summaryrefslogtreecommitdiffstats
path: root/compiler/rustc_ast/src/ptr.rs
blob: 4b2850336a03db2479ec59804de725eb26ff23ae (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
//! 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::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);
    }
}