如何用 ndarray 初始化一个常量矩阵? [英] How to init a constant matrix with ndarray?

问题描述

我想在 ndarray 中有一个矩阵作为其他模块可用的常量.不幸的是，构造函数本身并不是一个常数函数.有没有办法绕过这个限制?

I would like to have a matrix in ndarray as a constant available for other modules. Unfortunately, the construction function itself is not a constant function. Is there any way around that restriction?

代码:

extern crate ndarray;

use ndarray::prelude::*;

const foo: Array2<f32> = arr2(&[
    [1.26, 0.09], [0.79, 0.92]
]);

fn main() {
    println!("{}", foo);
}

错误:

error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
 --> src\main.rs:5:26
  |
5 |   const foo: Array2<f32> = arr2(&[
  |  __________________________^
6 | |     [1.26, 0.09], [0.79, 0.92]
7 | | ]);
  | |__^

推荐答案

您可以声明一个不可变的静态变量而不是 const(因为 const 仅在编译时计算)，然后使用 惰性静态，即

You can declare a immutable static variable instead of a const (since consts are compile time evaluated only), and then use lazy-static, which is

用于在 Rust 中声明延迟评估的静态的宏.

A macro for declaring lazily evaluated statics in Rust.

运行您的函数并设置静态变量.

to run your function and set the static variable.

示例:游乐场

#[macro_use]
extern crate lazy_static;

pub mod a_mod {
    lazy_static! {
        pub static ref FOO: ::std::time::SystemTime = ::std::time::SystemTime::now();
    }
}

fn main() {
    println!("{:?}", *a_mod::foo);
}

它会要求你在使用它之前取消引用它.

It would require you to deref the variable before you use it though.

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