On 15/11/13 18:47, Oren Ben-Kiki wrote:
In your code, when providing a default implementation for
`inflate_by`, you are invoking the trait (hence "virtual")
method `get_radius`. If the compiler compiles `inflate_by` when seeing
just the `Inflate` source code, then this must be translated to an
indirect call through the vtable.
The point of anonymous members (and, to a greater extent, of the
single inheritance) is to ensure that access to data members is just
that, without any function calls.
To achieve that with the approach you described, the compiler will
need to re-compile `inflate_by` for each and every struct that
implements it; only then it would be able to inline `get_radius`.
Is this what the Rust compiler does today? I have no specific
knowledge of the answer, but the simplest thing for the compiler would
be to keep `get_radius` as a virtual function call.
As I understand it, default methods are specialised/monomorphised for
each type for which the trait is implemented. The only time a virtual
call ever happens is when one explicitly has a trait object.
Huon
Doing otherwise would require quite a bit of machinery (e.g., what
if `Inflate` is defined in another crate, and all we have is its
fully-compiled shared object file? There would need to be some "extra
stuff" available to the compiler to do this re-compilation, as the
source is not available at that point).
Therefore I suspect that this approach would suffer from significant
performance issues.
On 2013-11-15, at 2:09, Tommi <[email protected]
<mailto:[email protected]>> wrote:
trait Inflate {
fn get_radius<'s>(&'s mut self) -> &'s mut int;
fn inflate_by(&mut self, amount: int) {
*self.get_radius() += amount;
}
}
trait Flatten {
fn get_radius<'s>(&'s mut self) -> &'s mut int;
fn release_all_air(&mut self) {
*self.get_radius() = 0;
}
}
struct Balloon {
radius: int
}
impl Inflate for Balloon {
fn get_radius<'s>(&'s mut self) -> &'s mut int {
&mut self.radius
}
}
impl Flatten for Balloon {
fn get_radius<'s>(&'s mut self) -> &'s mut int {
&mut self.radius
}
}
_______________________________________________
Rust-dev mailing list
[email protected]
https://mail.mozilla.org/listinfo/rust-dev
_______________________________________________
Rust-dev mailing list
[email protected]
https://mail.mozilla.org/listinfo/rust-dev
