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+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A utility class for implementing "snapshottable" things; a snapshottable data structure permits
+//! you to take a snapshot (via `start_snapshot`) and then, after making some changes, elect either
+//! to rollback to the start of the snapshot or commit those changes.
+//!
+//! This vector is intended to be used as part of an abstraction, not serve as a complete
+//! abstraction on its own. As such, while it will roll back most changes on its own, it also
+//! supports a `get_mut` operation that gives you an arbitrary mutable pointer into the vector. To
+//! ensure that any changes you make this with this pointer are rolled back, you must invoke
+//! `record` to record any changes you make and also supplying a delegate capable of reversing
+//! those changes.
+
+use self::UndoLog::*;
+
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use std::ops;
+
+use undo_log::{Rollback, Snapshots, UndoLogs, VecLog};
+
+#[derive(Debug)]
+pub enum UndoLog<D: SnapshotVecDelegate> {
+ /// New variable with given index was created.
+ NewElem(usize),
+
+ /// Variable with given index was changed *from* the given value.
+ SetElem(usize, D::Value),
+
+ /// Extensible set of actions
+ Other(D::Undo),
+}
+
+impl<D: SnapshotVecDelegate> Rollback<UndoLog<D>> for SnapshotVecStorage<D> {
+ fn reverse(&mut self, undo: UndoLog<D>) {
+ self.values.reverse(undo)
+ }
+}
+impl<D: SnapshotVecDelegate> Rollback<UndoLog<D>> for Vec<D::Value> {
+ fn reverse(&mut self, undo: UndoLog<D>) {
+ match undo {
+ NewElem(i) => {
+ self.pop();
+ assert!(Vec::len(self) == i);
+ }
+
+ SetElem(i, v) => {
+ self[i] = v;
+ }
+
+ Other(u) => {
+ D::reverse(self, u);
+ }
+ }
+ }
+}
+
+pub trait VecLike<D>: AsRef<[D::Value]> + AsMut<[D::Value]> + Rollback<UndoLog<D>>
+where
+ D: SnapshotVecDelegate,
+{
+ fn push(&mut self, item: D::Value);
+ fn len(&self) -> usize;
+ fn reserve(&mut self, size: usize);
+}
+
+impl<D> VecLike<D> for Vec<D::Value>
+where
+ D: SnapshotVecDelegate,
+{
+ fn push(&mut self, item: D::Value) {
+ Vec::push(self, item)
+ }
+ fn len(&self) -> usize {
+ Vec::len(self)
+ }
+ fn reserve(&mut self, size: usize) {
+ Vec::reserve(self, size)
+ }
+}
+
+impl<D> VecLike<D> for &'_ mut Vec<D::Value>
+where
+ D: SnapshotVecDelegate,
+{
+ fn push(&mut self, item: D::Value) {
+ Vec::push(self, item)
+ }
+ fn len(&self) -> usize {
+ Vec::len(self)
+ }
+ fn reserve(&mut self, size: usize) {
+ Vec::reserve(self, size)
+ }
+}
+
+#[allow(type_alias_bounds)]
+pub type SnapshotVecStorage<D: SnapshotVecDelegate> =
+ SnapshotVec<D, Vec<<D as SnapshotVecDelegate>::Value>, ()>;
+
+pub struct SnapshotVec<
+ D: SnapshotVecDelegate,
+ V: VecLike<D> = Vec<<D as SnapshotVecDelegate>::Value>,
+ L = VecLog<UndoLog<D>>,
+> {
+ values: V,
+ undo_log: L,
+ _marker: PhantomData<D>,
+}
+
+impl<D, V, L> fmt::Debug for SnapshotVec<D, V, L>
+where
+ D: SnapshotVecDelegate,
+ V: VecLike<D> + fmt::Debug,
+ L: fmt::Debug,
+{
+ fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+ fmt.debug_struct("SnapshotVec")
+ .field("values", &self.values)
+ .field("undo_log", &self.undo_log)
+ .finish()
+ }
+}
+
+// Snapshots are tokens that should be created/consumed linearly.
+pub struct Snapshot<S = ::undo_log::Snapshot> {
+ pub(crate) value_count: usize,
+ snapshot: S,
+}
+
+pub trait SnapshotVecDelegate {
+ type Value;
+ type Undo;
+
+ fn reverse(values: &mut Vec<Self::Value>, action: Self::Undo);
+}
+
+// HACK(eddyb) manual impl avoids `Default` bound on `D`.
+impl<D: SnapshotVecDelegate, V: VecLike<D> + Default, L: Default> Default for SnapshotVec<D, V, L> {
+ fn default() -> Self {
+ SnapshotVec {
+ values: V::default(),
+ undo_log: Default::default(),
+ _marker: PhantomData,
+ }
+ }
+}
+
+impl<D: SnapshotVecDelegate, V: VecLike<D> + Default, L: Default> SnapshotVec<D, V, L> {
+ /// Creates a new `SnapshotVec`. If `L` is set to `()` then most mutating functions will not
+ /// be accessible without calling `with_log` and supplying a compatibly `UndoLogs` instance.
+ pub fn new() -> Self {
+ Self::default()
+ }
+}
+
+impl<D: SnapshotVecDelegate> SnapshotVecStorage<D> {
+ /// Creates a `SnapshotVec` using the `undo_log`, allowing mutating methods to be called
+ pub fn with_log<'a, L>(
+ &'a mut self,
+ undo_log: L,
+ ) -> SnapshotVec<D, &'a mut Vec<<D as SnapshotVecDelegate>::Value>, L>
+ where
+ L: UndoLogs<UndoLog<D>>,
+ {
+ SnapshotVec {
+ values: &mut self.values,
+ undo_log,
+ _marker: PhantomData,
+ }
+ }
+}
+
+impl<D: SnapshotVecDelegate, L: Default> SnapshotVec<D, Vec<D::Value>, L> {
+ pub fn with_capacity(c: usize) -> Self {
+ SnapshotVec {
+ values: Vec::with_capacity(c),
+ undo_log: Default::default(),
+ _marker: PhantomData,
+ }
+ }
+}
+
+impl<V: VecLike<D>, D: SnapshotVecDelegate, U> SnapshotVec<D, V, U> {
+ pub fn len(&self) -> usize {
+ self.values.len()
+ }
+
+ pub fn get(&self, index: usize) -> &D::Value {
+ &self.values.as_ref()[index]
+ }
+
+ /// Returns a mutable pointer into the vec; whatever changes you make here cannot be undone
+ /// automatically, so you should be sure call `record()` with some sort of suitable undo
+ /// action.
+ pub fn get_mut(&mut self, index: usize) -> &mut D::Value {
+ &mut self.values.as_mut()[index]
+ }
+
+ /// Reserve space for new values, just like an ordinary vec.
+ pub fn reserve(&mut self, additional: usize) {
+ // This is not affected by snapshots or anything.
+ self.values.reserve(additional);
+ }
+}
+
+impl<V: VecLike<D>, D: SnapshotVecDelegate, L: UndoLogs<UndoLog<D>>> SnapshotVec<D, V, L> {
+ fn in_snapshot(&self) -> bool {
+ self.undo_log.in_snapshot()
+ }
+
+ pub fn record(&mut self, action: D::Undo) {
+ if self.in_snapshot() {
+ self.undo_log.push(Other(action));
+ }
+ }
+
+ pub fn push(&mut self, elem: D::Value) -> usize {
+ let len = self.values.len();
+ self.values.push(elem);
+
+ if self.in_snapshot() {
+ self.undo_log.push(NewElem(len));
+ }
+
+ len
+ }
+
+ /// Updates the element at the given index. The old value will saved (and perhaps restored) if
+ /// a snapshot is active.
+ pub fn set(&mut self, index: usize, new_elem: D::Value) {
+ let old_elem = mem::replace(&mut self.values.as_mut()[index], new_elem);
+ if self.undo_log.in_snapshot() {
+ self.undo_log.push(SetElem(index, old_elem));
+ }
+ }
+
+ /// Updates all elements. Potentially more efficient -- but
+ /// otherwise equivalent to -- invoking `set` for each element.
+ pub fn set_all(&mut self, mut new_elems: impl FnMut(usize) -> D::Value) {
+ if !self.undo_log.in_snapshot() {
+ for (index, slot) in self.values.as_mut().iter_mut().enumerate() {
+ *slot = new_elems(index);
+ }
+ } else {
+ for i in 0..self.values.len() {
+ self.set(i, new_elems(i));
+ }
+ }
+ }
+
+ pub fn update<OP>(&mut self, index: usize, op: OP)
+ where
+ OP: FnOnce(&mut D::Value),
+ D::Value: Clone,
+ {
+ if self.undo_log.in_snapshot() {
+ let old_elem = self.values.as_mut()[index].clone();
+ self.undo_log.push(SetElem(index, old_elem));
+ }
+ op(&mut self.values.as_mut()[index]);
+ }
+}
+
+impl<D, V, L> SnapshotVec<D, V, L>
+where
+ D: SnapshotVecDelegate,
+ V: VecLike<D> + Rollback<UndoLog<D>>,
+ L: Snapshots<UndoLog<D>>,
+{
+ pub fn start_snapshot(&mut self) -> Snapshot<L::Snapshot> {
+ Snapshot {
+ value_count: self.values.len(),
+ snapshot: self.undo_log.start_snapshot(),
+ }
+ }
+
+ pub fn actions_since_snapshot(&self, snapshot: &Snapshot<L::Snapshot>) -> &[UndoLog<D>] {
+ self.undo_log.actions_since_snapshot(&snapshot.snapshot)
+ }
+
+ pub fn rollback_to(&mut self, snapshot: Snapshot<L::Snapshot>) {
+ let values = &mut self.values;
+ self.undo_log.rollback_to(|| values, snapshot.snapshot);
+ }
+
+ /// Commits all changes since the last snapshot. Of course, they
+ /// can still be undone if there is a snapshot further out.
+ pub fn commit(&mut self, snapshot: Snapshot<L::Snapshot>) {
+ self.undo_log.commit(snapshot.snapshot);
+ }
+}
+
+impl<D: SnapshotVecDelegate, V: VecLike<D>, L> ops::Deref for SnapshotVec<D, V, L> {
+ type Target = [D::Value];
+ fn deref(&self) -> &[D::Value] {
+ self.values.as_ref()
+ }
+}
+
+impl<D: SnapshotVecDelegate, V: VecLike<D>, L> ops::DerefMut for SnapshotVec<D, V, L> {
+ fn deref_mut(&mut self) -> &mut [D::Value] {
+ self.values.as_mut()
+ }
+}
+
+impl<D: SnapshotVecDelegate, V: VecLike<D>, L> ops::Index<usize> for SnapshotVec<D, V, L> {
+ type Output = D::Value;
+ fn index(&self, index: usize) -> &D::Value {
+ self.get(index)
+ }
+}
+
+impl<D: SnapshotVecDelegate, V: VecLike<D>, L> ops::IndexMut<usize> for SnapshotVec<D, V, L> {
+ fn index_mut(&mut self, index: usize) -> &mut D::Value {
+ self.get_mut(index)
+ }
+}
+
+impl<D: SnapshotVecDelegate, V: VecLike<D> + Extend<D::Value>> Extend<D::Value>
+ for SnapshotVec<D, V>
+{
+ fn extend<T>(&mut self, iterable: T)
+ where
+ T: IntoIterator<Item = D::Value>,
+ {
+ let initial_len = self.values.len();
+ self.values.extend(iterable);
+ let final_len = self.values.len();
+
+ if self.in_snapshot() {
+ self.undo_log
+ .extend((initial_len..final_len).map(|len| NewElem(len)));
+ }
+ }
+}
+
+impl<D: SnapshotVecDelegate, V, L> Clone for SnapshotVec<D, V, L>
+where
+ V: VecLike<D> + Clone,
+ L: Clone,
+{
+ fn clone(&self) -> Self {
+ SnapshotVec {
+ values: self.values.clone(),
+ undo_log: self.undo_log.clone(),
+ _marker: PhantomData,
+ }
+ }
+}
+
+impl<D: SnapshotVecDelegate> Clone for UndoLog<D>
+where
+ D::Value: Clone,
+ D::Undo: Clone,
+{
+ fn clone(&self) -> Self {
+ match *self {
+ NewElem(i) => NewElem(i),
+ SetElem(i, ref v) => SetElem(i, v.clone()),
+ Other(ref u) => Other(u.clone()),
+ }
+ }
+}
+
+impl SnapshotVecDelegate for i32 {
+ type Value = i32;
+ type Undo = ();
+
+ fn reverse(_: &mut Vec<i32>, _: ()) {}
+}
+
+#[test]
+fn basic() {
+ let mut vec: SnapshotVec<i32> = SnapshotVec::default();
+ assert!(!vec.in_snapshot());
+ assert_eq!(vec.len(), 0);
+ vec.push(22);
+ vec.push(33);
+ assert_eq!(vec.len(), 2);
+ assert_eq!(*vec.get(0), 22);
+ assert_eq!(*vec.get(1), 33);
+ vec.set(1, 34);
+ assert_eq!(vec.len(), 2);
+ assert_eq!(*vec.get(0), 22);
+ assert_eq!(*vec.get(1), 34);
+
+ let snapshot = vec.start_snapshot();
+ assert!(vec.in_snapshot());
+
+ vec.push(44);
+ vec.push(55);
+ vec.set(1, 35);
+ assert_eq!(vec.len(), 4);
+ assert_eq!(*vec.get(0), 22);
+ assert_eq!(*vec.get(1), 35);
+ assert_eq!(*vec.get(2), 44);
+ assert_eq!(*vec.get(3), 55);
+
+ vec.rollback_to(snapshot);
+ assert!(!vec.in_snapshot());
+
+ assert_eq!(vec.len(), 2);
+ assert_eq!(*vec.get(0), 22);
+ assert_eq!(*vec.get(1), 34);
+}
+
+#[test]
+#[should_panic]
+fn out_of_order() {
+ let mut vec: SnapshotVec<i32> = SnapshotVec::default();
+ vec.push(22);
+ let snapshot1 = vec.start_snapshot();
+ vec.push(33);
+ let snapshot2 = vec.start_snapshot();
+ vec.push(44);
+ vec.rollback_to(snapshot1); // bogus, but accepted
+ vec.rollback_to(snapshot2); // asserts
+}
+
+#[test]
+fn nested_commit_then_rollback() {
+ let mut vec: SnapshotVec<i32> = SnapshotVec::default();
+ vec.push(22);
+ let snapshot1 = vec.start_snapshot();
+ let snapshot2 = vec.start_snapshot();
+ vec.set(0, 23);
+ vec.commit(snapshot2);
+ assert_eq!(*vec.get(0), 23);
+ vec.rollback_to(snapshot1);
+ assert_eq!(*vec.get(0), 22);
+}
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