1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 //! Provides `P<T>`, a frozen owned smart pointer, as a replacement for `@T` in
16 //! # Motivations and benefits
18 //! * **Identity**: sharing AST nodes is problematic for the various analysis
19 //! passes (e.g. one may be able to bypass the borrow checker with a shared
20 //! `ExprAddrOf` node taking a mutable borrow). The only reason `@T` in the
21 //! AST hasn't caused issues is because of inefficient folding passes which
22 //! would always deduplicate any such shared nodes. Even if the AST were to
23 //! switch to an arena, this would still hold, i.e. it couldn't use `&'a T`,
24 //! but rather a wrapper like `P<'a, T>`.
26 //! * **Immutability**: `P<T>` disallows mutating its inner `T`, unlike `Box<T>`
27 //! (unless it contains an `Unsafe` interior, but that may be denied later).
28 //! This mainly prevents mistakes, but can also enforces a kind of "purity".
30 //! * **Efficiency**: folding can reuse allocation space for `P<T>` and `Vec<T>`,
31 //! the latter even when the input and output types differ (as it would be the
32 //! case with arenas or a GADT AST using type parameters to toggle features).
34 //! * **Maintainability**: `P<T>` provides a fixed interface - `Deref`,
35 //! `and_then` and `map` - which can remain fully functional even if the
36 //! implementation changes (using a special thread-local heap, for example).
37 //! Moreover, a switch to, e.g. `P<'a, T>` would be easy and mostly automated.
39 use std::fmt::{self, Display, Debug};
40 use std::iter::FromIterator;
42 use std::{ptr, slice, vec};
44 use serialize::{Encodable, Decodable, Encoder, Decoder};
46 /// An owned smart pointer.
47 #[derive(Hash, PartialEq, Eq, PartialOrd, Ord)]
48 pub struct P<T: ?Sized> {
52 #[allow(non_snake_case)]
53 /// Construct a `P<T>` from a `T` value.
54 pub fn P<T: 'static>(value: T) -> P<T> {
60 impl<T: 'static> P<T> {
61 /// Move out of the pointer.
62 /// Intended for chaining transformations not covered by `map`.
63 pub fn and_then<U, F>(self, f: F) -> U where
69 /// Transform the inner value, consuming `self` and producing a new `P<T>`.
70 pub fn map<F>(mut self, f: F) -> P<T> where
74 let p = &mut *self.ptr;
75 // FIXME(#5016) this shouldn't need to drop-fill to be safe.
76 ptr::write(p, f(ptr::read_and_drop(p)));
82 impl<T> Deref for P<T> {
85 fn deref<'a>(&'a self) -> &'a T {
90 impl<T: 'static + Clone> Clone for P<T> {
91 fn clone(&self) -> P<T> {
96 impl<T: Debug> Debug for P<T> {
97 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
98 Debug::fmt(&**self, f)
101 impl<T: Display> Display for P<T> {
102 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
103 Display::fmt(&**self, f)
107 impl<T> fmt::Pointer for P<T> {
108 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
109 fmt::Pointer::fmt(&self.ptr, f)
113 impl<T: 'static + Decodable> Decodable for P<T> {
114 fn decode<D: Decoder>(d: &mut D) -> Result<P<T>, D::Error> {
115 Decodable::decode(d).map(P)
119 impl<T: Encodable> Encodable for P<T> {
120 fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
126 impl<T:fmt::Debug> fmt::Debug for P<[T]> {
127 fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
133 pub fn new() -> P<[T]> {
137 pub fn empty() -> P<[T]> {
138 P { ptr: Default::default() }
142 pub fn from_vec(v: Vec<T>) -> P<[T]> {
143 P { ptr: v.into_boxed_slice() }
147 pub fn into_vec(self) -> Vec<T> {
151 pub fn as_slice<'a>(&'a self) -> &'a [T] {
155 pub fn move_iter(self) -> vec::IntoIter<T> {
156 self.into_vec().into_iter()
159 pub fn map<U, F: FnMut(&T) -> U>(&self, f: F) -> P<[U]> {
160 self.iter().map(f).collect()
164 impl<T> Deref for P<[T]> {
167 fn deref(&self) -> &[T] {
172 impl<T> Default for P<[T]> {
173 fn default() -> P<[T]> {
178 impl<T: Clone> Clone for P<[T]> {
179 fn clone(&self) -> P<[T]> {
180 P::from_vec(self.to_vec())
184 impl<T> From<Vec<T>> for P<[T]> {
185 fn from(v: Vec<T>) -> Self {
190 impl<T> Into<Vec<T>> for P<[T]> {
191 fn into(self) -> Vec<T> {
196 impl<T> FromIterator<T> for P<[T]> {
197 fn from_iter<I: IntoIterator<Item=T>>(iter: I) -> P<[T]> {
198 P::from_vec(iter.into_iter().collect())
202 impl<T> IntoIterator for P<[T]> {
204 type IntoIter = vec::IntoIter<T>;
206 fn into_iter(self) -> Self::IntoIter {
207 self.into_vec().into_iter()
211 impl<'a, T> IntoIterator for &'a P<[T]> {
213 type IntoIter = slice::Iter<'a, T>;
214 fn into_iter(self) -> Self::IntoIter {
219 impl<T: Encodable> Encodable for P<[T]> {
220 fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
221 Encodable::encode(&**self, s)
225 impl<T: Decodable> Decodable for P<[T]> {
226 fn decode<D: Decoder>(d: &mut D) -> Result<P<[T]>, D::Error> {
227 Ok(P::from_vec(match Decodable::decode(d) {
229 Err(e) => return Err(e)