如何在编译时创建静态字符串 [英] How to create a static string at compile time

问题描述

我想创建一个由重复字符序列组成的长 &'static str，例如abcabcabc...

I want to create a long &'static str made of repeating sequences of chars, e.g. abcabcabc...

在 Rust 中有没有办法通过表达式来做到这一点，例如像 Python 中的 long_str = 1000 * "abc" 之类的东西，还是我必须在 Python 中生成它并将其复制/粘贴到 Rust 代码中?

Is there a way in Rust to do this via an expression, e.g. something like long_str = 1000 * "abc" in Python, or do I have to generate it in Python and copy/paste it in the Rust code?

推荐答案

你不能在稳定的 Rust 中做这样的事情.您的 1000 * abc" 示例不在编译时"运行；在 Python 中，据我了解 Python.

You cannot do such a thing in stable Rust. Your example of 1000 * "abc" is not run at "compile time" in Python either, as far as I understand Python.

如果必须是静态的，您可以使用 货物构建脚本.这是一些 Rust 代码，可以在实际编译代码之前做很多事情.具体来说，您可以编写一个包含字符串的源文件，然后使用 include_str! 将其放入您的板条箱:

If it has to be static, you could use a Cargo build script. This is a bit of Rust code that can do lots of things before your code is actually compiled. Specifically, you could write a source file out that has your string and then use include_str! to bring it into your crate:

build.rs

use std::{
    env, error::Error, fs::File, io::{BufWriter, Write}, path::Path,
};

fn main() -> Result<(), Box<Error>> {
    let out_dir = env::var("OUT_DIR")?;
    let dest_path = Path::new(&out_dir).join("long_string.txt");
    let mut f = BufWriter::new(File::create(&dest_path)?);

    let long_string = "abc".repeat(100);
    write!(f, "{}", long_string)?;

    Ok(())
}

lib.rs

static LONG_STRING: &'static str = include_str!(concat!(env!("OUT_DIR"), "/long_string.txt"));

延迟初始化

您可以创建一个 once_cell 或 lazy_static 将在运行时创建字符串的值，但只能创建一次.

Lazy initialization

You could create a once_cell or lazy_static value that would create your string at runtime, but only once.

use once_cell::sync::Lazy; // 1.5.2

static LONG_STR: Lazy<String> = Lazy::new(|| "abc".repeat(5000));

另见:

• 如何在 Rust 中创建安全的静态单例?
• 如何创建全局可变单例?

在某些时候，RFC 911 将全面实施.再加上一些额外的 RFC，每一个都增加了新的功能，将使您能够编写如下内容:

At some point, RFC 911 will be fully implemented. This, plus a handful of additional RFCs, each adding new functionality, will allow you to be able to write something like:

// Does not work yet!
static LONG_STR: String = "abc".repeat(1000);

这篇关于如何在编译时创建静态字符串的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！