rust - 自动将字符串解析为最合适的类型

Question

如何将某些字符串解析为最合适的类型？
我知道有.parse::<>()方法，但是您需要像这样预先指定类型:

fn main() {
    let val = String::from("54");
    assert_eq!(val.parse::<i32>().unwrap(), 54i32);
    
    let val = String::from("3.14159");
    assert_eq!(val.parse::<f32>().unwrap(), 3.14159f32);
    
    let val = String::from("Hello!");
    assert_eq!(val.parse::<String>().unwrap(), "Hello!".to_string());
}

但是我需要这样的东西:

fn main() {
    let val = String::from("54");
    assert_eq!(val.generic_parse().unwrap(), 54i32); // or 54i16 or 54 u32 or etc ...
    
    let val = String::from("3.14159");
    assert_eq!(val.generic_parse().unwrap(), 3.14159f32);
    
    let val = String::from("Hello!");
    assert_eq!(val.generic_parse().unwrap(), "Hello!".to_string());
}

是否有合适的箱子可用于这种情况？我不想在第十次重新发明轮子。
编辑
这是我实际上要执行的操作:

struct MyStruct<T> {
    generic_val: T,
}

fn main() {
    let val = String::from("54");
    let b = MyStruct {generic_val: val.parse().unwrap()};
    
    let val = String::from("3.14159");
    let b = MyStruct {generic_val: val.parse().unwrap()};
}

错误:

error[E0282]: type annotations needed for `MyStruct<T>`
 --> src/main.rs:7:13
  |
7 |     let b = MyStruct {generic_val: val.parse().unwrap()};
  |         -   ^^^^^^^^ cannot infer type for type parameter `T` declared on the struct `MyStruct`
  |         |
  |         consider giving `b` the explicit type `MyStruct<T>`, where the type parameter `T` is specified

Answer 1

您需要以正确的Enum类型为基础，并为其实现FromStr。像这样。

#[derive(PartialEq, Debug)]
enum Val {
    Isize(isize),
    F64(f64),
}

impl core::str::FromStr for Val {
    type Err = & 'static str;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match (s.parse::<isize>(), s.parse::<f64>()) {
            (Ok(i),_) => Ok(Val::Isize(i)),
            (Err(_), Ok(f)) => Ok(Val::F64(f)),
            (Err(_), Err(_)) => Err("neither parser worked"),
        }
    }
}

 fn main() {
    assert_eq!("34".parse(), Ok(Val::Isize(34)));
    assert_eq!("12.3".parse(), Ok(Val::F64(12.3)));
    assert!("wrong".parse::<Val>().is_err());
}