>>> 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.
>>
>> I think it would be more useful if the compiler allowed `Never` in every
>> type context (i.e. whatever type `T` was expected, an expression of type
>> `Never` would be allowed), making expressions like the following compile:
>>
>> let unwrapped: Int = optional ?? fatalError("explanation why this must
>> not happen")
>>
>> — Pyry
>
> I dunno, I think @noreturn is clearer than any of these. It tells you that
> the function… won’t return. None, Never, etc. could be mistaken as a synonym
> for Void, whereas @noreturn is pretty hard to miss.
FWIW, in the rejection of SE-0097
<https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160530/019879.html>,
this was what the core team had to say about it:
1) For noreturn, the core team prefers to explore a solution where a function
can be declared as returning an non-constructable “bottom” type (e.g. an enum
with zero cases). This would lead to something like:
func abort() -> NoReturn { … }
This will require some new support in the compiler, but should flow better
through the type system than @noreturn in function composition and other
applications. Joe Groff offered to write a proposal for this.
— Pyry
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