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/* * This Source Code Form is subject to the terms of the Mozilla Public License, * v. 2.0. If a copy of the MPL was not distributed with this file, You can * obtain one at http://mozilla.org/MPL/2.0/. */ //! Simple state restoration for backtracking search algorithms using a trail. //! //! During a typical branching search algorithm, the search state must be cloned at each branch //! point in order to explore the branches independently. `contrail` provides a framework to create //! search algorithms that only require a partial clone of the search state at each branch point. //! This is facilitated by the [_trail_](Trail), a struct where all search state is stored. //! //! This library is based on the memory model used by //! [Minion](https://constraintmodelling.org/minion/), a C++ constraint satisfaction problem //! solver. //! //! # Limitations //! //! The main limitation of contrail is that once a trail has been created using a trail builder, //! nothing can be added to the trail. This is to prevent dangling pointers. #[allow(unused_imports)] #[macro_use] extern crate contrail_derive; #[doc(hidden)] pub use contrail_derive::*; pub mod mem; pub mod storage; use std::{fmt, marker::PhantomData}; use crate::{ mem::{ArrayPointer, Bytes, Memory, MemoryBuilder, Pointer}, storage::{Backtrackable, NonBacktrackable, StorageMode}, }; /// The trail itself. /// /// # Backtrackable and non-backtrackable memory /// /// The trail consists of [_backtrackable_](storage::Backtrackable) memory and /// [_non-backtrackable_](storage::NonBacktrackable) memory. Both types of storage can be used with /// [`Value`](Value) and [`Array`](Array). Whenever `trail.new_level()` is called, a clone of the /// backtrackable memory is made and appended to an internal stack. Conversely, whenever /// `trail.backtrack()` is called, the current backtrackable memory is replaced with the most /// recent clone from the internal stack. Non-backtrackable memory is unaffected by these methods. /// /// When designing data structures using the trail, try to store as much as possible in /// non-backtrackable storage. This will make calls to `new_level()` and `backtrack()` more /// efficient as less data will need to be cloned. /// /// # Examples /// /// The following example illustrates the differences between `Backtrackable` and /// `NonBacktrackable` storage: /// /// ``` /// use contrail::{BacktrackableValue, NonBacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let backtrackable_counter = BacktrackableValue::new(&mut builder, 0); /// let non_backtrackable_counter = NonBacktrackableValue::new(&mut builder, 0); /// let mut trail = builder.finish(); /// /// assert_eq!(backtrackable_counter.get(&trail), 0); /// assert_eq!(non_backtrackable_counter.get(&trail), 0); /// /// trail.new_level(); /// /// backtrackable_counter.update(&mut trail, |x| x + 1); /// non_backtrackable_counter.update(&mut trail, |x| x + 1); /// /// assert_eq!(backtrackable_counter.get(&trail), 1); /// assert_eq!(non_backtrackable_counter.get(&trail), 1); /// /// trail.backtrack(); /// /// assert_eq!(backtrackable_counter.get(&trail), 0); /// assert_eq!(non_backtrackable_counter.get(&trail), 1); /// ``` /// /// Another example that backtracks multiple times: /// /// ``` /// use contrail::{BacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let countdown = BacktrackableValue::new(&mut builder, 3); /// let mut trail = builder.finish(); /// /// println!("Counting down from {}:", countdown.get(&trail)); /// /// while countdown.get(&trail) > 0 { /// trail.new_level(); /// println!("{}...", countdown.get(&trail)); /// countdown.update(&mut trail, |x| x - 1); /// } /// /// println!("{}!", countdown.get(&trail)); /// /// println!("Counting back up:"); /// /// while !trail.is_trail_empty() { /// trail.backtrack(); /// println!("{}", countdown.get(&trail)); /// } /// ``` /// /// This produces the following output: /// /// ```txt /// Counting down from 3: /// 3... /// 2... /// 1... /// 0! /// Counting back up: /// 1 /// 2 /// 3 /// ``` pub struct Trail { backtrackable_mem: Memory, non_backtrackable_mem: Memory, trail: Vec<Memory>, } impl Trail { /// Adds a new level to the trail. /// /// When this method is called, a clone of the trail's backtrackable memory at that point in /// time is added to an internal stack of memory. These memory snapshots can be recalled in /// FILO order using [`backtrack()`](Trail::backtrack). /// /// # Examples /// /// ``` /// use contrail::{BacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let value = BacktrackableValue::new(&mut builder, 0); /// let mut trail = builder.finish(); /// /// value.set(&mut trail, 1); /// trail.new_level(); /// value.set(&mut trail, 2); /// trail.backtrack(); /// assert_eq!(value.get(&trail), 1); /// ``` pub fn new_level(&mut self) { self.trail.push(self.backtrackable_mem.clone()); } /// Backtracks the trail to the most recent level. /// /// When this method is called, the most recent backtrackable memory stored in the trail's /// internal stack is removed from the stack and set as the current backtrackable memory. If /// the trail is empty, this method has no effect. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let value = BacktrackableValue::new(&mut builder, 0); /// let mut trail = builder.finish(); /// /// value.set(&mut trail, 1); /// trail.new_level(); /// value.set(&mut trail, 2); /// trail.backtrack(); /// assert_eq!(value.get(&trail), 1); /// ``` pub fn backtrack(&mut self) { if let Some(prev) = self.trail.pop() { self.backtrackable_mem = prev; } } /// Returns the length of the trail. /// /// The length of the trail is increased whenever a level is added, and decreased whenever a /// backtrack occurs. /// /// # Examples /// /// ``` /// use contrail::TrailBuilder; /// /// let mut trail = TrailBuilder::new().finish(); /// /// assert_eq!(trail.trail_len(), 0); /// /// trail.new_level(); /// assert_eq!(trail.trail_len(), 1); /// /// trail.backtrack(); /// assert_eq!(trail.trail_len(), 0); /// ``` pub fn trail_len(&self) -> usize { self.trail.len() } /// Checks if the trail's length is 0. /// /// # Examples /// /// ``` /// use contrail::TrailBuilder; /// /// let mut trail = TrailBuilder::new().finish(); /// /// assert!(trail.is_trail_empty()); /// /// trail.new_level(); /// assert!(!trail.is_trail_empty()); /// /// trail.backtrack(); /// assert!(trail.is_trail_empty()); /// ``` pub fn is_trail_empty(&self) -> bool { self.trail.is_empty() } } /// A builder to create a `Trail`. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let value = BacktrackableValue::new(&mut builder, 5); /// let trail = builder.finish(); /// /// assert_eq!(value.get(&trail), 5); /// ``` #[derive(Debug, Default)] pub struct TrailBuilder { backtrackable_mem: MemoryBuilder, non_backtrackable_mem: MemoryBuilder, } impl TrailBuilder { /// Creates a new empty `TrailBuilder`. /// /// # Examples /// /// ``` /// use contrail::TrailBuilder; /// /// let mut builder = TrailBuilder::new(); /// ``` pub fn new() -> Self { Self { backtrackable_mem: MemoryBuilder::new(), non_backtrackable_mem: MemoryBuilder::new(), } } /// Consumes the `TrailBuilder` to create a new `Trail`. /// /// Once this method is called, any `Value` and `Array` that were created using the /// `TrailBuilder` are usable with the resulting `Trail`. /// /// # Examples /// /// ``` /// use contrail::{NonBacktrackableArray, NonBacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let value = NonBacktrackableValue::new(&mut builder, -123); /// let array = NonBacktrackableArray::new(&mut builder, vec![1, 3, 5, 7]); /// let trail = builder.finish(); /// /// assert_eq!(value.get(&trail), -123); /// assert_eq!(array.get(&trail, 2), 5); /// ``` pub fn finish(self) -> Trail { Trail { backtrackable_mem: self.backtrackable_mem.finish(), non_backtrackable_mem: self.non_backtrackable_mem.finish(), trail: vec![], } } } /// A reference to a value stored on the trail. /// /// The type parameter `T` is the type of value stored on the trail, and the type parameter `M` /// represents how the value is stored on the trail. A `Value<Backtrackable, T>` is stored on the /// trail in backtrackable memory, whereas a `Value<NonBacktrackable, T>` is stored on the trail in /// non-backtrackable memory. /// /// Instead of using `Value` directly, it's often easier to use the type definitions /// [`BacktrackableValue`](BacktrackableValue) and [`NonBacktrackableValue`](NonBacktrackableValue). pub struct Value<M, T> { pointer: Pointer<T>, phantom: PhantomData<M>, } impl<M, T> Value<M, T> where M: StorageMode, T: Bytes, { /// Creates a new `Value` with the given value. /// /// The `Value` is usable after the `TrailBuilder` used to create it is finished. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let value = BacktrackableValue::new(&mut builder, 'b'); /// let trail = builder.finish(); /// /// // the value is usable now /// assert_eq!(value.get(&trail), 'b'); /// ``` pub fn new(builder: &mut TrailBuilder, val: T) -> Self { Self { pointer: Pointer::new(M::builder_mut(builder), val), phantom: PhantomData, } } /// Gets the value from the trail. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let value = BacktrackableValue::new(&mut builder, 5); /// let mut trail = builder.finish(); /// /// assert_eq!(value.get(&trail), 5); /// ``` #[inline] pub fn get(self, trail: &Trail) -> T { self.pointer.get(M::memory(trail)) } /// Sets the value on the trail. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let value = BacktrackableValue::new(&mut builder, 5); /// let mut trail = builder.finish(); /// /// value.set(&mut trail, 42); /// assert_eq!(value.get(&trail), 42); /// ``` #[inline] pub fn set(self, trail: &mut Trail, new_val: T) { self.pointer.set(M::memory_mut(trail), new_val); } /// Updates the value on the trail using the given function. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableValue, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let value = BacktrackableValue::new(&mut builder, 5); /// let mut trail = builder.finish(); /// /// value.update(&mut trail, |x| x * x); /// assert_eq!(value.get(&trail), 25); /// ``` #[inline] pub fn update(self, trail: &mut Trail, f: impl FnOnce(T) -> T) { self.pointer.update(M::memory_mut(trail), f); } } impl<M, T> Clone for Value<M, T> { fn clone(&self) -> Self { Self { pointer: self.pointer, phantom: PhantomData, } } } impl<M, T> Copy for Value<M, T> {} impl<M, T> fmt::Debug for Value<M, T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("Value") .field("pointer", &self.pointer) .finish() } } impl<M, T> Eq for Value<M, T> {} impl<M, T> PartialEq for Value<M, T> { fn eq(&self, other: &Self) -> bool { self.pointer == other.pointer } } /// A reference to a fixed-length array of values stored on the trail. /// /// The type parameter `T` is the type of value stored on the trail, and the type parameter `M` /// represents how the value is stored on the trail. An `Array<Backtrackable, T>` is stored on the /// trail in backtrackable memory, whereas an `Array<NonBacktrackable, T>` is stored on the trail /// in non-backtrackable memory. /// /// Instead of using `Array` directly, it's often easier to use the type definitions /// [`BacktrackableArray`](BacktrackableArray) and /// [`NonBacktrackableArray`](NonBacktrackableArray). pub struct Array<M, T> { pointer: ArrayPointer<T>, phantom: PhantomData<M>, } impl<M, T> Array<M, T> where M: StorageMode, T: Bytes, { /// Creates a new `Array` with the given values. /// /// The `Array` is usable after the `TrailBuilder` used to create it is finished. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableArray, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let array = BacktrackableArray::new(&mut builder, 5..10); /// let trail = builder.finish(); /// /// // the array is usable now /// assert_eq!(array.get(&trail, 2), 7); /// ``` pub fn new(builder: &mut TrailBuilder, vals: impl IntoIterator<Item = T>) -> Self { Self { pointer: ArrayPointer::new( M::builder_mut(builder), &vals.into_iter().collect::<Vec<_>>(), ), phantom: PhantomData, } } /// Returns the length of the array. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableArray, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let array = BacktrackableArray::new(&mut builder, 0..8); /// /// assert_eq!(array.len(), 8); /// ``` #[inline] pub fn len(&self) -> usize { self.pointer.len() } /// Checks if the length of the array is equal to 0. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableArray, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let empty = BacktrackableArray::new(&mut builder, 0..0); /// let not_empty = BacktrackableArray::new(&mut builder, 0..1); /// /// assert_eq!(empty.is_empty(), true); /// assert_eq!(not_empty.is_empty(), false); /// ``` #[inline] pub fn is_empty(&self) -> bool { self.pointer.len() == 0 } /// Returns an iterator over the elements of the array. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableArray, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let odds = BacktrackableArray::new(&mut builder, (0..10).map(|x| 2 * x + 1)); /// let trail = builder.finish(); /// /// for odd in odds.iter(&trail) { /// assert_eq!(odd % 2, 1); /// } /// ``` pub fn iter<'t>(&self, trail: &'t Trail) -> ArrayIter<'t, M, T> { ArrayIter { trail, index: 0, array: *self, } } /// Gets the value of the array at the given index. /// /// # Panics /// /// Panics if the index is out of bounds. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableArray, Trail, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let array = BacktrackableArray::new(&mut builder, 0..10); /// let mut trail = builder.finish(); /// /// assert_eq!(array.get(&trail, 4), 4); /// ``` #[inline] pub fn get(&self, trail: &Trail, i: usize) -> T { self.pointer.get(M::memory(trail), i) } /// Sets the value of the array at the given index. /// /// # Panics /// /// Panics if the index is out of bounds. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableArray, Trail, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let array = BacktrackableArray::new(&mut builder, 0..10); /// let mut trail = builder.finish(); /// /// assert_eq!(array.get(&trail, 4), 4); /// /// array.set(&mut trail, 4, -23); /// assert_eq!(array.get(&trail, 4), -23); /// ``` #[inline] pub fn set(&self, trail: &mut Trail, i: usize, new_val: T) { self.pointer.set(M::memory_mut(trail), i, new_val); } /// Updates the value of the array at the given index using the given update function. /// /// # Panics /// /// Panics if the index is out of bounds. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableArray, Trail, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let array = BacktrackableArray::new(&mut builder, 0..10); /// let mut trail = builder.finish(); /// /// assert_eq!(array.get(&trail, 4), 4); /// /// array.update(&mut trail, 4, |x| x * x); /// assert_eq!(array.get(&trail, 4), 16); /// ``` #[inline] pub fn update(&self, trail: &mut Trail, i: usize, f: impl FnOnce(T) -> T) { self.pointer.update(M::memory_mut(trail), i, f); } /// Swaps the two values at the given indices of the array in memory. /// /// # Panics /// /// Panics if either of the indices are out of bounds. /// /// # Examples /// /// ``` /// use contrail::{BacktrackableArray, TrailBuilder}; /// /// let mut builder = TrailBuilder::new(); /// let array = BacktrackableArray::new(&mut builder, vec!['r', 'u', 't', 's']); /// let mut trail = builder.finish(); /// /// assert_eq!(array.get(&trail, 2), 't'); /// assert_eq!(array.get(&trail, 3), 's'); /// /// array.swap(&mut trail, 2, 3); /// /// assert_eq!(array.get(&trail, 2), 's'); /// assert_eq!(array.get(&trail, 3), 't'); /// ``` #[inline] pub fn swap(&self, trail: &mut Trail, i: usize, j: usize) { self.pointer.swap(M::memory_mut(trail), i, j); } } impl<M, T> Clone for Array<M, T> { fn clone(&self) -> Self { Self { pointer: self.pointer, phantom: PhantomData, } } } impl<M, T> Copy for Array<M, T> {} impl<M, T> fmt::Debug for Array<M, T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("Array") .field("pointer", &self.pointer) .finish() } } impl<M, T> Eq for Array<M, T> {} impl<M, T> PartialEq for Array<M, T> { fn eq(&self, other: &Self) -> bool { self.pointer == other.pointer } } /// An iterator over the values of an `Array`. pub struct ArrayIter<'t, M, T> { trail: &'t Trail, index: usize, array: Array<M, T>, } impl<'t, M, T> Iterator for ArrayIter<'t, M, T> where M: StorageMode, T: Bytes, { type Item = T; fn next(&mut self) -> Option<T> { if self.index == self.array.len() { None } else { let to_ret = Some(self.array.get(self.trail, self.index)); self.index += 1; to_ret } } } /// A value stored on the trail in backtrackable memory. pub type BacktrackableValue<T> = Value<Backtrackable, T>; /// A value stored on the trail in non-backtrackable memory. pub type NonBacktrackableValue<T> = Value<NonBacktrackable, T>; /// A fixed-length array stored on the trail in backtrackable memory. pub type BacktrackableArray<T> = Array<Backtrackable, T>; /// A fixed-length array stored on the trail in non-backtrackable memory. pub type NonBacktrackableArray<T> = Array<NonBacktrackable, T>; #[cfg(test)] mod tests { use super::*; mod value { use super::*; #[test] fn debug() { let mut builder = TrailBuilder::new(); let value = BacktrackableValue::new(&mut builder, 42); assert_eq!( format!("{:?}", value), "Value { pointer: Pointer { offset: 0 } }" ); } #[test] fn clone_eq() { let mut builder = TrailBuilder::new(); let value = BacktrackableValue::new(&mut builder, -1); assert_eq!(value, value.clone()); } #[test] fn get_set_roundtrip() { let init_val = 5; let new_val = 6; let mut builder = TrailBuilder::new(); let backtrackable = BacktrackableValue::new(&mut builder, init_val); let non_backtrackable = NonBacktrackableValue::new(&mut builder, init_val); let mut trail = builder.finish(); assert_eq!(trail.trail_len(), 0); assert!(trail.is_trail_empty()); assert_eq!(backtrackable.get(&trail), init_val); assert_eq!(non_backtrackable.get(&trail), init_val); trail.new_level(); assert_eq!(trail.trail_len(), 1); assert!(!trail.is_trail_empty()); assert_eq!(backtrackable.get(&trail), init_val); assert_eq!(non_backtrackable.get(&trail), init_val); backtrackable.set(&mut trail, new_val); non_backtrackable.set(&mut trail, new_val); assert_eq!(backtrackable.get(&trail), new_val); assert_eq!(non_backtrackable.get(&trail), new_val); trail.backtrack(); assert_eq!(trail.trail_len(), 0); assert!(trail.is_trail_empty()); assert_eq!(backtrackable.get(&trail), init_val); assert_eq!(non_backtrackable.get(&trail), new_val); } #[test] fn update() { let mut builder = TrailBuilder::new(); let value = BacktrackableValue::new(&mut builder, 0); let mut trail = builder.finish(); assert_eq!(value.get(&trail), 0); value.update(&mut trail, |x| x + 1); assert_eq!(value.get(&trail), 1); } } mod array { use super::*; #[test] fn debug() { let mut builder = TrailBuilder::new(); let array = BacktrackableArray::new(&mut builder, vec![1, 2, 3, 4]); assert_eq!( format!("{:?}", array), "Array { pointer: ArrayPointer { offset: 0, len: 4 } }" ); } #[test] fn clone_eq() { let mut builder = TrailBuilder::new(); let array = BacktrackableArray::new(&mut builder, 0..10); assert_eq!(array, array.clone()); } #[test] fn get_set_roundtrip() { let init_vals = vec![1, 3, 5, 7]; let new_vals = vec![2, 4, 6, 8]; let mut builder = TrailBuilder::new(); let backtrackable = BacktrackableArray::new(&mut builder, init_vals.clone()); let stored = NonBacktrackableArray::new(&mut builder, init_vals.clone()); let mut trail = builder.finish(); assert_eq!(trail.trail_len(), 0); assert!(trail.is_trail_empty()); for i in 0..4 { assert_eq!(backtrackable.get(&trail, i), init_vals[i]); assert_eq!(stored.get(&trail, i), init_vals[i]); trail.new_level(); assert_eq!(trail.trail_len(), 1); assert!(!trail.is_trail_empty()); assert_eq!(backtrackable.get(&trail, i), init_vals[i]); assert_eq!(stored.get(&trail, i), init_vals[i]); backtrackable.set(&mut trail, i, new_vals[i]); stored.set(&mut trail, i, new_vals[i]); assert_eq!(backtrackable.get(&trail, i), new_vals[i]); assert_eq!(stored.get(&trail, i), new_vals[i]); trail.backtrack(); assert_eq!(trail.trail_len(), 0); assert!(trail.is_trail_empty()); assert_eq!(backtrackable.get(&trail, i), init_vals[i]); assert_eq!(stored.get(&trail, i), new_vals[i]); } } #[test] fn update() { let mut builder = TrailBuilder::new(); let array = BacktrackableArray::new(&mut builder, 0..10); let mut trail = builder.finish(); assert_eq!(array.get(&trail, 5), 5); array.update(&mut trail, 5, |x| x * 2); assert_eq!(array.get(&trail, 5), 10); } #[test] fn iter() { let vals = vec![1, 3, 5, 7, 9]; let mut builder = TrailBuilder::new(); let array = BacktrackableArray::new(&mut builder, vals.clone()); let trail = builder.finish(); let iter_vals = array.iter(&trail).collect::<Vec<_>>(); assert_eq!(iter_vals, vals); } #[test] fn empty() { let mut builder = TrailBuilder::new(); let empty = BacktrackableArray::new(&mut builder, 0..0); let not_empty = BacktrackableArray::new(&mut builder, 0..1); assert_eq!(empty.len(), 0); assert!(empty.is_empty()); assert_eq!(not_empty.len(), 1); assert!(!not_empty.is_empty()); } #[test] fn swap() { let mut builder = TrailBuilder::new(); let array = BacktrackableArray::new(&mut builder, vec![-1, 1]); let mut trail = builder.finish(); assert_eq!(array.get(&mut trail, 0), -1); assert_eq!(array.get(&mut trail, 1), 1); array.swap(&mut trail, 0, 1); assert_eq!(array.get(&mut trail, 0), 1); assert_eq!(array.get(&mut trail, 1), -1); } } }