src/libsyntax/ptr.rs

   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.
   4 //
   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.
  10
  11 //! The AST pointer
  12 //!
  13 //! Provides `P<T>`, a frozen owned smart pointer, as a replacement for `@T` in
  14 //! the AST.
  15 //!
  16 //! # Motivations and benefits
  17 //!
  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>`.
  25 //!
  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".
  29 //!
  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).
  33 //!
  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.
  38
  39 use std::fmt::{self, Display, Debug};
  40 use std::iter::FromIterator;
  41 use std::ops::Deref;
  42 use std::{ptr, slice, vec};
  43
  44 use serialize::{Encodable, Decodable, Encoder, Decoder};
  45
  46 /// An owned smart pointer.
  47 #[derive(Hash, PartialEq, Eq, PartialOrd, Ord)]
  48 pub struct P<T: ?Sized> {
  49     ptr: Box<T>
  50 }
  51
  52 #[allow(non_snake_case)]
  53 /// Construct a `P<T>` from a `T` value.
  54 pub fn P<T: 'static>(value: T) -> P<T> {
  55     P {
  56         ptr: Box::new(value)
  57     }
  58 }
  59
  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
  64         F: FnOnce(T) -> U,
  65     {
  66         f(*self.ptr)
  67     }
  68
  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
  71         F: FnOnce(T) -> T,
  72     {
  73         unsafe {
  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)));
  77         }
  78         self
  79     }
  80 }
  81
  82 impl<T> Deref for P<T> {
  83     type Target = T;
  84
  85     fn deref<'a>(&'a self) -> &'a T {
  86         &*self.ptr
  87     }
  88 }
  89
  90 impl<T: 'static + Clone> Clone for P<T> {
  91     fn clone(&self) -> P<T> {
  92         P((**self).clone())
  93     }
  94 }
  95
  96 impl<T: Debug> Debug for P<T> {
  97     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  98         Debug::fmt(&**self, f)
  99     }
 100 }
 101 impl<T: Display> Display for P<T> {
 102     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 103         Display::fmt(&**self, f)
 104     }
 105 }
 106
 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)
 110     }
 111 }
 112
 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)
 116     }
 117 }
 118
 119 impl<T: Encodable> Encodable for P<T> {
 120     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 121         (**self).encode(s)
 122     }
 123 }
 124
 125
 126 impl<T:fmt::Debug> fmt::Debug for P<[T]> {
 127     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
 128         self.ptr.fmt(fmt)
 129     }
 130 }
 131
 132 impl<T> P<[T]> {
 133     pub fn new() -> P<[T]> {
 134         P::empty()
 135     }
 136
 137     pub fn empty() -> P<[T]> {
 138         P { ptr: Default::default() }
 139     }
 140
 141     #[inline(never)]
 142     pub fn from_vec(v: Vec<T>) -> P<[T]> {
 143         P { ptr: v.into_boxed_slice() }
 144     }
 145
 146     #[inline(never)]
 147     pub fn into_vec(self) -> Vec<T> {
 148         self.ptr.into_vec()
 149     }
 150
 151     pub fn as_slice<'a>(&'a self) -> &'a [T] {
 152         &*self.ptr
 153     }
 154
 155     pub fn move_iter(self) -> vec::IntoIter<T> {
 156         self.into_vec().into_iter()
 157     }
 158
 159     pub fn map<U, F: FnMut(&T) -> U>(&self, f: F) -> P<[U]> {
 160         self.iter().map(f).collect()
 161     }
 162 }
 163
 164 impl<T> Deref for P<[T]> {
 165     type Target = [T];
 166
 167     fn deref(&self) -> &[T] {
 168         self.as_slice()
 169     }
 170 }
 171
 172 impl<T> Default for P<[T]> {
 173     fn default() -> P<[T]> {
 174         P::empty()
 175     }
 176 }
 177
 178 impl<T: Clone> Clone for P<[T]> {
 179     fn clone(&self) -> P<[T]> {
 180         P::from_vec(self.to_vec())
 181     }
 182 }
 183
 184 impl<T> From<Vec<T>> for P<[T]> {
 185     fn from(v: Vec<T>) -> Self {
 186         P::from_vec(v)
 187     }
 188 }
 189
 190 impl<T> Into<Vec<T>> for P<[T]> {
 191     fn into(self) -> Vec<T> {
 192         self.into_vec()
 193     }
 194 }
 195
 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())
 199     }
 200 }
 201
 202 impl<T> IntoIterator for P<[T]> {
 203     type Item = T;
 204     type IntoIter = vec::IntoIter<T>;
 205
 206     fn into_iter(self) -> Self::IntoIter {
 207         self.into_vec().into_iter()
 208     }
 209 }
 210
 211 impl<'a, T> IntoIterator for &'a P<[T]> {
 212     type Item = &'a T;
 213     type IntoIter = slice::Iter<'a, T>;
 214     fn into_iter(self) -> Self::IntoIter {
 215         self.ptr.into_iter()
 216     }
 217 }
 218
 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)
 222     }
 223 }
 224
 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) {
 228             Ok(t) => t,
 229             Err(e) => return Err(e)
 230         }))
 231     }
 232 }