重构模块会从编译器创建不同类型的请求？

Question

为什么我在重构此 example code to use a wrapper around the resize 图像库时收到不同类型的编译器请求。

基本上调整大小似乎总是 u16 输出，所以为什么我的更改要求 u8 而原始代码从来不需要此转换？

extern crate resize;

use resize::Type;
use resize::Pixel;

pub struct Resize{
    w1:usize,
    h1:usize,
    w2:usize,
    h2:usize,
    src: Vec<u16>,
}

impl Resize {
    pub fn new(
        ow:usize, 
        oh:usize, 
        dw:usize, 
        dh:usize,
        inc: Vec<u16>
    ) -> Resize {
        Resize {
            w1:ow,
            h1:oh,
            w2:dw,
            h2:dh,
            src:inc,
        }
    }

    pub fn run(&self) -> Vec<u16> {
        let mut dst = vec![0;self.w2*self.h2];
        resize::resize(
            self.w1, 
            self.h1, 
            self.w2, 
            self.h2, 
            Pixel::RGBA64, 
            Type::Lanczos3, 
            self.src.as_slice(), 
            &mut dst,
        );
        dst
    }
}

编译错误信息

error[E0308]: mismatched types
  --> src/main.rs:24:45
   |
24 |     let image = Resize::new(w1, h1, w2, h2, src);
   |                                             ^^^ expected u16, found u8
   |
   = note: expected type `std::vec::Vec<u16>`
              found type `std::vec::Vec<u8>`
   = help: here are some functions which might fulfill your needs:
           - .to_vec()

error[E0308]: mismatched types
  --> src/main.rs:30:54
   |
30 |     encoder.write_header().unwrap().write_image_data(dst).unwrap();
   |                                                      ^^^ expected u8, found u16
   |
   = note: expected type `&[u8]`
              found type `&[u16]`

Answer 1

TL;DR：src 变量的预期类型是 Vec<u16>，但由于类型推断，它被设置为 Vec<u8>。

变量 src 在行中赋值：

let mut src = vec![0;info.buffer_size()];

稍后通过调用

推断类型为Vec<u8>

reader.next_frame(&mut src).unwrap();

或

resize::resize(w1, h1, w2, h2, Gray8, Triangle, &src, &mut dst);

因为这些函数需要类型 &mut [u8]，而不是 &mut [u16]。

如果我们在分配 src 时显式设置预期类型 Vec<u16>:

let mut src: Vec<u16> = vec![0; info.buffer_size()];

现在调用 next_frame() 和 resize() 将失败，因为类型不匹配，但编译器会为我们提供更好的提示，告诉我们哪里出了问题以及我们可以采取什么措施。

error[E0308]: mismatched types
  --> src/main.rs:65:23
   |
65 |     reader.next_frame(&mut src).unwrap();
   |                       ^^^^^^^^ expected slice, found struct `std::vec::Vec`
   |
   = note: expected type `&mut [u8]`
              found type `&mut std::vec::Vec<u16>`
   = help: here are some functions which might fulfill your needs:
           - .as_mut_slice()

error[E0308]: mismatched types
  --> src/main.rs:74:53
   |
74 |     resize::resize(w1, h1, w2, h2, Gray8, Triangle, &src, &mut dst);
   |                                                     ^^^^ expected slice, found struct `std::vec::Vec`
   |
   = note: expected type `&[u8]`
              found type `&std::vec::Vec<u16>`
   = help: here are some functions which might fulfill your needs:
           - .as_slice()

重构模块会从编译器创建不同类型的请求？

Refactor to module creates different type request from compiler?

types

rust

image-resizing