Created
December 19, 2015 03:06
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// Copyright 2015 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. | |
use std::rc::Rc; | |
mod protocol { | |
use std::ptr; | |
pub trait Place<T> { | |
// NOTE(eddyb) The use of `&mut T` here is to force | |
// the LLVM `noalias` and `dereferenceable(sizeof(T))` | |
// attributes, which are required for eliding the copy | |
// and producing actual in-place initialization via RVO. | |
// Neither of those attributes are present on `*mut T`, | |
// but `&mut T` is not a great choice either, the proper | |
// way might be to add those attributes to `Unique<T>`. | |
unsafe fn pointer(&mut self) -> &mut T; | |
} | |
pub trait Boxed<T>: Sized { | |
type P: Place<T>; | |
fn write_and_fin(mut place: Self::P, | |
value: T) | |
-> Self { | |
unsafe { | |
ptr::write(place.pointer(), value); | |
Self::fin(place) | |
} | |
} | |
unsafe fn fin(filled: Self::P) -> Self; | |
} | |
pub fn box_impl<S, T>(value: T) -> S | |
where S: Boxed<T>, S::P: Default | |
{ | |
Boxed::write_and_fin(Default::default(), value) | |
} | |
} | |
macro_rules! box_ { | |
($x:expr) => { | |
::protocol::box_impl($x) | |
} | |
} | |
// Hacky implementations of the box protocol for Box<T> and Rc<T>. | |
// They pass mem::uninitialized() to Box::new, and Rc::new, respectively, | |
// to allocate memory and will leak the allocation in case of unwinding. | |
mod boxed { | |
use std::mem; | |
use protocol; | |
pub struct Place<T> { | |
ptr: *mut T | |
} | |
impl<T> Default for Place<T> { | |
fn default() -> Self { | |
unsafe { | |
Place { | |
ptr: mem::transmute(Box::new(mem::uninitialized::<T>())) | |
} | |
} | |
} | |
} | |
impl<T> protocol::Place<T> for Place<T> { | |
unsafe fn pointer(&mut self) -> &mut T { &mut *self.ptr } | |
} | |
impl<T> protocol::Boxed<T> for Box<T> { | |
type P = Place<T>; | |
unsafe fn fin(place: Place<T>) -> Box<T> { | |
mem::transmute(place.ptr) | |
} | |
} | |
} | |
mod rc { | |
use std::mem; | |
use std::rc::Rc; | |
use protocol; | |
pub struct Place<T> { | |
rc_ptr: *mut (), | |
data_ptr: *mut T | |
} | |
impl<T> Default for Place<T> { | |
fn default() -> Self { | |
unsafe { | |
let rc = Rc::new(mem::uninitialized::<T>()); | |
Place { | |
data_ptr: &*rc as *const _ as *mut _, | |
rc_ptr: mem::transmute(rc) | |
} | |
} | |
} | |
} | |
impl<T> protocol::Place<T> for Place<T> { | |
unsafe fn pointer(&mut self) -> &mut T { | |
&mut *self.data_ptr | |
} | |
} | |
impl<T> protocol::Boxed<T> for Rc<T> { | |
type P = Place<T>; | |
unsafe fn fin(place: Place<T>) -> Rc<T> { | |
mem::transmute(place.rc_ptr) | |
} | |
} | |
} | |
fn main() { | |
let v = vec![1, 2, 3]; | |
let bx: Box<_> = box_!(|| &v); | |
let rc: Rc<_> = box_!(|| &v); | |
assert_eq!(bx(), &v); | |
assert_eq!(rc(), &v); | |
let bx_trait: Box<Fn() -> _> = box_!((|| &v)); | |
let rc_trait: Rc<Fn() -> _> = box_!((|| &v)); | |
assert_eq!(bx(), &v); | |
assert_eq!(rc(), &v); | |
} |
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