问题描述
我有一个包含坐标 vec 的结构 (Lines)。
我正在尝试将非重叠子切片上的非消耗可变迭代器实现为 &mut [Coordinate]。每个子切片将代表存储在 Lines 中的 1 行。
-edit：此外，可以在不移动顶点的情况下重新排序索引列表。因此，不能假设顶点中的线与索引的顺序相同。
该实现适用于不可变迭代器（与下面的实现相同，但没有 muts）
use std::ops::{Index,IndexMut};
#[derive(Debug)]
pub struct Coordinate {
x: u32,y: u32,}
/// SOA containing multiple line geometries
/// All coordinates of all the lines are stored contiguously in vertices
/// start_indices & end_indices both contain 1 entry for every geometry
#[derive(Debug)]
struct Lines {
vertices: Vec<Coordinate>,start_indices: Vec<usize>,end_indices: Vec<usize>,}
impl Lines {
pub fn len(&self) -> usize {
self.start_indices.len()
}
fn iter_mut(&mut self) -> LinesIterMut {
LinesIterMut {
lines: self,next_index: 0,}
}
}
impl Index<usize> for Lines {
type Output = [Coordinate];
fn index(&self,index: usize) -> &Self::Output {
&self.vertices[self.start_indices[index]..self.end_indices[index]]
}
}
impl IndexMut<usize> for Lines {
fn index_mut(&mut self,index: usize) -> &mut Self::Output {
&mut self.vertices[self.start_indices[index]..self.end_indices[index]]
}
}
pub struct LinesIterMut<'a> {
lines: &'a mut Lines,next_index: usize,}
impl<'a> Iterator for LinesIterMut<'a> {
type Item = &'a mut [Coordinate];
fn next(&mut self) -> Option<Self::Item> {
if self.next_index < self.lines.len() {
let current_index = self.next_index;
self.next_index += 1;
Some(&mut self.lines[current_index])
} else {
None
}
}
}
fn main() {
let mut my_lines = Lines {
vertices: vec![
Coordinate {
x: 1,y: 2,},Coordinate {
x: 4,y: 5,],start_indices: vec![0],end_indices: vec![2],};
for line in my_lines.iter_mut() {
line[0].y = 33;
println!("=> {:?}",line);
}
}
我收到以下生命周期错误：
error[E0495]: cannot infer an appropriate lifetime for lifetime parameter in function call due to conflicting requirements
--> src/main.rs:54:23
|
54 | Some(&mut self.lines[current_index])
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: first,the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 50:5...
--> src/main.rs:50:5
|
50 | fn next(&mut self) -> Option<Self::Item> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...so that reference does not outlive borrowed content
--> src/main.rs:54:23
|
54 | Some(&mut self.lines[current_index])
| ^^^^^^^^^^
note: but,the lifetime must be valid for the lifetime `'a` as defined on the impl at 47:6...
--> src/main.rs:47:6
|
47 | impl<'a> Iterator for LinesIterMut<'a> {
| ^^
note: ...so that the types are compatible
--> src/main.rs:50:46
|
50 | fn next(&mut self) -> Option<Self::Item> {
| ______________________________________________^
51 | | if self.next_index < self.lines.len() {
52 | | let current_index = self.next_index;
53 | | self.next_index += 1;
... |
57 | | }
58 | | }
| |_____^
= note: expected `Iterator`
found `Iterator`
如何告诉编译器引用的生命周期与 Lines 相关？
-edit：使用@kmdreko 提供的链接：https://stackoverflow.com/a/60072822/13138916 我写了这个。 它有效，但这安全吗？我怎么知道？
pub struct LinesIterMut<'a> {
lines: &'a mut Lines,}
impl<'a> Iterator for LinesIterMut<'a> {
type Item = &'a mut [Coordinate];
fn next(&mut self) -> Option<Self::Item> {
if self.next_index < self.lines.len() {
let current_index = self.next_index;
self.next_index += 1;
Some(unsafe { std::mem::transmute(&mut self.lines[current_index]) }) // <<--- Only changed this line
} else {
None
}
}
}
解决方法
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