On Thu, Nov 07, 2013 at 04:48:06PM -0500, Daniel Micay wrote:
> Owned boxes shouldn't be commonly used. There's close to no reason to use
> one for anything but a recursive data structure or in rare cases for an
> owned trait object.
I don't really agree with this statement. I agree that those are the
two cases an owned pointer is mandatory, and that the choice between
`T` and `~T` is a matter of optimization, and hence something that
should be measured.
However, I don't think it's *so* unusual that one might want
pointer-sized values. Off the top of my head, here are some more
scenarios where owned pointers certainly make sense:
1. Options, particularly those that are frequently none.
`Option<~HashMap<...>>` is a single word in size. If it is
`None`, that's just a NULL pointer.
2. Enum variants. The size of an enum is the size of its largest
variant. If you have:
enum Foo {
Opt1(uint),
Opt2(HashMap<...>),
Opt3(uint, uint, uint),
}
You are potentially wasting a lot of space, unless `Opt1` is very
rare. You'd be better off doing something like:
enum Foo {
Opt1(uint),
Opt2(~HashMap<...>),
Opt3(~Opt3)
}
struct Opt3 { uint, uint, uint }
Niko
_______________________________________________
Rust-dev mailing list
[email protected]
https://mail.mozilla.org/listinfo/rust-dev
