56 lines
1.3 KiB
Rust
56 lines
1.3 KiB
Rust
// run-pass
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// If `Mul` used an associated type for its output, this test would
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// work more smoothly.
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use std::ops::Mul;
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#[derive(Copy, Clone)]
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struct Vec2 {
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x: f64,
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y: f64
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}
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// methods we want to export as methods as well as operators
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impl Vec2 {
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#[inline(always)]
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fn vmul(self, other: f64) -> Vec2 {
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Vec2 { x: self.x * other, y: self.y * other }
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}
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}
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// Right-hand-side operator visitor pattern
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trait RhsOfVec2Mul {
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type Result;
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fn mul_vec2_by(&self, lhs: &Vec2) -> Self::Result;
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}
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// Vec2's implementation of Mul "from the other side" using the above trait
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impl<Res, Rhs: RhsOfVec2Mul<Result=Res>> Mul<Rhs> for Vec2 {
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type Output = Res;
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fn mul(self, rhs: Rhs) -> Res { rhs.mul_vec2_by(&self) }
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}
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// Implementation of 'f64 as right-hand-side of Vec2::Mul'
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impl RhsOfVec2Mul for f64 {
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type Result = Vec2;
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fn mul_vec2_by(&self, lhs: &Vec2) -> Vec2 { lhs.vmul(*self) }
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}
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// Usage with failing inference
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pub fn main() {
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let a = Vec2 { x: 3.0f64, y: 4.0f64 };
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// the following compiles and works properly
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let v1: Vec2 = a * 3.0f64;
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println!("{} {}", v1.x, v1.y);
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// the following compiles but v2 will not be Vec2 yet and
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// using it later will cause an error that the type of v2
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// must be known
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let v2 = a * 3.0f64;
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println!("{} {}", v2.x, v2.y); // error regarding v2's type
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}
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