这是为了开发大型程序，分治crate用的。

目录结构如下：

 

一，根cargo.toml内容

[workspace]

members = [
    "adder",
    "add-one",
    
]

二，adder里的cargo.toml内容

[package]
name = "adder"
version = "0.1.0"
authors = ["test <test@qq.com>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
add-one = { path = "../add-one" }

三，main.rs内容

use add_one;

fn main() {
    let num = 10; 
    println!("Hello, world! {} plus one is {}!", num, add_one::add_one(num));
}

四，Lib.rs内容

pub fn add_one(x: i32) -> i32 {
    x + 1
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_works() {
        assert_eq!(3, add_one(2));
    }
}