On 7/22/14 10:16 AM, Lionel Parreaux wrote:
I'm not sure whether this is a big problem in practice, but I was wondering if it would be possible to switch to some runtime mechanism in cases like this. Maybe we could make a special version of every generic functions, that takes a dictionary at runtime and that would be able to handle types unknown at compile-time. We would switch to this version when monomorphization does not work. It could also allow dynamic linking of libraries with generic functions, or it could be a way to compile some programs (or some parts of programs) much faster.
The hard part about doing that is not the dictionary passing. The hard part is that generic types may have unknown size or alignment. In Haskell this is not a problem because the language is garbage-collected and lazy so values have a uniform representation. But in Rust this is not true.
Old Rust used to try to use runtime dictionary passing, where the dictionary contained size and alignment information, and all size/alignment info was computed at runtime for generics. I cannot overstate how *fiendishly* complex this was. We never got all the bugs out. In many cases, the amount of runtime code generated to compute size and alignment outweighed the cost of just monomorphizing.
I strongly feel that the current system, where you can use generic type parameters to get monomorphization or trait objects to get dictionary passing, is the sweet spot.
Patrick _______________________________________________ Rust-dev mailing list Rust-dev@mozilla.org https://mail.mozilla.org/listinfo/rust-dev
