I vote for Bottom or Never. None does not convey "this should not occur or be evaluated".
On Sun, Jun 5, 2016 at 2:26 PM, Антон Жилин <[email protected]> wrote: > The following names were suggested: NoReturn, Bottom, None, Never. > I would pick None, because it looks like opposite to Any and fits nicely > in generic types. > > I would prefer the type to be simple, and be implemented as a case-less > enum (not a bottom value, as in Haskell). > > None should be a usual enum, with no compiler magic except that functions > returning None are equivalent to current @noreturn. > > Example 1. > let x: None? > // ... > let y = x! > > It will trap in runtime not because we discover scary bottom thing, as in > Haskell, but because x had value Optional.none at that moment and we > asserted otherwise. > We could prove that it is always true in this case, but compiler must be > stupid about this. > > Example 2. > Compiler should allow including None in structures. Error will show up in > constructor, when we will not be able to initialize the field. > > Example 3. > None in an enum case makes that case never appear in values of such a > type. But compiler can not know about that. > > - Anton > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution > >
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