On 4/22/13 5:54 AM, Huon Wilson wrote:
Hi all,
I've got a few questions:
There are many instances of functions returning and taking dynamic
trait objects in @ boxes (e.g. all of the io functions, things dealing
with core::rand::Rng, core::run::Program) rather than a plain type
(for return values) or a generic (for arguments), this seems a little
peculiar given it (probably?) has a runtime cost due to the vtables
and the extra GC required. Is this legacy code that hasn't been
updated yet? And, is there a reason for it remain in the dynamic
objects form? (I know there's no point touching the io stuff since it
is all being redone.)
You're correct. The `@` smart pointers in `io` are currently the #1
performance problem with Rust in benchmarks that people write. (They're
also responsible for a lot of unsafe code in the benchmarks-game
benchmarks that could otherwise be fully safe.) The new `rt::io` module
[1] is being designed to avoid this. That module will replace `io` when
it's ready.
To give an example, I'm talking about converting items like (all
from core::rand)
fn Rng() -> @Rng
fn rand(rng: @rand::Rng) -> Self
impl RngUtil for @Rng
to
fn Rng() -> RandRes
fn rand<R: rand::Rng>(rng: &R) -> Self
impl<R: Rng> RngUtil for R
Yes, I wanted to do just that at some point. Patches welcome :)
Patrick
[1]: https://github.com/brson/rust/tree/io
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