英文:
implement Default for a templated struct where the only difference is the templated variable
问题
在定义了一个具有长度模板的矩阵之后，以便我可以更轻松地控制大小：
pub struct SquareMatrix<const length: usize> {
data: [[f32; length]; length],
}
我为该矩阵定义了默认函数：
impl Default for SquareMatrix<2> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; 2]; 2],
}
}
}
impl Default for SquareMatrix<3> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; 3]; 3],
}
}
}
impl Default for SquareMatrix<4> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; 4]; 4],
}
}
}
这看起来不够优雅，因为它们唯一的区别是模板的长度。但是，当我去掉length并且只定义一个有模板的函数时：
impl Default for SquareMatrix<length> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; length]; length],
}
}
}
出现错误提示：length not found in this scope
是否有一种方法可以为模板结构定义一个模板函数？
英文:
After defining a matrix where the length templated so I can control the size easier:
pub struct SquareMatrix<const length: usize> {
data: [[f32; length]; length],
}
I define default functions for the matrix:
impl Default for SquareMatrix<2> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; 2];2],
}
}
}
impl Default for SquareMatrix<3> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; 3];3],
}
}
}
impl Default for SquareMatrix<4> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; 4];4],
}
}
}
It does not look elegant as the only difference of them is the length which is templated. But when I take out the length and define only 1 templated function:
impl Default for SquareMatrix<length> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; length]; length],
}
}
}
Error prompt: length not found in this scope
Is there a way to define a templated function for templated struct?
答案1
得分: 3
你已经很接近了，你只需要在Default实现中定义泛型参数：
#[derive(Debug)]
pub struct SquareMatrix<const LENGTH: usize> {
data: [[f32; LENGTH]; LENGTH],
}
impl<const LENGTH: usize> Default for SquareMatrix<LENGTH> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; LENGTH]; LENGTH],
};
}
}
fn main() {
let matrix: SquareMatrix<2> = Default::default();
println!("{:?}", matrix);
}
SquareMatrix { data: [[0.0, 0.0], [0.0, 0.0]] }
还有一点小问题：const泛型应该使用全大写字母表示。
英文:
You are close, you just need to define the generic in the Default implementation:
#[derive(Debug)]
pub struct SquareMatrix<const LENGTH: usize> {
data: [[f32; LENGTH]; LENGTH],
}
impl<const LENGTH: usize> Default for SquareMatrix<LENGTH> {
fn default() -> Self {
return SquareMatrix {
data: [[0.0; LENGTH]; LENGTH],
};
}
}
fn main() {
let matrix: SquareMatrix<2> = Default::default();
println!("{:?}", matrix);
}
SquareMatrix { data: [[0.0, 0.0], [0.0, 0.0]] }
Also, minor nitpick: const generics should be written in all caps.
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