Revision control
Copy as Markdown
Other Tools
// Copyright 2023 The Mozilla Foundation. See the
// COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use super::TextSource;
use alloc::borrow::Cow;
use alloc::vec::Vec;
use core::char;
use core::ops::Range;
use crate::{
compute_bidi_info_for_para, compute_initial_info, level, para_direction, reorder_levels,
reorder_visual, visual_runs_for_line,
};
use crate::{
BidiClass, BidiDataSource, Direction, Level, LevelRun, ParagraphInfo, ParagraphInfoFlags,
};
#[cfg(feature = "hardcoded-data")]
use crate::HardcodedBidiData;
/// Initial bidi information of the text (UTF-16 version).
///
/// Contains the text paragraphs and `BidiClass` of its characters.
#[derive(PartialEq, Debug)]
pub struct InitialInfo<'text> {
/// The text
pub text: &'text [u16],
/// The BidiClass of the character at each code unit in the text.
/// If a character is multiple code units, its class will appear multiple times in the vector.
pub original_classes: Vec<BidiClass>,
/// The boundaries and level of each paragraph within the text.
pub paragraphs: Vec<ParagraphInfo>,
}
impl<'text> InitialInfo<'text> {
/// Find the paragraphs and BidiClasses in a string of text.
///
///
/// Also sets the class for each First Strong Isolate initiator (FSI) to LRI or RLI if a strong
/// character is found before the matching PDI. If no strong character is found, the class will
/// remain FSI, and it's up to later stages to treat these as LRI when needed.
///
/// The `hardcoded-data` Cargo feature (enabled by default) must be enabled to use this.
#[cfg_attr(feature = "flame_it", flamer::flame)]
#[cfg(feature = "hardcoded-data")]
pub fn new(text: &[u16], default_para_level: Option<Level>) -> InitialInfo<'_> {
Self::new_with_data_source(&HardcodedBidiData, text, default_para_level)
}
/// Find the paragraphs and BidiClasses in a string of text, with a custom [`BidiDataSource`]
/// for Bidi data. If you just wish to use the hardcoded Bidi data, please use [`InitialInfo::new()`]
/// instead (enabled with tbe default `hardcoded-data` Cargo feature)
///
///
/// Also sets the class for each First Strong Isolate initiator (FSI) to LRI or RLI if a strong
/// character is found before the matching PDI. If no strong character is found, the class will
/// remain FSI, and it's up to later stages to treat these as LRI when needed.
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn new_with_data_source<'a, D: BidiDataSource>(
data_source: &D,
text: &'a [u16],
default_para_level: Option<Level>,
) -> InitialInfo<'a> {
InitialInfoExt::new_with_data_source(data_source, text, default_para_level).base
}
}
/// Extended version of InitialInfo (not public API).
#[derive(PartialEq, Debug)]
struct InitialInfoExt<'text> {
/// The base InitialInfo for the text, recording its paragraphs and bidi classes.
base: InitialInfo<'text>,
/// Parallel to base.paragraphs, records whether each paragraph is "pure LTR" that
/// requires no further bidi processing (i.e. there are no RTL characters or bidi
/// control codes present).
flags: Vec<ParagraphInfoFlags>,
}
impl<'text> InitialInfoExt<'text> {
/// Find the paragraphs and BidiClasses in a string of text, with a custom [`BidiDataSource`]
/// for Bidi data. If you just wish to use the hardcoded Bidi data, please use [`InitialInfo::new()`]
/// instead (enabled with tbe default `hardcoded-data` Cargo feature)
///
///
/// Also sets the class for each First Strong Isolate initiator (FSI) to LRI or RLI if a strong
/// character is found before the matching PDI. If no strong character is found, the class will
/// remain FSI, and it's up to later stages to treat these as LRI when needed.
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn new_with_data_source<'a, D: BidiDataSource>(
data_source: &D,
text: &'a [u16],
default_para_level: Option<Level>,
) -> InitialInfoExt<'a> {
let mut paragraphs = Vec::<ParagraphInfo>::new();
let mut flags = Vec::<ParagraphInfoFlags>::new();
let (original_classes, _, _, _) = compute_initial_info(
data_source,
text,
default_para_level,
Some((&mut paragraphs, &mut flags)),
);
InitialInfoExt {
base: InitialInfo {
text,
original_classes,
paragraphs,
},
flags,
}
}
}
/// Bidi information of the text (UTF-16 version).
///
/// The `original_classes` and `levels` vectors are indexed by code unit offsets into the text. If a
/// character is multiple code units wide, then its class and level will appear multiple times in these
/// vectors.
// TODO: Impl `struct StringProperty<T> { values: Vec<T> }` and use instead of Vec<T>
#[derive(Debug, PartialEq)]
pub struct BidiInfo<'text> {
/// The text
pub text: &'text [u16],
/// The BidiClass of the character at each byte in the text.
pub original_classes: Vec<BidiClass>,
/// The directional embedding level of each byte in the text.
pub levels: Vec<Level>,
/// The boundaries and paragraph embedding level of each paragraph within the text.
///
/// TODO: Use SmallVec or similar to avoid overhead when there are only one or two paragraphs?
/// Or just don't include the first paragraph, which always starts at 0?
pub paragraphs: Vec<ParagraphInfo>,
}
impl<'text> BidiInfo<'text> {
/// Split the text into paragraphs and determine the bidi embedding levels for each paragraph.
///
///
/// The `hardcoded-data` Cargo feature (enabled by default) must be enabled to use this.
///
/// TODO: In early steps, check for special cases that allow later steps to be skipped. like
/// text that is entirely LTR. See the `nsBidi` class from Gecko for comparison.
///
/// TODO: Support auto-RTL base direction
#[cfg_attr(feature = "flame_it", flamer::flame)]
#[cfg(feature = "hardcoded-data")]
#[inline]
pub fn new(text: &[u16], default_para_level: Option<Level>) -> BidiInfo<'_> {
Self::new_with_data_source(&HardcodedBidiData, text, default_para_level)
}
/// Split the text into paragraphs and determine the bidi embedding levels for each paragraph, with a custom [`BidiDataSource`]
/// for Bidi data. If you just wish to use the hardcoded Bidi data, please use [`BidiInfo::new()`]
/// instead (enabled with tbe default `hardcoded-data` Cargo feature).
///
/// TODO: In early steps, check for special cases that allow later steps to be skipped. like
/// text that is entirely LTR. See the `nsBidi` class from Gecko for comparison.
///
/// TODO: Support auto-RTL base direction
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn new_with_data_source<'a, D: BidiDataSource>(
data_source: &D,
text: &'a [u16],
default_para_level: Option<Level>,
) -> BidiInfo<'a> {
let InitialInfoExt { base, flags, .. } =
InitialInfoExt::new_with_data_source(data_source, text, default_para_level);
let mut levels = Vec::<Level>::with_capacity(text.len());
let mut processing_classes = base.original_classes.clone();
for (para, flags) in base.paragraphs.iter().zip(flags.iter()) {
let text = &text[para.range.clone()];
let original_classes = &base.original_classes[para.range.clone()];
compute_bidi_info_for_para(
data_source,
para,
flags.is_pure_ltr,
flags.has_isolate_controls,
text,
original_classes,
&mut processing_classes,
&mut levels,
);
}
BidiInfo {
text,
original_classes: base.original_classes,
paragraphs: base.paragraphs,
levels,
}
}
/// Produce the levels for this paragraph as needed for reordering, one level per *byte*
/// in the paragraph. The returned vector includes bytes that are not included
/// in the `line`, but will not adjust them.
///
/// This runs [Rule L1], you can run
/// [Rule L2] by calling [`Self::reorder_visual()`].
/// If doing so, you may prefer to use [`Self::reordered_levels_per_char()`] instead
/// to avoid non-byte indices.
///
/// For an all-in-one reordering solution, consider using [`Self::reorder_visual()`].
///
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn reordered_levels(&self, para: &ParagraphInfo, line: Range<usize>) -> Vec<Level> {
assert!(line.start <= self.levels.len());
assert!(line.end <= self.levels.len());
let mut levels = self.levels.clone();
let line_classes = &self.original_classes[line.clone()];
let line_levels = &mut levels[line.clone()];
let line_str: &[u16] = &self.text[line.clone()];
reorder_levels(line_classes, line_levels, line_str, para.level);
levels
}
/// Produce the levels for this paragraph as needed for reordering, one level per *character*
/// in the paragraph. The returned vector includes characters that are not included
/// in the `line`, but will not adjust them.
///
/// This runs [Rule L1], you can run
/// [Rule L2] by calling [`Self::reorder_visual()`].
/// If doing so, you may prefer to use [`Self::reordered_levels_per_char()`] instead
/// to avoid non-byte indices.
///
/// For an all-in-one reordering solution, consider using [`Self::reorder_visual()`].
///
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn reordered_levels_per_char(
&self,
para: &ParagraphInfo,
line: Range<usize>,
) -> Vec<Level> {
let levels = self.reordered_levels(para, line);
self.text.char_indices().map(|(i, _)| levels[i]).collect()
}
/// Re-order a line based on resolved levels and return the line in display order.
///
/// This does not apply [Rule L3] or [Rule L4] around combining characters or mirroring.
///
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn reorder_line(&self, para: &ParagraphInfo, line: Range<usize>) -> Cow<'text, [u16]> {
if !level::has_rtl(&self.levels[line.clone()]) {
return self.text[line].into();
}
let (levels, runs) = self.visual_runs(para, line.clone());
reorder_line(self.text, line, levels, runs)
}
/// Reorders pre-calculated levels of a sequence of characters.
///
/// NOTE: This is a convenience method that does not use a `Paragraph` object. It is
/// intended to be used when an application has determined the levels of the objects (character sequences)
/// and just needs to have them reordered.
///
/// the index map will result in `indexMap[visualIndex]==logicalIndex`.
///
/// information about the actual text.
///
/// Furthermore, if `levels` is an array that is aligned with code units, bytes within a codepoint may be
/// reversed. You may need to fix up the map to deal with this. Alternatively, only pass in arrays where each `Level`
/// is for a single code point.
///
///
/// # # Example
/// ```
/// use unicode_bidi::BidiInfo;
/// use unicode_bidi::Level;
///
/// let l0 = Level::from(0);
/// let l1 = Level::from(1);
/// let l2 = Level::from(2);
///
/// let levels = vec![l0, l0, l0, l0];
/// let index_map = BidiInfo::reorder_visual(&levels);
/// assert_eq!(levels.len(), index_map.len());
/// assert_eq!(index_map, [0, 1, 2, 3]);
///
/// let levels: Vec<Level> = vec![l0, l0, l0, l1, l1, l1, l2, l2];
/// let index_map = BidiInfo::reorder_visual(&levels);
/// assert_eq!(levels.len(), index_map.len());
/// assert_eq!(index_map, [0, 1, 2, 6, 7, 5, 4, 3]);
/// ```
#[cfg_attr(feature = "flame_it", flamer::flame)]
#[inline]
pub fn reorder_visual(levels: &[Level]) -> Vec<usize> {
reorder_visual(levels)
}
/// Find the level runs within a line and return them in visual order.
///
/// `line` is a range of bytes indices within `levels`.
///
/// The first return value is a vector of levels used by the reordering algorithm,
/// i.e. the result of [Rule L1]. The second return value is a vector of level runs,
/// the result of [Rule L2], showing the visual order that each level run (a run of text with the
/// same level) should be displayed. Within each run, the display order can be checked
/// against the Level vector.
///
/// This does not handle [Rule L3] (combining characters) or [Rule L4] (mirroring),
/// as that should be handled by the engine using this API.
///
/// Conceptually, this is the same as running [`Self::reordered_levels()`] followed by
/// [`Self::reorder_visual()`], however it returns the result as a list of level runs instead
/// of producing a level map, since one may wish to deal with the fact that this is operating on
/// byte rather than character indices.
///
///
#[cfg_attr(feature = "flame_it", flamer::flame)]
#[inline]
pub fn visual_runs(
&self,
para: &ParagraphInfo,
line: Range<usize>,
) -> (Vec<Level>, Vec<LevelRun>) {
let levels = self.reordered_levels(para, line.clone());
visual_runs_for_line(levels, &line)
}
/// If processed text has any computed RTL levels
///
/// This information is usually used to skip re-ordering of text when no RTL level is present
#[inline]
pub fn has_rtl(&self) -> bool {
level::has_rtl(&self.levels)
}
}
/// Bidi information of text treated as a single paragraph.
///
/// The `original_classes` and `levels` vectors are indexed by code unit offsets into the text. If a
/// character is multiple code units wide, then its class and level will appear multiple times in these
/// vectors.
#[derive(Debug, PartialEq)]
pub struct ParagraphBidiInfo<'text> {
/// The text
pub text: &'text [u16],
/// The BidiClass of the character at each byte in the text.
pub original_classes: Vec<BidiClass>,
/// The directional embedding level of each byte in the text.
pub levels: Vec<Level>,
/// The paragraph embedding level.
pub paragraph_level: Level,
/// Whether the paragraph is purely LTR.
pub is_pure_ltr: bool,
}
impl<'text> ParagraphBidiInfo<'text> {
/// Determine the bidi embedding level.
///
///
/// The `hardcoded-data` Cargo feature (enabled by default) must be enabled to use this.
///
/// TODO: In early steps, check for special cases that allow later steps to be skipped. like
/// text that is entirely LTR. See the `nsBidi` class from Gecko for comparison.
///
/// TODO: Support auto-RTL base direction
#[cfg_attr(feature = "flame_it", flamer::flame)]
#[cfg(feature = "hardcoded-data")]
#[inline]
pub fn new(text: &[u16], default_para_level: Option<Level>) -> ParagraphBidiInfo<'_> {
Self::new_with_data_source(&HardcodedBidiData, text, default_para_level)
}
/// Determine the bidi embedding level, with a custom [`BidiDataSource`]
/// for Bidi data. If you just wish to use the hardcoded Bidi data, please use [`BidiInfo::new()`]
/// instead (enabled with tbe default `hardcoded-data` Cargo feature).
///
/// (This is the single-paragraph equivalent of BidiInfo::new_with_data_source,
/// and should be kept in sync with it.
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn new_with_data_source<'a, D: BidiDataSource>(
data_source: &D,
text: &'a [u16],
default_para_level: Option<Level>,
) -> ParagraphBidiInfo<'a> {
// Here we could create a ParagraphInitialInfo struct to parallel the one
// used by BidiInfo, but there doesn't seem any compelling reason for it.
let (original_classes, paragraph_level, is_pure_ltr, has_isolate_controls) =
compute_initial_info(data_source, text, default_para_level, None);
let mut levels = Vec::<Level>::with_capacity(text.len());
let mut processing_classes = original_classes.clone();
let para_info = ParagraphInfo {
range: Range {
start: 0,
end: text.len(),
},
level: paragraph_level,
};
compute_bidi_info_for_para(
data_source,
¶_info,
is_pure_ltr,
has_isolate_controls,
text,
&original_classes,
&mut processing_classes,
&mut levels,
);
ParagraphBidiInfo {
text,
original_classes,
levels,
paragraph_level,
is_pure_ltr,
}
}
/// Produce the levels for this paragraph as needed for reordering, one level per *code unit*
/// in the paragraph. The returned vector includes code units that are not included
/// in the `line`, but will not adjust them.
///
/// See BidiInfo::reordered_levels for details.
///
/// (This should be kept in sync with BidiInfo::reordered_levels.)
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn reordered_levels(&self, line: Range<usize>) -> Vec<Level> {
assert!(line.start <= self.levels.len());
assert!(line.end <= self.levels.len());
let mut levels = self.levels.clone();
let line_classes = &self.original_classes[line.clone()];
let line_levels = &mut levels[line.clone()];
reorder_levels(
line_classes,
line_levels,
self.text.subrange(line),
self.paragraph_level,
);
levels
}
/// Produce the levels for this paragraph as needed for reordering, one level per *character*
/// in the paragraph. The returned vector includes characters that are not included
/// in the `line`, but will not adjust them.
///
/// See BidiInfo::reordered_levels_per_char for details.
///
/// (This should be kept in sync with BidiInfo::reordered_levels_per_char.)
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn reordered_levels_per_char(&self, line: Range<usize>) -> Vec<Level> {
let levels = self.reordered_levels(line);
self.text.char_indices().map(|(i, _)| levels[i]).collect()
}
/// Re-order a line based on resolved levels and return the line in display order.
///
/// See BidiInfo::reorder_line for details.
///
/// (This should be kept in sync with BidiInfo::reorder_line.)
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn reorder_line(&self, line: Range<usize>) -> Cow<'text, [u16]> {
if !level::has_rtl(&self.levels[line.clone()]) {
return self.text[line].into();
}
let (levels, runs) = self.visual_runs(line.clone());
reorder_line(self.text, line, levels, runs)
}
/// Reorders pre-calculated levels of a sequence of characters.
///
/// See BidiInfo::reorder_visual for details.
#[cfg_attr(feature = "flame_it", flamer::flame)]
#[inline]
pub fn reorder_visual(levels: &[Level]) -> Vec<usize> {
reorder_visual(levels)
}
/// Find the level runs within a line and return them in visual order.
///
/// `line` is a range of code-unit indices within `levels`.
///
/// See `BidiInfo::visual_runs` for details.
///
/// (This should be kept in sync with BidiInfo::visual_runs.)
#[cfg_attr(feature = "flame_it", flamer::flame)]
#[inline]
pub fn visual_runs(&self, line: Range<usize>) -> (Vec<Level>, Vec<LevelRun>) {
let levels = self.reordered_levels(line.clone());
visual_runs_for_line(levels, &line)
}
/// If processed text has any computed RTL levels
///
/// This information is usually used to skip re-ordering of text when no RTL level is present
#[inline]
pub fn has_rtl(&self) -> bool {
!self.is_pure_ltr
}
/// Return the paragraph's Direction (Ltr, Rtl, or Mixed) based on its levels.
#[inline]
pub fn direction(&self) -> Direction {
para_direction(&self.levels)
}
}
/// Return a line of the text in display order based on resolved levels.
///
/// `text` the full text passed to the `BidiInfo` or `ParagraphBidiInfo` for analysis
/// `line` a range of byte indices within `text` corresponding to one line
/// `levels` array of `Level` values, with `line`'s levels reordered into visual order
/// `runs` array of `LevelRun`s in visual order
///
/// (`levels` and `runs` are the result of calling `BidiInfo::visual_runs()` or
/// `ParagraphBidiInfo::visual_runs()` for the line of interest.)
///
/// Returns: the reordered text of the line.
///
/// This does not apply [Rule L3] or [Rule L4] around combining characters or mirroring.
///
fn reorder_line(
text: &[u16],
line: Range<usize>,
levels: Vec<Level>,
runs: Vec<LevelRun>,
) -> Cow<'_, [u16]> {
// If all isolating run sequences are LTR, no reordering is needed
if runs.iter().all(|run| levels[run.start].is_ltr()) {
return text[line].into();
}
let mut result = Vec::<u16>::with_capacity(line.len());
for run in runs {
if levels[run.start].is_rtl() {
let mut buf = [0; 2];
for c in text[run].chars().rev() {
result.extend(c.encode_utf16(&mut buf).iter());
}
} else {
result.extend(text[run].iter());
}
}
result.into()
}
/// Contains a reference of `BidiInfo` and one of its `paragraphs`.
/// And it supports all operation in the `Paragraph` that needs also its
/// `BidiInfo` such as `direction`.
#[derive(Debug)]
pub struct Paragraph<'a, 'text> {
pub info: &'a BidiInfo<'text>,
pub para: &'a ParagraphInfo,
}
impl<'a, 'text> Paragraph<'a, 'text> {
#[inline]
pub fn new(info: &'a BidiInfo<'text>, para: &'a ParagraphInfo) -> Paragraph<'a, 'text> {
Paragraph { info, para }
}
/// Returns if the paragraph is Left direction, right direction or mixed.
#[inline]
pub fn direction(&self) -> Direction {
para_direction(&self.info.levels[self.para.range.clone()])
}
/// Returns the `Level` of a certain character in the paragraph.
#[inline]
pub fn level_at(&self, pos: usize) -> Level {
let actual_position = self.para.range.start + pos;
self.info.levels[actual_position]
}
}
/// Implementation of TextSource for UTF-16 text in a [u16] array.
/// Note that there could be unpaired surrogates present!
// Convenience functions to check whether a UTF16 code unit is a surrogate.
#[inline]
fn is_high_surrogate(code: u16) -> bool {
(code & 0xFC00) == 0xD800
}
#[inline]
fn is_low_surrogate(code: u16) -> bool {
(code & 0xFC00) == 0xDC00
}
impl<'text> TextSource<'text> for [u16] {
type CharIter = Utf16CharIter<'text>;
type CharIndexIter = Utf16CharIndexIter<'text>;
type IndexLenIter = Utf16IndexLenIter<'text>;
#[inline]
fn len(&self) -> usize {
(self as &[u16]).len()
}
fn char_at(&self, index: usize) -> Option<(char, usize)> {
if index >= self.len() {
return None;
}
// Get the indicated code unit and try simply converting it to a char;
// this will fail if it is half of a surrogate pair.
let c = self[index];
if let Some(ch) = char::from_u32(c.into()) {
return Some((ch, 1));
}
// If it's a low surrogate, and was immediately preceded by a high surrogate,
// then we're in the middle of a (valid) character, and should return None.
if is_low_surrogate(c) && index > 0 && is_high_surrogate(self[index - 1]) {
return None;
}
// Otherwise, try to decode, returning REPLACEMENT_CHARACTER for errors.
if let Some(ch) = char::decode_utf16(self[index..].iter().cloned()).next() {
if let Ok(ch) = ch {
// This must be a surrogate pair, otherwise char::from_u32() above should
// have succeeded!
debug_assert!(ch.len_utf16() == 2, "BMP should have already been handled");
return Some((ch, ch.len_utf16()));
}
} else {
debug_assert!(
false,
"Why did decode_utf16 return None when we're not at the end?"
);
return None;
}
// Failed to decode UTF-16: we must have encountered an unpaired surrogate.
// Return REPLACEMENT_CHARACTER (not None), to continue processing the following text
// and keep indexing correct.
Some((char::REPLACEMENT_CHARACTER, 1))
}
#[inline]
fn subrange(&self, range: Range<usize>) -> &Self {
&(self as &[u16])[range]
}
#[inline]
fn chars(&'text self) -> Self::CharIter {
Utf16CharIter::new(self)
}
#[inline]
fn char_indices(&'text self) -> Self::CharIndexIter {
Utf16CharIndexIter::new(self)
}
#[inline]
fn indices_lengths(&'text self) -> Self::IndexLenIter {
Utf16IndexLenIter::new(self)
}
#[inline]
fn char_len(ch: char) -> usize {
ch.len_utf16()
}
}
/// Iterator over UTF-16 text in a [u16] slice, returning (index, char_len) tuple.
#[derive(Debug)]
pub struct Utf16IndexLenIter<'text> {
text: &'text [u16],
cur_pos: usize,
}
impl<'text> Utf16IndexLenIter<'text> {
#[inline]
pub fn new(text: &'text [u16]) -> Self {
Utf16IndexLenIter { text, cur_pos: 0 }
}
}
impl Iterator for Utf16IndexLenIter<'_> {
type Item = (usize, usize);
#[inline]
fn next(&mut self) -> Option<Self::Item> {
if let Some((_, char_len)) = self.text.char_at(self.cur_pos) {
let result = (self.cur_pos, char_len);
self.cur_pos += char_len;
return Some(result);
}
None
}
}
/// Iterator over UTF-16 text in a [u16] slice, returning (index, char) tuple.
#[derive(Debug)]
pub struct Utf16CharIndexIter<'text> {
text: &'text [u16],
cur_pos: usize,
}
impl<'text> Utf16CharIndexIter<'text> {
pub fn new(text: &'text [u16]) -> Self {
Utf16CharIndexIter { text, cur_pos: 0 }
}
}
impl Iterator for Utf16CharIndexIter<'_> {
type Item = (usize, char);
fn next(&mut self) -> Option<Self::Item> {
if let Some((ch, char_len)) = self.text.char_at(self.cur_pos) {
let result = (self.cur_pos, ch);
self.cur_pos += char_len;
return Some(result);
}
None
}
}
/// Iterator over UTF-16 text in a [u16] slice, returning Unicode chars.
/// (Unlike the other iterators above, this also supports reverse iteration.)
#[derive(Debug)]
pub struct Utf16CharIter<'text> {
text: &'text [u16],
cur_pos: usize,
end_pos: usize,
}
impl<'text> Utf16CharIter<'text> {
pub fn new(text: &'text [u16]) -> Self {
Utf16CharIter {
text,
cur_pos: 0,
end_pos: text.len(),
}
}
}
impl Iterator for Utf16CharIter<'_> {
type Item = char;
fn next(&mut self) -> Option<Self::Item> {
if let Some((ch, char_len)) = self.text.char_at(self.cur_pos) {
self.cur_pos += char_len;
return Some(ch);
}
None
}
}
impl DoubleEndedIterator for Utf16CharIter<'_> {
fn next_back(&mut self) -> Option<Self::Item> {
if self.end_pos <= self.cur_pos {
return None;
}
self.end_pos -= 1;
if let Some(ch) = char::from_u32(self.text[self.end_pos] as u32) {
return Some(ch);
}
if self.end_pos > self.cur_pos {
if let Some((ch, char_len)) = self.text.char_at(self.end_pos - 1) {
if char_len == 2 {
self.end_pos -= 1;
return Some(ch);
}
}
}
Some(char::REPLACEMENT_CHARACTER)
}
}