56290a0044
This commit is an implementation of [RFC 503][rfc] which is a stabilization story for the prelude. Most of the RFC was directly applied, removing reexports. Some reexports are kept around, however: * `range` remains until range syntax has landed to reduce churn. * `Path` and `GenericPath` remain until path reform lands. This is done to prevent many imports of `GenericPath` which will soon be removed. * All `io` traits remain until I/O reform lands so imports can be rewritten all at once to `std::io::prelude::*`. This is a breaking change because many prelude reexports have been removed, and the RFC can be consulted for the exact list of removed reexports, as well as to find the locations of where to import them. [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0503-prelude-stabilization.md [breaking-change] Closes #20068
123 lines
3.7 KiB
Rust
123 lines
3.7 KiB
Rust
// Copyright 2014 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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//! The AST pointer
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//!
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//! Provides `P<T>`, a frozen owned smart pointer, as a replacement for `@T` in
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//! the AST.
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//!
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//! # Motivations and benefits
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//!
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//! * **Identity**: sharing AST nodes is problematic for the various analysis
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//! passes (e.g. one may be able to bypass the borrow checker with a shared
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//! `ExprAddrOf` node taking a mutable borrow). The only reason `@T` in the
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//! AST hasn't caused issues is because of inefficient folding passes which
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//! would always deduplicate any such shared nodes. Even if the AST were to
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//! switch to an arena, this would still hold, i.e. it couldn't use `&'a T`,
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//! but rather a wrapper like `P<'a, T>`.
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//!
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//! * **Immutability**: `P<T>` disallows mutating its inner `T`, unlike `Box<T>`
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//! (unless it contains an `Unsafe` interior, but that may be denied later).
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//! This mainly prevents mistakes, but can also enforces a kind of "purity".
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//!
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//! * **Efficiency**: folding can reuse allocation space for `P<T>` and `Vec<T>`,
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//! the latter even when the input and output types differ (as it would be the
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//! case with arenas or a GADT AST using type parameters to toggle features).
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//!
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//! * **Maintainability**: `P<T>` provides a fixed interface - `Deref`,
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//! `and_then` and `map` - which can remain fully functional even if the
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//! implementation changes (using a special thread-local heap, for example).
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//! Moreover, a switch to, e.g. `P<'a, T>` would be easy and mostly automated.
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use std::fmt::{mod, Show};
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use std::hash::Hash;
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use std::ops::Deref;
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use std::ptr;
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use serialize::{Encodable, Decodable, Encoder, Decoder};
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/// An owned smart pointer.
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pub struct P<T> {
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ptr: Box<T>
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}
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#[allow(non_snake_case)]
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/// Construct a `P<T>` from a `T` value.
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pub fn P<T: 'static>(value: T) -> P<T> {
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P {
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ptr: box value
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}
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}
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impl<T: 'static> P<T> {
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/// Move out of the pointer.
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/// Intended for chaining transformations not covered by `map`.
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pub fn and_then<U, F>(self, f: F) -> U where
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F: FnOnce(T) -> U,
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{
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f(*self.ptr)
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}
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/// Transform the inner value, consuming `self` and producing a new `P<T>`.
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pub fn map<F>(mut self, f: F) -> P<T> where
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F: FnOnce(T) -> T,
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{
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unsafe {
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let p = &mut *self.ptr;
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// FIXME(#5016) this shouldn't need to zero to be safe.
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ptr::write(p, f(ptr::read_and_zero(p)));
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}
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self
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}
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}
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impl<T> Deref<T> for P<T> {
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fn deref<'a>(&'a self) -> &'a T {
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&*self.ptr
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}
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}
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impl<T: 'static + Clone> Clone for P<T> {
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fn clone(&self) -> P<T> {
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P((**self).clone())
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}
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}
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impl<T: PartialEq> PartialEq for P<T> {
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fn eq(&self, other: &P<T>) -> bool {
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**self == **other
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}
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}
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impl<T: Eq> Eq for P<T> {}
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impl<T: Show> Show for P<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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(**self).fmt(f)
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}
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}
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impl<S, T: Hash<S>> Hash<S> for P<T> {
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fn hash(&self, state: &mut S) {
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(**self).hash(state);
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}
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}
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impl<E, D: Decoder<E>, T: 'static + Decodable<D, E>> Decodable<D, E> for P<T> {
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fn decode(d: &mut D) -> Result<P<T>, E> {
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Decodable::decode(d).map(P)
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}
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}
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impl<E, S: Encoder<E>, T: Encodable<S, E>> Encodable<S, E> for P<T> {
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fn encode(&self, s: &mut S) -> Result<(), E> {
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(**self).encode(s)
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}
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}
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