What's the current plan for the implementation of placement new as you envision it? In particular what would the trait used by Gc etc. to hook into it look like? How does it do the thing where expressions are constructed directly into place? I agree with many parts of your analysis (different argument evaluation orders implicitly would indeed be unfortunate), but I want to have a clearer picture of the other alternative before discussing it further.
On Wed, Dec 4, 2013 at 5:57 AM, Patrick Walton <[email protected]> wrote: > I should elaborate: I think you've successfully formulated placement new > in terms of unboxed closures as monomorphized traits whose "call" method > takes self by value. That is, something like (in Rust of the future): > > fn GC<T,F:OnceFunc<T>>(f: F) -> GC<T> > > The difference, though, is that the construction of the closure is > implicit at the call site in this proposal. This is what I'm uncomfortable > with. Rust is a strict language, not a lazy one, and the order of > evaluation of function arguments is one of the things that one has > heretofore been unable to change. I would prefer that a different argument > evaluation order would necessitate some sort of annotation at the call site > (e.g. ocaml's "lazy"). But once you've done that you've essentially > recreated something equivalent to placement new, but more verbose since you > have to name a method when you allocate into an object (e.g. instead of > "box(my_arena) foo" you'd have to write "my_arena.alloc(lazy foo)". I think > we would end up wanting the sugar. > > Patrick > > "Gábor Lehel" <[email protected]> wrote: >> >> Yes, that was one of the things that passed through my mind as well. One >> difference is that those are passed at runtime, whereas here everything >> happens at compile time. I remember LLVM had difficulty reliably optimizing >> runtime closure passing code, like with the old iterators. >> >> >> On Wed, Dec 4, 2013 at 5:05 AM, Daniel Micay <[email protected]>wrote: >> >>> This looks a lot like what stack once functions would provide. >>> >> >> >> >> -- >> Your ship was destroyed in a monadic eruption. >> >> ------------------------------ >> >> Rust-dev mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/rust-dev >> >> > -- > Sent from my Android phone with K-9 Mail. Please excuse my brevity. > -- Your ship was destroyed in a monadic eruption.
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