| // Copyright 2013 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| // 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 |
| } |