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//! Source code offsets.
//!
//! The [`Emitter`](crate::Emitter) is generic over an [`Offset`].
//! This library comes with two Offset implementations:
//!
//! * [`NoopOffset`] for when you don't want to track source offsets
//! * `usize` for when you do want to track source offsets
//!
//! To use the latter your reader however has to implement [`Position<usize>`].
//! You can easily use any existing reader by wrapping it in the [`PosTrackingReader`] struct
//! which implements the [`Position<usize>`] trait and takes care of tracking the current position.
use std::fmt::Debug;
use std::ops::{Add, AddAssign, Sub};
use crate::reader::{IntoReader, Reader};
/// A byte offset in the source.
pub trait Offset:
Default
+ Copy
+ Eq
+ Ord
+ Add<usize, Output = Self>
+ Sub<usize, Output = Self>
+ AddAssign<usize>
+ Debug
{
}
impl Offset for usize {}
impl Offset for NoopOffset {}
/// A zero-sized no-op implementation of [`Offset`] (for when you don't want to track offsets).
#[derive(Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
pub struct NoopOffset;
/// A trait to be implemented by readers that track their own position.
pub trait Position<T> {
/// Returns the byte index of the current position.
fn position(&self) -> T;
}
impl<R: Reader> Position<NoopOffset> for R {
fn position(&self) -> NoopOffset {
NoopOffset
}
}
/// Wraps a [`Reader`] so that it implements [`Position<usize>`].
pub struct PosTrackingReader<R> {
/// The wrapped reader.
reader: R,
/// The current position.
position: usize,
}
impl<R> PosTrackingReader<R> {
/// Wraps the given [`Reader`] so that it implements [`Position<usize>`] with the position starting from 0.
pub fn new<'a>(into_reader: impl IntoReader<'a, Reader = R>) -> Self {
Self {
reader: into_reader.into_reader(),
position: 0,
}
}
}
impl<R> Position<usize> for PosTrackingReader<R> {
fn position(&self) -> usize {
self.position
}
}
impl Add<usize> for NoopOffset {
type Output = Self;
fn add(self, _rhs: usize) -> NoopOffset {
self
}
}
impl Sub<usize> for NoopOffset {
type Output = Self;
fn sub(self, _rhs: usize) -> NoopOffset {
self
}
}
impl AddAssign<usize> for NoopOffset {
fn add_assign(&mut self, _rhs: usize) {}
}
impl<R: Reader> Reader for PosTrackingReader<R> {
type Error = R::Error;
fn read_char(&mut self) -> Result<Option<char>, Self::Error> {
match self.reader.read_char()? {
Some(char) => {
self.position += char.len_utf8();
Ok(Some(char))
}
None => Ok(None),
}
}
fn try_read_string(&mut self, s: &str, case_sensitive: bool) -> Result<bool, Self::Error> {
match self.reader.try_read_string(s, case_sensitive)? {
true => {
self.position += s.len();
Ok(true)
}
false => Ok(false),
}
}
}
|
