DIP 1017--Add Bottom Type--Final Review

[aliak]

On Tuesday, 15 January 2019 at 22:44:56 UTC, Johan Engelen wrote:
> The link does not really have answers that explain the use of a 
> bottom type in a practical imperative language, beyond that it 
> signifies `noreturn`.
> The question we have is whether there is a compelling use for 
> "bottom". I'd like to see a real code use case, besides 
> signifying `noreturn` (trivial).

A very practical use case is with error code paths where you end 
up asserting/exiting the program, something like:

int f(int i) {
     if (i) {
         exit(0);
     } else {
         return 0;
     }
}

D currently special cases assert(0) for that. But practically you 
can have function other than a special cased assert that never 
return. Without the bottom type I'd have to write "return 
make-up-a-number" and then if there's a bug in "exit" i could be 
returning make-up-a-number and using it and I'd never be the 
wiser.