Type Alias Never 

pub type Never = Infallible;

Never cannot be constructed as it’s an enum with no variants. So it’s perfect to denote a signal that will never be emitted, like Observables that never error, or emit. Or Operators who catch errors.

Never is really just a type alias for the built in Infallible type, but the name Infallible limits its meaning to errors for the Result type, while Never is about events/signals of any kinds that can never happen.

Aliased Type

pub enum Never {}