1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
// run-pass
// If `Mul` used an associated type for its output, this test would
// work more smoothly.
use std::ops::Mul;
#[derive(Copy, Clone)]
struct Vec2 {
x: f64,
y: f64
}
// methods we want to export as methods as well as operators
impl Vec2 {
#[inline(always)]
fn vmul(self, other: f64) -> Vec2 {
Vec2 { x: self.x * other, y: self.y * other }
}
}
// Right-hand-side operator visitor pattern
trait RhsOfVec2Mul {
type Result;
fn mul_vec2_by(&self, lhs: &Vec2) -> Self::Result;
}
// Vec2's implementation of Mul "from the other side" using the above trait
impl<Res, Rhs: RhsOfVec2Mul<Result=Res>> Mul<Rhs> for Vec2 {
type Output = Res;
fn mul(self, rhs: Rhs) -> Res { rhs.mul_vec2_by(&self) }
}
// Implementation of 'f64 as right-hand-side of Vec2::Mul'
impl RhsOfVec2Mul for f64 {
type Result = Vec2;
fn mul_vec2_by(&self, lhs: &Vec2) -> Vec2 { lhs.vmul(*self) }
}
// Usage with failing inference
pub fn main() {
let a = Vec2 { x: 3.0f64, y: 4.0f64 };
// the following compiles and works properly
let v1: Vec2 = a * 3.0f64;
println!("{} {}", v1.x, v1.y);
// the following compiles but v2 will not be Vec2 yet and
// using it later will cause an error that the type of v2
// must be known
let v2 = a * 3.0f64;
println!("{} {}", v2.x, v2.y); // error regarding v2's type
}
|
