实现 rust 结构时如何处理生命周期？答案

【问题标题】：How do I deal with lifetimes when implementing rust structs?实现 rust 结构时如何处理生命周期？
【发布时间】：2020-02-21 16:43:17
【问题描述】：

所以，我一直在浏览 Handmade Hero 视频系列，我认为将代码转换为 rust 会是一个有趣的练习。但是，我以前从来没有真正处理过生命周期，现在我得到了与它们相关的编译错误。我目前有以下代码：

struct TextureData<'a> {
    texture: Texture<'a>,
    width: usize,
    height: usize,
    bytes_per_pixel: usize,
    pixels: Vec<u8>
}

impl TextureData<'_> {
    fn new(texture: Texture, width: usize, height: usize) -> Self {
        TextureData { texture, width, height, bytes_per_pixel: PIXEL_BYTES, pixels: Vec::new() }
    }

    fn fill_texture(&mut self) {
        let size = self.width * self.height * self.bytes_per_pixel;
        let mut pixels: Vec<u8> = Vec::with_capacity(size);
        for i in 0..(self.width * self.height){
            let x = i / self.width;
            let y = i % self.height;
            pixels.push((x % 0xff) as u8);
            pixels.push((y % 0xff) as u8);
            pixels.push(0);
            pixels.push(0);
        }

        self.pixels = pixels;
    }

    fn update(&mut self) {
        let pitch = self.width * self.bytes_per_pixel;
        self.texture.update(None, &self.pixels, pitch);
    }
}

我收到以下反馈：

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
  --> src/main.rs:21:2
   |
21 |     TextureData { texture, width, height, bytes_per_pixel: PIXEL_BYTES, pixels: Vec::new() }
   |     ^^^^^^^^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 20:5...
  --> src/main.rs:20:5
   |
20 | /     fn new(texture: Texture, width: usize, height: usize) -> Self {
21 | |     TextureData { texture, width, height, bytes_per_pixel: PIXEL_BYTES, pixels: Vec::new() }
22 | |     }
   | |_____^
note: ...so that the expression is assignable
  --> src/main.rs:21:16
   |
21 |     TextureData { texture, width, height, bytes_per_pixel: PIXEL_BYTES, pixels: Vec::new() }
   |                   ^^^^^^^
   = note: expected  `sdl2::render::Texture<'_>`
              found  `sdl2::render::Texture<'_>`
note: but, the lifetime must be valid for the lifetime `'_` as defined on the impl at 19:18...
  --> src/main.rs:19:18
   |
19 | impl TextureData<'_> {
   |                  ^^
note: ...so that the expression is assignable
  --> src/main.rs:21:2
   |
21 |     TextureData { texture, width, height, bytes_per_pixel: PIXEL_BYTES, pixels: Vec::new() }
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: expected  `TextureData<'_>`
              found  `TextureData<'_>`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0495`.

当然，我已经阅读了 E0495 的文档，但我不知道它在这种情况下如何应用。

【问题讨论】：

标签： rust lifetime

【解决方案1】：

您需要像声明 TextureData 结构时所做的那样重复它：

impl<'a> TextureData<'a> {
    fn new(texture: Texture<'a>, width: usize, height: usize) -> Self {
        ...
    }

    ...
}

注意添加的 3 <'a>。不一定是'a，在这三个地方也可以是'b。

或者，如果你想使用“匿名生命周期”的形式，那么你需要这样写。

impl TextureData<'_> {
    fn new(texture: Texture<'_>, width: usize, height: usize) -> TextureData<'_> {
        ...
    }

    ...
}

【讨论】：