Type Definition std::convert::Infallible

type Infallible = !;

A type alias for the ! “never” type.

Infallible represents types of errors that can never happen since ! has no valid values. This can be useful for generic APIs that use Result and parameterize the error type, to indicate that the result is always Ok.

For example, the TryFrom trait (conversion that returns a Result) has a blanket implementation for all types where a reverse Into implementation exists.

impl<T, U> TryFrom<U> for T where U: Into<T> {
    type Error = Infallible;

    fn try_from(value: U) -> Result<Self, Infallible> {
        Ok(U::into(value))  // Never returns `Err`
    }
}

Eventual deprecation

Previously, Infallible was defined as enum Infallible {}. Now that it is merely a type alias to !, we will eventually deprecate Infallible.