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RuleBasedTransliterator Class Reference
RuleBasedTransliterator
is a transliterator that reads a set of rules in order to determine how to perform translations.
More...
#include <rbt.h>
Inheritance diagram for RuleBasedTransliterator:
Public Methods |
| RuleBasedTransliterator (const UnicodeString &id, const UnicodeString &rules, UTransDirection direction, UnicodeFilter *adoptedFilter, UParseError &parseError, UErrorCode &status) |
| Constructs a new transliterator from the given rules. More...
|
| RuleBasedTransliterator (const UnicodeString &id, const UnicodeString &rules, UTransDirection direction, UnicodeFilter *adoptedFilter, UErrorCode &status) |
| Constructs a new transliterator from the given rules. More...
|
| RuleBasedTransliterator (const UnicodeString &id, const UnicodeString &rules, UTransDirection direction, UErrorCode &status) |
| Covenience constructor with no filter. More...
|
| RuleBasedTransliterator (const UnicodeString &id, const UnicodeString &rules, UErrorCode &status) |
| Covenience constructor with no filter and FORWARD direction. More...
|
| RuleBasedTransliterator (const UnicodeString &id, const UnicodeString &rules, UnicodeFilter *adoptedFilter, UErrorCode &status) |
| Covenience constructor with FORWARD direction. More...
|
| RuleBasedTransliterator (const RuleBasedTransliterator &) |
| Copy constructor. More...
|
virtual | ~RuleBasedTransliterator () |
Transliterator * | clone (void) const |
| Implement Transliterator API. More...
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virtual void | handleTransliterate (Replaceable &text, UTransPosition &offsets, UBool isIncremental) const |
| Implements Transliterator::handleTransliterate. More...
|
virtual UnicodeString & | toRules (UnicodeString &result, UBool escapeUnprintable) const |
| Return a representation of this transliterator as source rules. More...
|
virtual UClassID | getDynamicClassID (void) const |
| Returns a unique class ID polymorphically. More...
|
Static Public Methods |
UClassID | getStaticClassID (void) |
| Return the class ID for this class. More...
|
Friends |
class | TransliteratorRegistry |
class | Transliterator |
Detailed Description
RuleBasedTransliterator
is a transliterator that reads a set of rules in order to determine how to perform translations.
Rule sets are stored in resource bundles indexed by name. Rules within a rule set are separated by semicolons (';'). To include a literal semicolon, prefix it with a backslash ('\'). Whitespace, as defined by Character.isWhitespace()
, is ignored. If the first non-blank character on a line is '#', the entire line is ignored as a comment.
Each set of rules consists of two groups, one forward, and one reverse. This is a convention that is not enforced; rules for one direction may be omitted, with the result that translations in that direction will not modify the source text. In addition, bidirectional forward-reverse rules may be specified for symmetrical transformations.
Rule syntax
Rule statements take one of the following forms:
$alefmadda=\u0622;
- Variable definition. The name on the left is assigned the text on the right. In this example, after this statement, instances of the left hand name, "
$alefmadda
", will be replaced by the Unicode character U+0622. Variable names must begin with a letter and consist only of letters, digits, and underscores. Case is significant. Duplicate names cause an exception to be thrown, that is, variables cannot be redefined. The right hand side may contain well-formed text of any length, including no text at all ("$empty=;
"). The right hand side may contain embedded UnicodeSet
patterns, for example, "$softvowel=[eiyEIY]
". -
ai>$alefmadda;
- Forward translation rule. This rule states that the string on the left will be changed to the string on the right when performing forward transliteration.
-
ai<$alefmadda;
- Reverse translation rule. This rule states that the string on the right will be changed to the string on the left when performing reverse transliteration.
ai<>$alefmadda;
- Bidirectional translation rule. This rule states that the string on the right will be changed to the string on the left when performing forward transliteration, and vice versa when performing reverse transliteration.
Translation rules consist of a match pattern and an output string. The match pattern consists of literal characters, optionally preceded by context, and optionally followed by context. Context characters, like literal pattern characters, must be matched in the text being transliterated. However, unlike literal pattern characters, they are not replaced by the output text. For example, the pattern "abc{def}
" indicates the characters "def
" must be preceded by "abc
" for a successful match. If there is a successful match, "def
" will be replaced, but not "abc
". The final '}
' is optional, so "abc{def
" is equivalent to "abc{def}
". Another example is "{123}456
" (or "123}456
") in which the literal pattern "123
" must be followed by "456
".
The output string of a forward or reverse rule consists of characters to replace the literal pattern characters. If the output string contains the character '|
', this is taken to indicate the location of the cursor after replacement. The cursor is the point in the text at which the next replacement, if any, will be applied. The cursor is usually placed within the replacement text; however, it can actually be placed into the precending or following context by using the special character '</code>'. Examples:
a {foo} z > | @ bar; # foo -> bar, move cursor before a
{foo} xyz > bar @|; # foo -> bar, cursor between y and z
UnicodeSet
UnicodeSet
patterns may appear anywhere that makes sense. They may appear in variable definitions. Contrariwise, UnicodeSet
patterns may themselves contain variable references, such as "$a=[a-z];$not_a=[^$a]
", or "$range=a-z;$ll=[$range]
".
UnicodeSet
patterns may also be embedded directly into rule strings. Thus, the following two rules are equivalent:
$vowel=[aeiou]; $vowel>'*'; # One way to do this
[aeiou]>'*'; # Another way
See UnicodeSet for more documentation and examples.
Segments
Segments of the input string can be matched and copied to the output string. This makes certain sets of rules simpler and more general, and makes reordering possible. For example:
([a-z]) > $1 $1; # double lowercase letters
([:Lu:]) ([:Ll:]) > $2 $1; # reverse order of Lu-Ll pairs
The segment of the input string to be copied is delimited by "(
" and ")
". Up to nine segments may be defined. Segments may not overlap. In the output string, "$1
" through "$9
" represent the input string segments, in left-to-right order of definition.
Anchors
Patterns can be anchored to the beginning or the end of the text. This is done with the special characters '^
' and '$
'. For example:
^ a > 'BEG_A'; # match 'a' at start of text
a > 'A'; # match other instances of 'a'
z $ > 'END_Z'; # match 'z' at end of text
z > 'Z'; # match other instances of 'z'
It is also possible to match the beginning or the end of the text using a UnicodeSet
. This is done by including a virtual anchor character '$
' at the end of the set pattern. Although this is usually the match chafacter for the end anchor, the set will match either the beginning or the end of the text, depending on its placement. For example:
$x = [a-z$]; # match 'a' through 'z' OR anchor
$x 1 > 2; # match '1' after a-z or at the start
3 $x > 4; # match '3' before a-z or at the end
Example
The following example rules illustrate many of the features of the rule language.
Rule 1. | abc{def}>x|y |
Rule 2. | xyz>r |
Rule 3. | yz>q |
Applying these rules to the string "adefabcdefz
" yields the following results:
|adefabcdefz | Initial state, no rules match. Advance cursor. |
a|defabcdefz | Still no match. Rule 1 does not match because the preceding context is not present. |
ad|efabcdefz | Still no match. Keep advancing until there is a match... |
ade|fabcdefz | ... |
adef|abcdefz | ... |
adefa|bcdefz | ... |
adefab|cdefz | ... |
adefabc|defz | Rule 1 matches; replace "def " with "xy " and back up the cursor to before the 'y '. |
adefabcx|yz | Although "xyz " is present, rule 2 does not match because the cursor is before the 'y ', not before the 'x '. Rule 3 does match. Replace "yz " with "q ". |
adefabcxq| | The cursor is at the end; transliteration is complete. |
The order of rules is significant. If multiple rules may match at some point, the first matching rule is applied.
Forward and reverse rules may have an empty output string. Otherwise, an empty left or right hand side of any statement is a syntax error.
Single quotes are used to quote any character other than a digit or letter. To specify a single quote itself, inside or outside of quotes, use two single quotes in a row. For example, the rule "'>'>o''clock
" changes the string ">
" to the string "o'clock
".
Notes
While a RuleBasedTransliterator is being built, it checks that the rules are added in proper order. For example, if the rule "a>x" is followed by the rule "ab>y", then the second rule will throw an exception. The reason is that the second rule can never be triggered, since the first rule always matches anything it matches. In other words, the first rule masks the second rule.
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Author:
-
Alan Liu
-
Deprecated:
-
To be removed after 2002-sep-30; use the Transliterator::createFromRules factory method.
Constructor & Destructor Documentation
|
Constructs a new transliterator from the given rules.
-
Parameters:
-
rules |
rules, separated by ';' |
direction |
either FORWARD or REVERSE. |
-
Exceptions:
-
IllegalArgumentException |
if rules are malformed. |
-
Deprecated:
-
To be removed after 2002-sep-30; use the Transliterator::createFromRules factory method.
|
|
Constructs a new transliterator from the given rules.
-
Parameters:
-
rules |
rules, separated by ';' |
direction |
either FORWARD or REVERSE. |
-
Exceptions:
-
IllegalArgumentException |
if rules are malformed. |
-
Deprecated:
-
To be removed after 2002-sep-30; use the Transliterator::createFromRules factory method.
|
|
Covenience constructor with no filter and FORWARD direction.
-
Deprecated:
-
To be removed after 2002-sep-30; use the Transliterator::createFromRules factory method.
|
RuleBasedTransliterator::RuleBasedTransliterator |
( |
const RuleBasedTransliterator & |
|
) |
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|
Member Function Documentation
Transliterator* RuleBasedTransliterator::clone |
( |
void |
|
) |
const [virtual] |
|
virtual UClassID RuleBasedTransliterator::getDynamicClassID |
( |
void |
|
) |
const [inline, virtual] |
|
|
Returns a unique class ID polymorphically.
This method is to implement a simple version of RTTI, since not all C++ compilers support genuine RTTI. Polymorphic operator==() and clone() methods call this method.
Concrete subclasses of Transliterator that wish clients to be able to identify them should implement getDynamicClassID() and also a static method and data member:
static UClassID getStaticClassID() { return (UClassID)&fgClassID; }
static char fgClassID;
Subclasses that do not implement this method will have a dynamic class ID of Transliterator::getStatisClassID().
-
Returns:
-
The class ID for this object. All objects of a given class have the same class ID. Objects of other classes have different class IDs.
Reimplemented from Transliterator. |
UClassID RuleBasedTransliterator::getStaticClassID |
( |
void |
|
) |
[inline, static] |
|
|
Return the class ID for this class.
This is useful only for comparing to a return value from getDynamicClassID(). For example:
. Base* polymorphic_pointer = createPolymorphicObject();
. if (polymorphic_pointer->getDynamicClassID() ==
. Derived::getStaticClassID()) ...
-
Returns:
-
The class ID for all objects of this class.
-
Deprecated:
-
To be removed after 2002-sep-30.
Reimplemented from Transliterator. |
virtual void RuleBasedTransliterator::handleTransliterate |
( |
Replaceable & |
text, |
|
|
UTransPosition & |
offsets, |
|
|
UBool |
isIncremental |
|
) |
const [virtual] |
|
|
Return a representation of this transliterator as source rules.
These rules will produce an equivalent transliterator if used to construct a new transliterator. -
Parameters:
-
result |
the string to receive the rules. Previous contents will be deleted. |
escapeUnprintable |
if TRUE then convert unprintable character to their hex escape representations, \uxxxx or \Uxxxxxxxx. Unprintable characters are those other than U+000A, U+0020..U+007E. |
-
Deprecated:
-
To be removed after 2002-sep-30; use the Transliterator::toRules directly.
Reimplemented from Transliterator. |
The documentation for this class was generated from the following file:
Generated on Tue Mar 5 13:05:57 2002 for ICU 2.0 by
1.2.14 written by Dimitri van Heesch,
© 1997-2002