Rust- 类型转换

Rust is a statically typed language, which means that it emphasizes on knowing the types of all variables at compile time. The concept of type safety is very crucial in Rust, and the language provides several mechanisms for type conversion.

Type conversion in Rust is explicit, meaning that you need to specify the type you want to convert to.

Here are two common forms of type conversion in Rust:

1. Casting: Rust uses the as keyword to perform basic casting between primitive types. For instance:

   let num = 5.6;
   let integer: i32 = num as i32;  // `integer` will be 5
   

   It’s important to note that casting with as can be unsafe, especially when casting between types of different sizes. For example, casting from a larger integer type to a smaller one (like from u32 to u8) can lead to data loss.

2. From/Into Traits: The From and Into traits are used for more complex conversions. The From trait allows a type to define how to create itself from another type, while the Into trait is the reciprocal of the From trait.

   let my_str = "5";
   let num: i32 = my_str.parse().unwrap();  // `num` will be 5
   

   In the above code, we used parse function which is based on the FromStr trait to convert a string slice into an i32.

   Similarly, we can use From/Into for user-defined conversions:

   #[derive(Debug)]
   struct Number {
       value: i32,
   }
   
   impl From<i32> for Number {
       fn from(item: i32) -> Self {
           Number { value: item }
       }
   }
   
   fn main() {
       let num = Number::from(30);
       println!("My number is {:?}", num);
   }
   

   This example creates a Number struct from an i32 using the From trait.

In all these examples, type conversion is explicit and checked at compile time, adding to the safety and robustness of Rust.

fn main() {
    let s1 = "Rust";
    let s2 = String::from(s1);

    let my_number = MyNumber::from(1);
    println!("{:?}", my_number); // MyNumber { num: 1 }

    let spend = 3;
    let my_spend: MyNumber = spend.into();
    println!("{:?}", my_spend); // MyNumber { num: 3 }

    let cost: i32 = "5".parse().unwrap();
    println!("{}", cost);       // 5
}

#[derive(Debug)]
struct MyNumber {
    num: i32,
}

impl From<i32> for MyNumber {
    fn from(value: i32) -> Self {
        MyNumber { num: value }
    }
}