枚举到 &str / &str 到枚举

Question

想知道是否有将Enum 转换为&str 并返回的“正确”方式。

我要解决的问题：

在clap crate 中，args/子命令由&strs 定义和标识。 （我假设没有完全利用类型检查器。）我想将 Command Enum 传递给我的应用程序，而不是 &str ，这将由类型检查器和也让我免于在各处输入（打字？）字符串。

这是我通过搜索 StackOverflow 和 std 得出的：

use std::str::FromStr;

#[derive(Debug, Clone, Copy, PartialEq)]
pub enum Command {
    EatCake,
    MakeCake,
}

impl FromStr for Command {
    type Err = ();

    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
        match s.to_ascii_lowercase().as_str() {
            "eat-cake" => Ok(Self::EatCake),
            "make-cake" => Ok(Self::MakeCake),
            _ => Err(()),
        }
    }
}

impl<'a> From<Command> for &'a str {
    fn from(c: Command) -> Self {
        match c {
            Command::EatCake => "eat-cake",
            Command::MakeCake => "make-cake",
        }
    }
}

fn main() {
    let command_from_str: Command = "eat-cake".to_owned().parse().unwrap();
    let str_from_command: &str = command_from_str.into();

    assert_eq!(command_from_str, Command::EatCake);
    assert_eq!(str_from_command, "eat-cake");
}

这是一个工作场所： https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=b5e9ac450fd6a79b855306e96d4707fa

这是我在clap 中运行的内容的精简版。

let matches = App::new("cake")
    .setting(AppSettings::SubcommandRequiredElseHelp)
    // ...
    .subcommand(
        SubCommand::with_name(Command::MakeCake.into())
            // ...
    )
    .subcommand(
        SubCommand::with_name(Command::EatCake.into())
            // ...
    )
    .get_matches();

它似乎有效，但我不确定我是否遗漏了什么/更大的图景。

相关：

• How to use an internal library Enum for Clap Args
• How do I return an error within match statement while implementing from_str in rust?

谢谢！

Answer 1

strum crate 可以为您节省一些工作。使用strum，我能够得到简单的main()，您无需任何额外的From 实现即可工作。

use strum_macros::{Display, EnumString, IntoStaticStr};

#[derive(Debug, Clone, Copy, PartialEq)]
#[derive(Display, EnumString, IntoStaticStr)]  // strum macros.
pub enum Command {
    #[strum(serialize = "eat-cake")]
    EatCake,
    
    #[strum(serialize = "make-cake")]
    MakeCake,
}
fn main() {
    let command_from_str: Command = "eat-cake".to_owned().parse().unwrap();
    let str_from_command: &str    = command_from_str.into();

    assert_eq!(command_from_str, Command::EatCake);
    assert_eq!(str_from_command, "eat-cake");
}