53 lines
1.6 KiB
Rust
53 lines
1.6 KiB
Rust
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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use std::io;
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struct Vec2 {
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x: float,
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y: float
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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: float) -> 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<Result> { fn mul_vec2_by(&self, lhs: &Vec2) -> Result; }
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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<Res>> Mul<Rhs,Res> for Vec2 {
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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 'float as right-hand-side of Vec2::Mul'
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impl RhsOfVec2Mul<Vec2> for float {
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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: 3f, y: 4f };
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// the following compiles and works properly
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let v1: Vec2 = a * 3f;
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io::println(fmt!("%f %f", 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 * 3f;
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io::println(fmt!("%f %f", v2.x, v2.y)); // error regarding v2's type
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}
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