Into in std::convert - Rust (original) (raw)

pub trait Into<T> {
    fn into(self) -> T;
}

Expand description

A value-to-value conversion that consumes the input value. The opposite of From.

One should avoid implementing Into and implement From instead. Implementing From automatically provides one with an implementation of Intothanks to the blanket implementation in the standard library.

Prefer using Into over From when specifying trait bounds on a generic function to ensure that types that only implement Into can be used as well.

Note: This trait must not fail. If the conversion can fail, use TryInto.

Prior to Rust 1.41, if the destination type was not part of the current crate then you couldn’t implement From directly. For example, take this code:

struct Wrapper<T>(Vec<T>);
impl<T> From<Wrapper<T>> for Vec<T> {
    fn from(w: Wrapper<T>) -> Vec<T> {
        w.0
    }
}

Run

This will fail to compile in older versions of the language because Rust’s orphaning rules used to be a little bit more strict. To bypass this, you could implement Into directly:

struct Wrapper<T>(Vec<T>);
impl<T> Into<Vec<T>> for Wrapper<T> {
    fn into(self) -> Vec<T> {
        self.0
    }
}

Run

It is important to understand that Into does not provide a From implementation (as From does with Into). Therefore, you should always try to implement Fromand then fall back to Into if From can’t be implemented.

String implements Into<Vec<u8>>:

In order to express that we want a generic function to take all arguments that can be converted to a specified type T, we can use a trait bound of Into<T>. For example: The function is_hello takes all arguments that can be converted into aVec<u8>.

fn is_hello<T: Into<Vec<u8>>>(s: T) {
   let bytes = b"hello".to_vec();
   assert_eq!(bytes, s.into());
}

let s = "hello".to_string();
is_hello(s);

Run

impl<T, U> Into for T where

U: From,