Recently I came across a function in Rust that returned ! instead of basic type, like this:
fn my_function() -> ! {
// ...
}
What does it mean? I was unable to find piece of information about this in The Rust Book. What data does this function return with such indicator?
It means the function never returns (usually because it unconditionally panics or otherwise ends the program, or because it contains an infinite loop that prevents a return from ever happening).
The appendix describes it as:
!Always empty bottom type for diverging functions
where "diverging" means "never returns".