pub trait Into<T>: Sized {
// Required method
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 Into
thanks 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.
Generic Implementations
From<T> for UimpliesInto<U> for TIntois reflexive, which means thatInto<T> for Tis implemented
Implementing Into for conversions to external types in old versions of Rust
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
}
}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
}
}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 From
and then fall back to Into if From can’t be implemented.
Examples
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 a
Vec<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);