boa_string 0.21.0

Boa is a Javascript lexer, parser and compiler written in Rust. Currently, it has support for some of the language.
Documentation 
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use std::iter::FusedIterator;

use crate::JsStr;

use super::JsStrVariant;

#[derive(Debug, Clone)]
enum IterInner<'a> {
    U8(std::iter::Copied<std::slice::Iter<'a, u8>>),
    U16(std::iter::Copied<std::slice::Iter<'a, u16>>),
}

/// Iterator over a [`JsStr`].
#[derive(Debug, Clone)]
pub struct Iter<'a> {
    inner: IterInner<'a>,
}

impl<'a> Iter<'a> {
    pub(crate) fn new(s: JsStr<'a>) -> Self {
        let inner = match s.variant() {
            JsStrVariant::Latin1(s) => IterInner::U8(s.iter().copied()),
            JsStrVariant::Utf16(s) => IterInner::U16(s.iter().copied()),
        };
        Iter { inner }
    }
}

impl Iterator for Iter<'_> {
    type Item = u16;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        match &mut self.inner {
            IterInner::U8(iter) => iter.map(u16::from).next(),
            IterInner::U16(iter) => iter.next(),
        }
    }
}

impl FusedIterator for Iter<'_> {}

impl ExactSizeIterator for Iter<'_> {
    #[inline]
    fn len(&self) -> usize {
        match &self.inner {
            IterInner::U8(v) => v.len(),
            IterInner::U16(v) => v.len(),
        }
    }
}

#[derive(Debug, Clone)]
enum WindowsInner<'a> {
    U8(std::slice::Windows<'a, u8>),
    U16(std::slice::Windows<'a, u16>),
}

/// An iterator over overlapping subslices of length size.
///
/// This struct is created by the `windows` method.
#[derive(Debug, Clone)]
pub struct Windows<'a> {
    inner: WindowsInner<'a>,
}

impl<'a> Windows<'a> {
    pub(crate) fn new(string: JsStr<'a>, size: usize) -> Self {
        let inner = match string.variant() {
            JsStrVariant::Latin1(v) => WindowsInner::U8(v.windows(size)),
            JsStrVariant::Utf16(v) => WindowsInner::U16(v.windows(size)),
        };
        Self { inner }
    }
}

impl<'a> Iterator for Windows<'a> {
    type Item = JsStr<'a>;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        match &mut self.inner {
            WindowsInner::U8(iter) => iter.next().map(JsStr::latin1),
            WindowsInner::U16(iter) => iter.next().map(JsStr::utf16),
        }
    }
}

impl FusedIterator for Windows<'_> {}

impl ExactSizeIterator for Windows<'_> {
    #[inline]
    fn len(&self) -> usize {
        match &self.inner {
            WindowsInner::U8(v) => v.len(),
            WindowsInner::U16(v) => v.len(),
        }
    }
}