Part 1: Make the tests compile

配置好之后尝试运行 cargo test，发现编译错误：

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error[E0433]: failed to resolve: use of undeclared crate or module `assert_cmd`
 --> tests\tests.rs:1:5
  |
1 | use assert_cmd::prelude::*;
  |     ^^^^^^^^^^ use of undeclared crate or module `assert_cmd`

显然是缺少相应的 crate，在 cargo.toml 里面加上。

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[dev-dependencies]
assert_cmd = "0.11.0"
predicates = "1.0.0"

dev-dependencies 和 dependencies 的区别可以看官方文档

再次运行 cargo test，发现编译错误：

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error[E0432]: unresolved import `kvs::KvStore`
 --> tests\tests.rs:2:5
  |
2 | use kvs::KvStore;
  |     ^^^^^^^^^^^^ no `KvStore` in the root

也就是还没有实现对应的接口，先在 kvs/src/lib.rs 中添加对应的接口，内容直接 panic!() 就行（也可以用 unimplemented!，不过有点麻烦）。

观察 tests.rs，根据里面的调用写对应的函数。

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pub struct KvStore {}

impl KvStore {
    pub fn new() -> Self {
        unimplemented!();
    }

    pub fn set(&mut self, _key: String, _value: String) {
        unimplemented!();
    }

    pub fn get(&self, _key: String) -> Option<String> {
        unimplemented!();
    }

    pub fn remove(&mut self, _key: String) {
        unimplemented!();
    }
}

然后 cargo test --no-run，发现可以通过编译。

Part 2: Accept command line arguments

使用 clap crate 进行参数解析。

参考 docs.rs 上的教程，首先 cargo add clap --features derive 启用功能，然后依次添加对应的 Subcommand：

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// src/lib.rs
use clap::{Parser, Subcommand};

#[derive(Parser)]
#[command(author, version, about, long_about = None)]
pub struct Args {
    #[command(subcommand)]
    pub command: Command,
}

#[derive(Subcommand)]
pub enum Command {
    Set { key: String, value: String },
    Get { key: String },
    Rm { key: String },
}
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// src/bin/kvs.rs
use clap::Parser;
use kvs::{Args, Command, KvStore};

fn main() {
    let mut store = KvStore::new();
    let args = Args::parse();
    match args.command {
        Command::Set { key, value } => {
            store.set(key, value);
        }
        Command::Get { key } => {
            store.get(key);
        }
        Command::Rm { key } => {
            store.remove(key);
        }
    }
}

然后使用 cargo test cli 进行测试。

Part 3: Cargo environment variables

在 cargo.toml 中设置 clap crate 的一些默认参数。一个简单例子：

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[package]
name = "kvs"
version = "0.1.0"
authors = ["MizukiCry <YuukaC@outlook.com>"]
description = "An in-memory key-value store for study."
edition = "2021"

Part 4: Store values in memory

实现 KvStore 的接口通过剩余测试，其实也就是套 HashMap：

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pub struct KvStore {
    store: HashMap<String, String>,
}

impl KvStore {
    pub fn new() -> Self {
        Self {
            store: HashMap::new(),
        }
    }

    pub fn set(&mut self, key: String, value: String) {
        self.store.insert(key, value);
    }

    pub fn get(&self, key: String) -> Option<String> {
        self.store.get(&key).cloned()
    }

    pub fn remove(&mut self, key: String) {
        self.store.remove(&key).unwrap();
    }
}

Part 5: Documentation

为 src/lib.rs 内所有内容加上注释。

顺便将解析参数的内容移到了 src/bin/kvs.rs 中，更加方便。

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// src/lib.rs
#![deny(missing_docs)]
//! `kvs` is a crate that privodes an in-memory key-value store.

use std::collections::HashMap;

/// An in-memory key-value store.
///
/// # Examples
///
/// ```rust
/// use kvs::KvStore;
///
/// let mut store = KvStore::new();
/// store.set(String::from("Ayumu"), String::from("Uehara"));
/// assert_eq!(Some(String::from("Uehara")), store.get(String::from("Ayumu")));
/// store.remove(String::from("Ayumu"));
/// assert_eq!(None, store.get(String::from("Ayumu")));
/// ```
pub struct KvStore {
    store: HashMap<String, String>,
}

impl KvStore {
    /// Returns a `KvStore` instance.
    pub fn new() -> Self {
        Self {
            store: HashMap::new(),
        }
    }

    /// Inserts a new key-value pair into the store.
    pub fn set(&mut self, key: String, value: String) {
        self.store.insert(key, value);
    }

    /// Query the value by the given key. Returns `None` if the key doesn't exist.
    pub fn get(&self, key: String) -> Option<String> {
        self.store.get(&key).cloned()
    }

    /// Remove a key in the store if exists.
    pub fn remove(&mut self, key: String) {
        self.store.remove(&key).unwrap();
    }
}
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// src/bin/kvs.rs
use clap::{Parser, Subcommand};
use kvs::KvStore;

#[derive(Parser)]
#[command(author, version, about, long_about = None)]
struct Args {
    #[command(subcommand)]
    command: Command,
}

#[derive(Subcommand)]
enum Command {
    Set { key: String, value: String },
    Get { key: String },
    Rm { key: String },
}

fn main() {
    let mut store = KvStore::new();
    let args = Args::parse();
    match args.command {
        Command::Set { key, value } => {
            store.set(key, value);
        }
        Command::Get { key } => {
            store.get(key);
        }
        Command::Rm { key } => {
            store.remove(key);
        }
    }
}

完成之后可以通过 cargo doc --open 查看文档，cargo test --doc 单独测试。

Part 6: Ensure good style with clippy and rustfmt

安装 clippy 和 rustfmt 工具：

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rustup component add clippy
rustup component add rustfmt

接着运行 cargo clippy 和 cargo fmt 进行检查，并改进源代码。

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// src/lib.rs
impl Default for KvStore {
    fn default() -> Self {
        Self::new()
    }
}

Extension 1: structopt

使用 structopt crate 代替 clap crate 再来一遍。感觉好烦，不写了