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Diffstat (limited to 'compiler/rustc_ast/src/ptr.rs')
-rw-r--r-- | compiler/rustc_ast/src/ptr.rs | 212 |
1 files changed, 212 insertions, 0 deletions
diff --git a/compiler/rustc_ast/src/ptr.rs b/compiler/rustc_ast/src/ptr.rs new file mode 100644 index 000000000..30481eddf --- /dev/null +++ b/compiler/rustc_ast/src/ptr.rs @@ -0,0 +1,212 @@ +//! The AST pointer. +//! +//! Provides `P<T>`, a frozen owned smart pointer. +//! +//! # Motivations and benefits +//! +//! * **Identity**: sharing AST nodes is problematic for the various analysis +//! passes (e.g., one may be able to bypass the borrow checker with a shared +//! `ExprKind::AddrOf` node taking a mutable borrow). +//! +//! * **Immutability**: `P<T>` disallows mutating its inner `T`, unlike `Box<T>` +//! (unless it contains an `Unsafe` interior, but that may be denied later). +//! This mainly prevents mistakes, but also enforces a kind of "purity". +//! +//! * **Efficiency**: folding can reuse allocation space for `P<T>` and `Vec<T>`, +//! the latter even when the input and output types differ (as it would be the +//! case with arenas or a GADT AST using type parameters to toggle features). +//! +//! * **Maintainability**: `P<T>` provides a fixed interface - `Deref`, +//! `and_then` and `map` - which can remain fully functional even if the +//! implementation changes (using a special thread-local heap, for example). +//! Moreover, a switch to, e.g., `P<'a, T>` would be easy and mostly automated. + +use std::fmt::{self, Debug, Display}; +use std::iter::FromIterator; +use std::ops::{Deref, DerefMut}; +use std::{slice, vec}; + +use rustc_serialize::{Decodable, Decoder, Encodable, Encoder}; + +use rustc_data_structures::stable_hasher::{HashStable, StableHasher}; +/// An owned smart pointer. +pub struct P<T: ?Sized> { + ptr: Box<T>, +} + +/// Construct a `P<T>` from a `T` value. +#[allow(non_snake_case)] +pub fn P<T: 'static>(value: T) -> P<T> { + P { ptr: Box::new(value) } +} + +impl<T: 'static> P<T> { + /// Move out of the pointer. + /// Intended for chaining transformations not covered by `map`. + pub fn and_then<U, F>(self, f: F) -> U + where + F: FnOnce(T) -> U, + { + f(*self.ptr) + } + + /// Equivalent to `and_then(|x| x)`. + pub fn into_inner(self) -> T { + *self.ptr + } + + /// Produce a new `P<T>` from `self` without reallocating. + pub fn map<F>(mut self, f: F) -> P<T> + where + F: FnOnce(T) -> T, + { + let x = f(*self.ptr); + *self.ptr = x; + + self + } + + /// Optionally produce a new `P<T>` from `self` without reallocating. + pub fn filter_map<F>(mut self, f: F) -> Option<P<T>> + where + F: FnOnce(T) -> Option<T>, + { + *self.ptr = f(*self.ptr)?; + Some(self) + } +} + +impl<T: ?Sized> Deref for P<T> { + type Target = T; + + fn deref(&self) -> &T { + &self.ptr + } +} + +impl<T: ?Sized> DerefMut for P<T> { + fn deref_mut(&mut self) -> &mut T { + &mut self.ptr + } +} + +impl<T: 'static + Clone> Clone for P<T> { + fn clone(&self) -> P<T> { + P((**self).clone()) + } +} + +impl<T: ?Sized + Debug> Debug for P<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + Debug::fmt(&self.ptr, f) + } +} + +impl<T: Display> Display for P<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + Display::fmt(&**self, f) + } +} + +impl<T> fmt::Pointer for P<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Pointer::fmt(&self.ptr, f) + } +} + +impl<D: Decoder, T: 'static + Decodable<D>> Decodable<D> for P<T> { + fn decode(d: &mut D) -> P<T> { + P(Decodable::decode(d)) + } +} + +impl<S: Encoder, T: Encodable<S>> Encodable<S> for P<T> { + fn encode(&self, s: &mut S) { + (**self).encode(s); + } +} + +impl<T> P<[T]> { + pub const fn new() -> P<[T]> { + P { ptr: Box::default() } + } + + #[inline(never)] + pub fn from_vec(v: Vec<T>) -> P<[T]> { + P { ptr: v.into_boxed_slice() } + } + + #[inline(never)] + pub fn into_vec(self) -> Vec<T> { + self.ptr.into_vec() + } +} + +impl<T> Default for P<[T]> { + /// Creates an empty `P<[T]>`. + fn default() -> P<[T]> { + P::new() + } +} + +impl<T: Clone> Clone for P<[T]> { + fn clone(&self) -> P<[T]> { + P::from_vec(self.to_vec()) + } +} + +impl<T> From<Vec<T>> for P<[T]> { + fn from(v: Vec<T>) -> Self { + P::from_vec(v) + } +} + +impl<T> Into<Vec<T>> for P<[T]> { + fn into(self) -> Vec<T> { + self.into_vec() + } +} + +impl<T> FromIterator<T> for P<[T]> { + fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> P<[T]> { + P::from_vec(iter.into_iter().collect()) + } +} + +impl<T> IntoIterator for P<[T]> { + type Item = T; + type IntoIter = vec::IntoIter<T>; + + fn into_iter(self) -> Self::IntoIter { + self.into_vec().into_iter() + } +} + +impl<'a, T> IntoIterator for &'a P<[T]> { + type Item = &'a T; + type IntoIter = slice::Iter<'a, T>; + fn into_iter(self) -> Self::IntoIter { + self.ptr.into_iter() + } +} + +impl<S: Encoder, T: Encodable<S>> Encodable<S> for P<[T]> { + fn encode(&self, s: &mut S) { + Encodable::encode(&**self, s); + } +} + +impl<D: Decoder, T: Decodable<D>> Decodable<D> for P<[T]> { + fn decode(d: &mut D) -> P<[T]> { + P::from_vec(Decodable::decode(d)) + } +} + +impl<CTX, T> HashStable<CTX> for P<T> +where + T: ?Sized + HashStable<CTX>, +{ + fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) { + (**self).hash_stable(hcx, hasher); + } +} |