Hmm, right. The as_* could probably useful to write a macro for.
Coming from the C/Java side of things I have to figure out how this
works in a bigger context, e g a DList or other structure owning objects
implementing HasArea. This seems to compile, e g:
impl Pancake {
fn as_box_circle(&self) -> Box<Circle> { box self.circle }
}
fn make_pancake(dl: &mut DList<Box<HasArea>>) {
let p = Pancake { circle: Circle { x: 0f64, y: 0f64, radius: 1f64
}, is_tasty: true };
dl.push(p.as_box_circle());
}
But I'd assume that make_pancake would now make a copy of the pancake's
circle, rather than taking ownership of the entire pancake, right? The
pancake then gets dropped at function return.
In this simple example perhaps this does not make that much of a
difference though, but if you imagine a C struct like:
struct list {
list *next;
circle *data;
}
You can now put a pointer to a pancake as data, use it as a circle, and
when you finally free the list and the data that goes with it, the
entire pancake will be freed. This you cannot do in rust...or can you?
On 2014-10-17 07:59, Clark Gaebel wrote:
impl Pancake {
fn as_circle(&self) -> &Circle { &self.circle }
fn as_mut_circle(&mut self) -> &mut Circle { &mut self.circle }
}
The compiler will optimize trivial functions, except cross-crate. In
those cases, use an #[inline] annotation.
On Thu, Oct 16, 2014 at 10:57 PM, David Henningsson <[email protected]
<mailto:[email protected]>> wrote:
This is probably a previously asked question, but I couldn't find
it on
Google, so...
Let's extend the Circle example from the guide a little:
struct Circle {
x:f64,
y:f64,
radius:f64,
}
trait HasArea {
fn area(&self)-> f64;
}
impl HasArea for Circle {
fn area(&self)-> f64 {
std::f64::consts::PI * (self.radius * self.radius)
}
}
struct Pancake {
circle: Circle,
is_tasty: bool,
}
...now, what is the easiest way I can implement HasArea for
Pancake? I
could do this:
impl HasArea for Pancake {
fn area(&self) -> f64 { self.circle.area() }
}
...but that means a lot of boiler-plate code, especially if
HasArea has
many methods. Hopefully rust will just inline/optimise the
redirection
away in most cases to avoid the runtime cost, but is there a
smarter or
more idiomatic way of doing this?
// David
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