And again (no need to make a cancelable context) https://go2goplay.golang.org/p/3UFUaXijuX9
On Tue, 1 Dec 2020 at 22:59, roger peppe <rogpe...@gmail.com> wrote: > Slightly simpler again: https://go2goplay.golang.org/p/mKdishv4nhT > > On Tue, 1 Dec 2020 at 18:44, roger peppe <rogpe...@gmail.com> wrote: > >> I'm having difficulty understanding exactly what your code is trying to >> do (and why), and that makes it hard to understand what >> generic solution might be appropriate. >> >> However, here's one alternative implementation that doesn't seem to run >> into the same kind of issues that you did. >> It changes the contract a little bit, but it's still within the spirit, I >> think and it's somewhat simpler: >> >> https://go2goplay.golang.org/p/cEWEUrvfZBl >> >> FWIW when I've implemented this kind of logic in the past, the aim is >> usually to obtain at most one result. I don't really understand the use >> case being implemented here. >> >> To address the actual question you raised: >> >> I ran into the situation where I need to "map" the futures of type >>> *F[int], and *F[T] to *F[timeoutOrResult[T]]. >> >> >> There's no reason why interface types won't still play a large role in >> the future where Go has generics, and that's >> how I'd probably represent timeoutOrResult there, with a dynamic type >> switch to decide which one you've got. >> >> cheers, >> rog. >> >> On Mon, 30 Nov 2020 at 02:09, Matt Joiner <anacro...@gmail.com> wrote: >> >>> I had a muck around with go2 generics with my toy-ish futures package >>> https://github.com/anacrolix/futures. The go1 implementation is in >>> master, and a working go2 implementation in the go2 branch (using channels >>> of different types instead of the attempt that follows). The package >>> provides one function AsCompletedDelayed, that allows to favour futures >>> over others with timeouts. The timeouts are implemented using the future >>> type *F[int], where as the futures the user provides as arguments are >>> *F[T]. In the implementation for AsCompletedDelayed I need to pass both >>> types of futures to another function AsCompleted[T](fs ...*F[T]) <-chan >>> *F[T], then differentiate them when they're returned: I could get back a >>> "timeout" future, or a user/argument future. To do this I created another >>> type timeoutOrResult[T] struct { timeout bool; timeoutIndex int; result T >>> }, however now I ran into the situation where I need to "map" the futures >>> of type *F[int], and *F[T] to *F[timeoutOrResult[T]]. This seems >>> non-trivial: I believe in another language I would make F a Functor, and >>> map the timeouts to something like `Either int T`. It is possible to write >>> an Fmap on my *F type, but now I need to create new types, and break out an >>> interface, and the implementation quickly increases in complexity. >>> >>> This seems like a situation where the go1 style of doing this was easier >>> albeit without enforcing the result types of the futures in the return chan >>> for AsCompleted and AsCompletedDelayed: I could pass arbitrary *Fs to >>> AsCompleted, and then compare the returning *F against a map[*F]struct{} >>> that tracked which ones were timeouts. >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "golang-nuts" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to golang-nuts+unsubscr...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/adb04bb6-bdda-41a9-a168-2541dd912171n%40googlegroups.com >>> <https://groups.google.com/d/msgid/golang-nuts/adb04bb6-bdda-41a9-a168-2541dd912171n%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAJhgaciV6WG1FHOn7X2jpoB6HLZ5c9H_TRXTjTs7z8HwK1KQWw%40mail.gmail.com.
