Hi,
I think I already asked this question in the past and I'm not very sure
what was the answer and whether it is still applicable wirh rust 0.8.
I'm implementing the double dispatch method overloading such that I can add
2 struct together and a float to a struct.
let data = SomeData{a:1.0} + 2.0;
let data2 = SomeData{a:100.0} + data;
I would like to implement the add for every type of float. I asked whether
I could write something like this:
impl<T:Float> SomeDataRhs for T {
fn add_to(&self, lhs:&SomeData) -> SomeData {
SomeData{a:lhs.a + cast(*self)}
}
}
it does not compile right now with rust 0.8
I get error messages as follow
test2.rs:39:0: 43:1 error: conflicting implementations for trait
`SomeDataRhs`
test2.rs:39 impl SomeDataRhs for SomeData {
test2.rs:40 fn add_to(&self, lhs:&SomeData) -> SomeData {
test2.rs:41 SomeData{a:lhs.a + self.a}
test2.rs:42 }
test2.rs:43 }
test2.rs:33:0: 37:1 note: note conflicting implementation here
test2.rs:33 impl<T:Float> SomeDataRhs for T {
test2.rs:34 fn add_to(&self, lhs:&SomeData) -> SomeData {
test2.rs:35 SomeData{a:lhs.a + cast(*self)}
test2.rs:36 }
Would you know whether what I try to do is possible. I was recommended to
use macro for that, I don't mind to eventually go this way but I would
rather do it the proper way if there is one.
here's the full code of my test:
extern mod std;
use std::num::cast;
struct SomeData { a:float }
trait SomeDataRhs {
fn add_to(&self, lhs:&SomeData) -> SomeData;
}
impl<T:SomeDataRhs> Add<T, SomeData> for SomeData {
fn add(&self, rhs:&T) -> SomeData {
rhs.add_to(self)
}
}
// ---------------
// implementations
// impl SomeDataRhs for float {
// fn add_to(&self, lhs:&SomeData) -> SomeData {
// SomeData{a:lhs.a + *self}
// }
// }
// impl SomeDataRhs for f64 {
// fn add_to(&self, lhs:&SomeData) -> SomeData {
// SomeData{a:lhs.a + cast(*self)}
// }
// }
impl<T:Float> SomeDataRhs for T {
fn add_to(&self, lhs:&SomeData) -> SomeData {
SomeData{a:lhs.a + cast(*self)}
}
}
impl SomeDataRhs for SomeData {
fn add_to(&self, lhs:&SomeData) -> SomeData {
SomeData{a:lhs.a + self.a}
}
}
#[test]
fn test_sandbox() {
let mut data = SomeData{a:1.0} + 2.0;
println!("result: {}", data.a);
let mut data2 = SomeData{a:100.0} + data;
data = data + data2;
println!("result: {}", data.a);
}
cheers,
Rémi
--
Rémi Fontan : [email protected]
mobile: +64 21 855 351
93 Otaki Street, Miramar 6022
Wellington, New Zealand
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