[swift-evolution] Proposal: An Either Type in the STL

Donnacha Oisín Kidney oisin.kidney at gmail.com
Thu Dec 10 12:57:39 CST 2015

If the analogy is to tuples, though, I would intuitively expect the other behaviour. Maybe something like:

let listOfProducts: [(Int, Bool)] = [(1, true), (2, false)]
let listOfSums: [(Int|Bool)] = [(|true), (2|)]

> On 10 Dec 2015, at 18:38, Joe Groff via swift-evolution <swift-evolution at swift.org> wrote:
>> On Dec 10, 2015, at 10:34 AM, Matthew Johnson <matthew at anandabits.com> wrote:
>>> As an alternative to a semantically-neutral Either type, it might be worth considering the possibility of anonymous structural sum types (similar to how tuples are the structural analog of structs).
>> John mentioned that these are a massive complication for type systems when I proposed them as a possible way to implement throwing multiple error types.  Do you agree with that?
> There are definitely problems if you expect them to behave like unions (so that the type `T + T` == `T`) or be unordered (so that `T + U` == `U + T`), which would be intuitively expected.
> -Joe
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