What is the From and Into trait

Type System
2026-04-17T12:05:42+00:00
The From and Into traits enable automatic, safe type conversions in Rust by defining a single implementation that works in both directions.

The From and Into traits are standard Rust traits that define how to convert between different types, with From implementing the conversion logic and Into automatically delegating to From.

use std::str::FromStr;

fn main() {
    // From: Convert String to &str (explicit implementation)
    let s: String = "hello".to_string();
    let slice: &str = s.as_str(); // Uses Into implicitly

    // Into: Convert &str to String (auto-implemented if From exists)
    let s2: String = "world".into();

    // Custom example: Convert u32 to MyType
    struct MyType(u32);
    impl From<u32> for MyType {
        fn from(val: u32) -> Self {
            MyType(val)
        }
    }
    let my_val: MyType = 42.into(); // Works because From<u32> is implemented
}