwise, use the rule itself.</li>
  * </ul>
  *
  * <p>If the rule set is a fraction rule set, do the following:
  *
  * <ul>
  *   <li>Ignore negative-number and fraction rules.</li>
  *   <li>For each rule in the list, multiply the number being formatted (which will always be
  *     between 0 and 1) by the rule's base value. Keep track of the distance between the result
  *     the nearest integer.</li>
  *   <li>Use the rule that produced the result closest to zero in the above calculation. In the
  *     event of a tie or a direct hit, use the first matching rule encountered. (The idea here is
  *     to try each rule's base value as a possible denominator of a fraction. Whichever
  *     denominator produces the fraction closest in value to the number being formatted wins.) If
  *     the rule following the matching rule has the same base value, use it if the numerator of
  *     the fraction is anything other than 1; if the numerator is 1, use the original matching
  *     rule. (This is to allow singular and plural forms of the rule text without a lot of extra
  *     hassle.)</li>
  * </ul>
  *
  * <p>A rule's body consists of a string of characters terminated by a semicolon. The rule
  * may include zero, one, or two <em>substitution tokens,</em> and a range of text in
  * brackets. The brackets denote optional text (and may also include one or both
  * substitutions). The exact meanings of the substitution tokens, and under what conditions
  * optional text is omitted, depend on the syntax of the substitution token and the context.
  * The rest of the text in a rule body is literal text that is output when the rule matches
  * the number being formatted.</p>
  *
  * <p>A substitution token begins and ends with a <em>token character.</em> The token
  * character and the context together specify a mathematical operation to be performed on the
  * number being formatted. An optional <em>substitution descriptor </em>specifies how the
  * value resulting from that operation is used to fill in the substitution. The position of
  * the substitution token in the rule body specifies the location of the resultant text in
  * the original rule text.</p>
  *
  * <p>The meanings of the substitution token characters are as follows:</p>
  *
  * <table border="0" width="100%">
  *   <tr>
  *     <td>&gt;&gt;</td>
  *     <td>in normal rule</td>
  *     <td>Divide the number by the rule's divisor and format the remainder</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in negative-number rule</td>
  *     <td>Find the absolute value of the number and format the result</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in fraction or default rule</td>
  *     <td>Isolate the number's fractional part and format it.</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in rule in fraction rule set</td>
  *     <td>Not allowed.</td>
  *   </tr>
  *   <tr>
  *     <td>&gt;&gt;&gt;</td>
  *     <td>in normal rule</td>
  *     <td>Divide the number by the rule's divisor and format the remainder,
  *       but bypass the normal rule-selection process and just use the
  *       rule that precedes this one in this rule list.</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in all other rules</td>
  *     <td>Not allowed.</td>
  *   </tr>
  *   <tr>
  *     <td>&lt;&lt;</td>
  *     <td>in normal rule</td>
  *     <td>Divide the number by the rule's divisor, perform floor() on the quotient,
  *         and format the resulting value.<br>
  *         If there is a DecimalFormat pattern between the &lt; characters and the
  *         rule does NOT also contain a &gt;&gt; substitution, we DON'T perform
  *         floor() on the quotient-- the quotient is passed through to the DecimalFormat
  *         intact.  That is, for the value 1,900:<br>
  *         - "1/1000: &lt;&lt; thousand;" will produce "one thousand"<br>
  *         - "1/1000: &lt;0&lt; thousand;" will produce "2 thousand" (NOT "1 thousand")<br>
  *         - "1/1000: &lt;0&lt; seconds &gt;0&gt; milliseconds;" will produce "1 second 900 milliseconds"
  *     </td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in negative-number rule</td>
  *     <td>Not allowed.</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in fraction or default rule</td>
  *     <td>Isolate the number's integral part and format it.</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in rule in fraction rule set</td>
  *     <td>Multiply the number by the rule's base value and format the result.</td>
  *   </tr>
  *   <tr>
  *     <td>==</td>
  *     <td>in all rule sets</td>
  *     <td>Format the number unchanged</td>
  *   </tr>
  *   <tr>
  *     <td>[]</td>
  *     <td>in normal rule</td>
  *     <td>Omit the optional text if the number is an even multiple of the rule's divisor</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in negative-number rule</td>
  *     <td>Not allowed.</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in improper-fraction rule</td>
  *     <td>Omit the optional text if the number is between 0 and 1 (same as specifying both an
  *     x.x rule and a 0.x rule)</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in default rule</td>
  *     <td>Omit the optional text if the number is an integer (same as specifying both an x.x
  *     rule and an x.0 rule)</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in proper-fraction rule</td>
  *     <td>Not allowed.</td>
  *   </tr>
  *   <tr>
  *     <td></td>
  *     <td>in rule in fraction rule set</td>
  *     <td>Omit the optional text if multiplying the number by the rule's base value yields 1.</td>
  *   </tr>
  *   <tr>
  *     <td width="37">$(cardinal,<i>plural syntax</i>)$</td>
  *     <td width="23"></td>
  *     <td width="165" valign="top">in all rule sets</td>
  *     <td>This provides the ability to choose a word based on the number divided by the radix to the power of the
  *     exponent of the base value for the specified locale, which is normally equivalent to the &lt;&lt; value.
  *     This uses the cardinal plural rules from PluralFormat. All strings used in the plural format are treated
  *     as the same base value for parsing.</td>
  *   </tr>
  *   <tr>
  *     <td width="37">$(ordinal,<i>plural syntax</i>)$</td>
  *     <td width="23"></td>
  *     <td width="165" valign="top">in all rule sets</td>
  *     <td>This provides the ability to choose a word based on the number divided by the radix to the power of the
  *     exponent of the base value for the specified locale, which is normally equivalent to the &lt;&lt; value.
  *     This uses the ordinal plural rules from PluralFormat. All strings used in the plural format are treated
  *     as the same base value for parsing.</td>
  *   </tr>
  * </table>
  *
  * <p>The substitution descriptor (i.e., the text between the token characters) may take one
  * of three forms:</p>
  *
  * <table border="0" width="100%">
  *   <tr>
  *     <td>a rule set name</td>
  *     <td>Perform the mathematical operation on the number, and format the result using the
  *     named rule set.</td>
  *   </tr>
  *   <tr>
  *     <td>a DecimalFormat pattern</td>
  *     <td>Perform the mathematical operation on the number, and format the result using a
  *     DecimalFormat with the specified pattern.&nbsp; The pattern must begin with 0 or #.</td>
  *   </tr>
  *   <tr>
  *     <td>nothing</td>
  *     <td>Perform the mathematical operation on the number, and format the result using the rule
  *     set containing the current rule, except:
  *     <ul>
  *       <li>You can't have an empty substitution descriptor with a == substitution.</li>
  *       <li>If you omit the substitution descriptor in a &gt;&gt; substitution in a fraction rule,
  *         format the result one digit at a time using the rule set containing the current rule.</li>
  *       <li>If you omit the substitution descriptor in a &lt;&lt; substitution in a rule in a
  *         fraction rule set, format the result using the default rule set for this formatter.</li>
  *     </ul>
  *     </td>
  *   </tr>
  * </table>
  *
  * <p>Whitespace is ignored between a rule set name and a rule set body, between a rule
  * descriptor and a rule body, or between rules. If a rule body begins with an apostrophe,
  * the apostrophe is ignored, but all text after it becomes significant (this is how you can
  * have a rule's rule text begin with whitespace). There is no escape function: the semicolon
  * is not allowed in rule set names or in rule text, and the colon is not allowed in rule set
  * names. The characters beginning a substitution token are always treated as the beginning
  * of a substitution token.</p>
  *
  * <p>See the resource data and the demo program for annotated examples of real rule sets
  * using these features.</p>
  *
  * <p><em>User subclasses are not supported.</em> While clients may write
  * subclasses, such code will not necessarily work and will not be
  * guaranteed to work stably from release to release.
  *
  * <p><b>Localizations</b></p>
  * <p>Constructors are available that allow the specification of localizations for the
  * public rule sets (and also allow more control over what public rule sets are available).
  * Localization data is represented as a textual description.  The description represents
  * an array of arrays of string.  The first element is an array of the public rule set names,
  * each of these must be one of the public rule set names that appear in the rules.  Only
  * names in this array will be treated as public rule set names by the API.  Each subsequent
  * element is an array of localizations of these names.  The first element of one of these
  * subarrays is the locale name, and the remaining elements are localizations of the
  * public rule set names, in the same order as they were listed in the first array.</p>
  * <p>In the syntax, angle brackets '<', '>' are used to delimit the arrays, and comma ',' is used
  * to separate elements of an array.  Whitespace is ignored, unless quoted.</p>
  * <p>For example:<pre>
  * < < %foo, %bar, %baz >,
  *   < en, Foo, Bar, Baz >,
  *   < fr, 'le Foo', 'le Bar', 'le Baz' >
  *   < zh, \\u7532, \\u4e59, \\u4e19 > >
  * </pre></p>
  * @author Richard Gillam
  * @see NumberFormat
  * @see DecimalFormat
  * @see PluralFormat
  * @see PluralRules
  * @stable ICU 2.0
  */
 class U_I18N_API RuleBasedNumberFormat : public NumberFormat {
 public:
 
   //-----------------------------------------------------------------------
   // constructors
   //-----------------------------------------------------------------------
 
     /**
      * Creates a RuleBasedNumberFormat that behaves according to the description
      * passed in.  The formatter uses the default locale.
      * @param rules A description of the formatter's desired behavior.
      * See the class documentation for a complete explanation of the description
      * syntax.
      * @param perror The parse error if an error was encountered.
      * @param status The status indicating whether the constructor succeeded.
      * @stable ICU 3.2
      */
     RuleBasedNumberFormat(const UnicodeString& rules, UParseError& perror, UErrorCode& status);
 
     /**
      * Creates a RuleBasedNumberFormat that behaves according to the description
      * passed in.  The formatter uses the default locale.
      * <p>
      * The localizations data provides information about the public
      * rule sets and their localized display names for different
      * locales. The first element in the list is an array of the names
      * of the public rule sets.  The first element in this array is
      * the initial default ruleset.  The remaining elements in the
      * list are arrays of localizations of the names of the public
      * rule sets.  Each of these is one longer than the initial array,
      * with the first String being the ULocale ID, and the remaining
      * Strings being the localizations of the rule set names, in the
      * same order as the initial array.  Arrays are nullptr-terminated.
      * @param rules A description of the formatter's desired behavior.
      * See the class documentation for a complete explanation of the description
      * syntax.
      * @param localizations the localization information.
      * names in the description.  These will be copied by the constructor.
      * @param perror The parse error if an error was encountered.
      * @param status The status indicating whether the constructor succeeded.
      * @stable ICU 3.2
      */
     RuleBasedNumberFormat(const UnicodeString& rules, const UnicodeString& localizations,
                         UParseError& perror, UErrorCode& status);
 
   /**
    * Creates a RuleBasedNumberFormat that behaves according to the rules
    * passed in.  The formatter uses the specified locale to determine the
    * characters to use when formatting numerals, and to define equivalences
    * for lenient parsing.
    * @param rules The formatter rules.
    * See the class documentation for a complete explanation of the rule
    * syntax.
    * @param locale A locale that governs which characters are used for
    * formatting values in numerals and which characters are equivalent in
    * lenient parsing.
    * @param perror The parse error if an error was encountered.
    * @param status The status indicating whether the constructor succeeded.
    * @stable ICU 2.0
    */
   RuleBasedNumberFormat(const UnicodeString& rules, const Locale& locale,
                         UParseError& perror, UErrorCode& status);
 
     /**
      * Creates a RuleBasedNumberFormat that behaves according to the description
      * passed in.  The formatter uses the default locale.
      * <p>
      * The localizations data provides information about the public
      * rule sets and their localized display names for different
      * locales. The first element in the list is an array of the names
      * of the public rule sets.  The first element in this array is
      * the initial default ruleset.  The remaining elements in the
      * list are arrays of localizations of the names of the public
      * rule sets.  Each of these is one longer than the initial array,
      * with the first String being the ULocale ID, and the remaining
      * Strings being the localizations of the rule set names, in the
      * same order as the initial array.  Arrays are nullptr-terminated.
      * @param rules A description of the formatter's desired behavior.
      * See the class documentation for a complete explanation of the description
      * syntax.
      * @param localizations a list of localizations for the rule set
      * names in the description.  These will be copied by the constructor.
      * @param locale A locale that governs which characters are used for
      * formatting values in numerals and which characters are equivalent in
      * lenient parsing.
      * @param perror The parse error if an error was encountered.
      * @param status The status indicating whether the constructor succeeded.
      * @stable ICU 3.2
      */
     RuleBasedNumberFormat(const UnicodeString& rules, const UnicodeString& localizations,
                         const Locale& locale, UParseError& perror, UErrorCode& status);
 
   /**
    * Creates a RuleBasedNumberFormat from a predefined ruleset.  The selector
    * code chose among three possible predefined formats: spellout, ordinal,
    * and duration.
    * @param tag A selector code specifying which kind of formatter to create for that
    * locale.  There are four legal values: URBNF_SPELLOUT, which creates a formatter that
    * spells out a value in words in the desired language, URBNF_ORDINAL, which attaches
    * an ordinal suffix from the desired language to the end of a number (e.g. "123rd"),
    * URBNF_DURATION, which formats a duration in seconds as hours, minutes, and seconds always rounding down,
    * and URBNF_NUMBERING_SYSTEM, which is used to invoke rules for alternate numbering
    * systems such as the Hebrew numbering system, or for Roman Numerals, etc.
    * NOTE: If you use URBNF_NUMBERING_SYSTEM, you must also call setDefaultRuleSet() to
    * specify the exact numbering system you want to use.  If you want the default numbering system
    * for the locale, call NumberFormat::createInstance() instead of creating a RuleBasedNumberFormat directly.
    * @param locale The locale for the formatter.
    * @param status The status indicating whether the constructor succeeded.
    * @stable ICU 2.0
    */
   RuleBasedNumberFormat(URBNFRuleSetTag tag, const Locale& locale, UErrorCode& status);
 
   //-----------------------------------------------------------------------
   // boilerplate
   //-----------------------------------------------------------------------
 
   /**
    * Copy constructor
    * @param rhs    the object to be copied from.
    * @stable ICU 2.6
    */
   RuleBasedNumberFormat(const RuleBasedNumberFormat& rhs);
 
   /**
    * Assignment operator
    * @param rhs    the object to be copied from.
    * @stable ICU 2.6
    */
   RuleBasedNumberFormat& operator=(const RuleBasedNumberFormat& rhs);
 
   /**
    * Release memory allocated for a RuleBasedNumberFormat when you are finished with it.
    * @stable ICU 2.6
    */
   virtual ~RuleBasedNumberFormat();
 
   /**
    * Clone this object polymorphically.  The caller is responsible
    * for deleting the result when done.
    * @return  A copy of the object.
    * @stable ICU 2.6
    */
   virtual RuleBasedNumberFormat* clone() const override;
 
   /**
    * Return true if the given Format objects are semantically equal.
    * Objects of different subclasses are considered unequal.
    * @param other    the object to be compared with.
    * @return        true if the given Format objects are semantically equal.
    * @stable ICU 2.6
    */
   virtual bool operator==(const Format& other) const override;
 
 //-----------------------------------------------------------------------
 // public API functions
 //-----------------------------------------------------------------------
 
   /**
    * return the rules that were provided to the RuleBasedNumberFormat.
    * @return the result String that was passed in
    * @stable ICU 2.0
    */
   virtual UnicodeString getRules() const;
 
   /**
    * Return the number of public rule set names.
    * @return the number of public rule set names.
    * @stable ICU 2.0
    */
   virtual int32_t getNumberOfRuleSetNames() const;
 
   /**
    * Return the name of the index'th public ruleSet.  If index is not valid,
    * the function returns null.
    * @param index the index of the ruleset
    * @return the name of the index'th public ruleSet.
    * @stable ICU 2.0
    */
   virtual UnicodeString getRuleSetName(int32_t index) const;
 
   /**
    * Return the number of locales for which we have localized rule set display names.
    * @return the number of locales for which we have localized rule set display names.
    * @stable ICU 3.2
    */
   virtual int32_t getNumberOfRuleSetDisplayNameLocales() const;
 
   /**
    * Return the index'th display name locale.
    * @param index the index of the locale
    * @param status set to a failure code when this function fails
    * @return the locale
    * @see #getNumberOfRuleSetDisplayNameLocales
    * @stable ICU 3.2
    */
   virtual Locale getRuleSetDisplayNameLocale(int32_t index, UErrorCode& status) const;
 
     /**
      * Return the rule set display names for the provided locale.  These are in the same order
      * as those returned by getRuleSetName.  The locale is matched against the locales for
      * which there is display name data, using normal fallback rules.  If no locale matches,
      * the default display names are returned.  (These are the internal rule set names minus
      * the leading '%'.)
      * @param index the index of the rule set
      * @param locale the locale (returned by getRuleSetDisplayNameLocales) for which the localized
      * display name is desired
      * @return the display name for the given index, which might be bogus if there is an error
      * @see #getRuleSetName
      * @stable ICU 3.2
      */
   virtual UnicodeString getRuleSetDisplayName(int32_t index,
                           const Locale& locale = Locale::getDefault());
 
     /**
      * Return the rule set display name for the provided rule set and locale.
      * The locale is matched against the locales for which there is display name data, using
      * normal fallback rules.  If no locale matches, the default display name is returned.
      * @return the display name for the rule set
      * @stable ICU 3.2
      * @see #getRuleSetDisplayName
      */
   virtual UnicodeString getRuleSetDisplayName(const UnicodeString& ruleSetName,
                           const Locale& locale = Locale::getDefault());
 
 
   using NumberFormat::format;
 
   /**
    * Formats the specified 32-bit number using the default ruleset.
    * @param number The number to format.
    * @param toAppendTo the string that will hold the (appended) result
    * @param pos the fieldposition
    * @return A textual representation of the number.
    * @stable ICU 2.0
    */
   virtual UnicodeString& format(int32_t number,
                                 UnicodeString& toAppendTo,
                                 FieldPosition& pos) const override;
 
   /**
    * Formats the specified 64-bit number using the default ruleset.
    * @param number The number to format.
    * @param toAppendTo the string that will hold the (appended) result
    * @param pos the fieldposition
    * @return A textual representation of the number.
    * @stable ICU 2.1
    */
   virtual UnicodeString& format(int64_t number,
                                 UnicodeString& toAppendTo,
                                 FieldPosition& pos) const override;
   /**
    * Formats the specified number using the default ruleset.
    * @param number The number to format.
    * @param toAppendTo the string that will hold the (appended) result
    * @param pos the fieldposition
    * @return A textual representation of the number.
    * @stable ICU 2.0
    */
   virtual UnicodeString& format(double number,
                                 UnicodeString& toAppendTo,
                                 FieldPosition& pos) const override;
 
   /**
    * Formats the specified number using the named ruleset.
    * @param number The number to format.
    * @param ruleSetName The name of the rule set to format the number with.
    * This must be the name of a valid public rule set for this formatter.
    * @param toAppendTo the string that will hold the (appended) result
    * @param pos the fieldposition
    * @param status the status
    * @return A textual representation of the number.
    * @stable ICU 2.0
    */
   virtual UnicodeString& format(int32_t number,
                                 const UnicodeString& ruleSetName,
                                 UnicodeString& toAppendTo,
                                 FieldPosition& pos,
                                 UErrorCode& status) const;
   /**
    * Formats the specified 64-bit number using the named ruleset.
    * @param number The number to format.
    * @param ruleSetName The name of the rule set to format the number with.
    * This must be the name of a valid public rule set for this formatter.
    * @param toAppendTo the string that will hold the (appended) result
    * @param pos the fieldposition
    * @param status the status
    * @return A textual representation of the number.
    * @stable ICU 2.1
    */
   virtual UnicodeString& format(int64_t number,
                                 const UnicodeString& ruleSetName,
                                 UnicodeString& toAppendTo,
                                 FieldPosition& pos,
                                 UErrorCode& status) const;
   /**
    * Formats the specified number using the named ruleset.
    * @param number The number to format.
    * @param ruleSetName The name of the rule set to format the number with.
    * This must be the name of a valid public rule set for this formatter.
    * @param toAppendTo the string that will hold the (appended) result
    * @param pos the fieldposition
    * @param status the status
    * @return A textual representation of the number.
    * @stable ICU 2.0
    */
   virtual UnicodeString& format(double number,
                                 const UnicodeString& ruleSetName,
                                 UnicodeString& toAppendTo,
                                 FieldPosition& pos,
                                 UErrorCode& status) const;
 
 protected:
     /**
      * Format a decimal number.
      * The number is a DigitList wrapper onto a floating point decimal number.
      * The default implementation in NumberFormat converts the decimal number
      * to a double and formats that.  Subclasses of NumberFormat that want
      * to specifically handle big decimal numbers must override this method.
      * class DecimalFormat does so.
      *
      * @param number    The number, a DigitList format Decimal Floating Point.
      * @param appendTo  Output parameter to receive result.
      *                  Result is appended to existing contents.
      * @param pos       On input: an alignment field, if desired.
      *                  On output: the offsets of the alignment field.
      * @param status    Output param filled with success/failure status.
      * @return          Reference to 'appendTo' parameter.
      * @internal
      */
     virtual UnicodeString& format(const number::impl::DecimalQuantity &number,
                                   UnicodeString& appendTo,
                                   FieldPosition& pos,
                                   UErrorCode& status) const override;
 public:
 
   using NumberFormat::parse;
 
   /**
    * Parses the specified string, beginning at the specified position, according
    * to this formatter's rules.  This will match the string against all of the
    * formatter's public rule sets and return the value corresponding to the longest
    * parseable substring.  This function's behavior is affected by the lenient
    * parse mode.
    * @param text The string to parse
    * @param result the result of the parse, either a double or a long.
    * @param parsePosition On entry, contains the position of the first character
    * in "text" to examine.  On exit, has been updated to contain the position
    * of the first character in "text" that wasn't consumed by the parse.
    * @see #setLenient
    * @stable ICU 2.0
    */
   virtual void parse(const UnicodeString& text,
                      Formattable& result,
                      ParsePosition& parsePosition) const override;
 
 #if !UCONFIG_NO_COLLATION
 
   /**
    * Turns lenient parse mode on and off.
    *
    * When in lenient parse mode, the formatter uses a Collator for parsing the text.
    * Only primary differences are treated as significant.  This means that case
    * differences, accent differences, alternate spellings of the same letter
    * (e.g., ae and a-umlaut in German), ignorable characters, etc. are ignored in
    * matching the text.  In many cases, numerals will be accepted in place of words
    * or phrases as well.
    *
    * For example, all of the following will correctly parse as 255 in English in
    * lenient-parse mode:
    * <br>"two hundred fifty-five"
    * <br>"two hundred fifty five"
    * <br>"TWO HUNDRED FIFTY-FIVE"
    * <br>"twohundredfiftyfive"
    * <br>"2 hundred fifty-5"
    *
    * The Collator used is determined by the locale that was
    * passed to this object on construction.  The description passed to this object
    * on construction may supply additional collation rules that are appended to the
    * end of the default collator for the locale, enabling additional equivalences
    * (such as adding more ignorable characters or permitting spelled-out version of
    * symbols; see the demo program for examples).
    *
    * It's important to emphasize that even strict parsing is relatively lenient: it
    * will accept some text that it won't produce as output.  In English, for example,
    * it will correctly parse "two hundred zero" and "fifteen hundred".
    *
    * @param enabled If true, turns lenient-parse mode on; if false, turns it off.
    * @see RuleBasedCollator
    * @stable ICU 2.0
    */
   virtual void setLenient(UBool enabled) override;
 
   /**
    * Returns true if lenient-parse mode is turned on.  Lenient parsing is off
    * by default.
    * @return true if lenient-parse mode is turned on.
    * @see #setLenient
    * @stable ICU 2.0
    */
   virtual inline UBool isLenient() const override;
 
 #endif
 
   /**
    * Override the default rule set to use.  If ruleSetName is null, reset
    * to the initial default rule set.  If the rule set is not a public rule set name,
    * U_ILLEGAL_ARGUMENT_ERROR is returned in status.
    * @param ruleSetName the name of the rule set, or null to reset the initial default.
    * @param status set to failure code when a problem occurs.
    * @stable ICU 2.6
    */
   virtual void setDefaultRuleSet(const UnicodeString& ruleSetName, UErrorCode& status);
 
   /**
    * Return the name of the current default rule set.  If the current rule set is
    * not public, returns a bogus (and empty) UnicodeString.
    * @return the name of the current default rule set
    * @stable ICU 3.0
    */
   virtual UnicodeString getDefaultRuleSetName() const;
 
   /**
    * Set a particular UDisplayContext value in the formatter, such as
    * UDISPCTX_CAPITALIZATION_FOR_STANDALONE. Note: For getContext, see
    * NumberFormat.
    * @param value The UDisplayContext value to set.
    * @param status Input/output status. If at entry this indicates a failure
    *               status, the function will do nothing; otherwise this will be
    *               updated with any new status from the function. 
    * @stable ICU 53
    */
   virtual void setContext(UDisplayContext value, UErrorCode& status) override;
 
     /**
      * Get the rounding mode.
      * @return A rounding mode
      * @stable ICU 60
      */
     virtual ERoundingMode getRoundingMode() const override;
 
     /**
      * Set the rounding mode.
      * @param roundingMode A rounding mode
      * @stable ICU 60
      */
     virtual void setRoundingMode(ERoundingMode roundingMode) override;
 
 public:
     /**
      * ICU "poor man's RTTI", returns a UClassID for this class.
      *
      * @stable ICU 2.8
      */
     static UClassID U_EXPORT2 getStaticClassID();
 
     /**
      * ICU "poor man's RTTI", returns a UClassID for the actual class.
      *
      * @stable ICU 2.8
      */
     virtual UClassID getDynamicClassID() const override;
 
     /**
      * Sets the decimal format symbols, which is generally not changed
      * by the programmer or user. The formatter takes ownership of
      * symbolsToAdopt; the client must not delete it.
      *
      * @param symbolsToAdopt DecimalFormatSymbols to be adopted.
      * @stable ICU 49
      */
     virtual void adoptDecimalFormatSymbols(DecimalFormatSymbols* symbolsToAdopt);
 
     /**
      * Sets the decimal format symbols, which is generally not changed
      * by the programmer or user. A clone of the symbols is created and
      * the symbols is _not_ adopted; the client is still responsible for
      * deleting it.
      *
      * @param symbols DecimalFormatSymbols.
      * @stable ICU 49
      */
     virtual void setDecimalFormatSymbols(const DecimalFormatSymbols& symbols);
 
 private:
     RuleBasedNumberFormat() = delete; // default constructor not implemented
 
     // this will ref the localizations if they are not nullptr
     // caller must deref to get adoption
     RuleBasedNumberFormat(const UnicodeString& description, LocalizationInfo* localizations,
               const Locale& locale, UParseError& perror, UErrorCode& status);
 
     void init(const UnicodeString& rules, LocalizationInfo* localizations, UParseError& perror, UErrorCode& status);
     void initCapitalizationContextInfo(const Locale& thelocale);
     void dispose();
     void stripWhitespace(UnicodeString& src);
     void initDefaultRuleSet();
     NFRuleSet* findRuleSet(const UnicodeString& name, UErrorCode& status) const;
 
     /* friend access */
     friend class NFSubstitution;
     friend class NFRule;
     friend class NFRuleSet;
     friend class FractionalPartSubstitution;
 
     inline NFRuleSet * getDefaultRuleSet() const;
     const RuleBasedCollator * getCollator() const;
     DecimalFormatSymbols * initializeDecimalFormatSymbols(UErrorCode &status);
     const DecimalFormatSymbols * getDecimalFormatSymbols() const;
     NFRule * initializeDefaultInfinityRule(UErrorCode &status);
     const NFRule * getDefaultInfinityRule() const;
     NFRule * initializeDefaultNaNRule(UErrorCode &status);
     const NFRule * getDefaultNaNRule() const;
     PluralFormat *createPluralFormat(UPluralType pluralType, const UnicodeString &pattern, UErrorCode& status) const;
     UnicodeString& adjustForCapitalizationContext(int32_t startPos, UnicodeString& currentResult, UErrorCode& status) const;
     UnicodeString& format(int64_t number, NFRuleSet *ruleSet, UnicodeString& toAppendTo, UErrorCode& status) const;
     void format(double number, NFRuleSet& rs, UnicodeString& toAppendTo, UErrorCode& status) const;
 
 private:
     NFRuleSet **fRuleSets;
     UnicodeString* ruleSetDescriptions;
     int32_t numRuleSets;
     NFRuleSet *defaultRuleSet;
     Locale locale;
     RuleBasedCollator* collator;
     DecimalFormatSymbols* decimalFormatSymbols;
     NFRule *defaultInfinityRule;
     NFRule *defaultNaNRule;
     ERoundingMode fRoundingMode;
     UBool lenient;
     UnicodeString* lenientParseRules;
     LocalizationInfo* localizations;
     UnicodeString originalDescription;
     UBool capitalizationInfoSet;
     UBool capitalizationForUIListMenu;
     UBool capitalizationForStandAlone;
     BreakIterator* capitalizationBrkIter;
 };
 
 // ---------------
 
 #if !UCONFIG_NO_COLLATION
 
 inline UBool
 RuleBasedNumberFormat::isLenient() const {
     return lenient;
 }
 
 #endif
 
 inline NFRuleSet*
 RuleBasedNumberFormat::getDefaultRuleSet() const {
     return defaultRuleSet;
 }
 
 U_NAMESPACE_END
 
 /* U_HAVE_RBNF */
 #endif
 
 #endif /* U_SHOW_CPLUSPLUS_API */
 
 /* RBNF_H */
 #endif

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