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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 https://mozilla.org/MPL/2.0/. * * Copyright 2019 Nathan West */ #![cfg_attr(not(test), no_std)] //! Generations is a utility library for running generation-based simulations, //! such as [Conway's Game of Life](https://www.wikiwand.com/en/Conway%27s_Game_of_Life), //! other [cellular automata](https://www.wikiwand.com/en/Elementary_cellular_automaton), //! and [genetic algorithms](https://www.wikiwand.com/en/Genetic_algorithm). Its //! purpose is to make it unnecessary to allocate new model structures with //! each generation; instead, two generations instances are stored in a //! [`Generations`] struct, one of which is always considered the visible "current" //! generation. //! //! # Example //! //! In this example, our system is an array of integers. With each subsequent //! generation, the values in the array are the sum of the original value and //! its two neighbors. For simplicity, we ignore the first and last element. //! //! For example: //! //! ```text //! [0 1 0 1 1 -1 -1 0] //! [0 1 2 2 1 -1 -2 0] //! [0 3 5 5 2 -2 -3 0] //! [0 8 13 12 5 -3 -5 0] //! [0 21 33 30 14 -3 -8 0] //! ``` //! ``` //! use generations::Generations; //! //! // Our model type is a vector. //! let initial_state = vec![0, 1, 0, 1, 1, -1, -1, 0]; //! //! // A Generations instance stores our model, plus some scratch space to //! // use as the next generation each step. When stepped, the new generation is //! // written to this scratch space, which then becomes the current generation //! // while the previous generation becomes the new scratch space. //! let gens = Generations::new_defaulted(initial_state); //! //! // A Simulation combines a Generations instance with a rule to apply with //! // each step of the simulation //! let mut sim = gens.with_rule(move |current_gen, next_gen| { //! // Make sure to reset the `next_gen` to a blank state before continuing //! next_gen.clear(); //! //! if let Some(&first) = current_gen.first() { //! next_gen.push(first); //! } //! //! for window in current_gen.windows(3) { //! next_gen.push(window[0] + window[1] + window[2]); //! } //! //! if current_gen.len() > 1 { //! next_gen.push(*current_gen.last().unwrap()) //! } //! }); //! //! assert_eq!(sim.current(), &[0, 1, 0, 1, 1, -1, -1, 0]); //! sim.step(); //! assert_eq!(sim.current(), &[0, 1, 2, 2, 1, -1, -2, 0]); //! sim.step(); //! assert_eq!(sim.current(), &[0, 3, 5, 5, 2, -2, -3, 0]); //! sim.step(); //! assert_eq!(sim.current(), &[0, 8, 13, 12, 5, -3, -5, 0]); //! sim.step(); //! assert_eq!(sim.current(), &[0, 21, 33, 30, 14, -3, -8, 0]); //! ``` use core::fmt; use core::mem; /// This struct manages transitions between generations. It stores two models, /// one of which is considered "current" and the other "scratch". The [`step`][Generations::step] /// method advances the simulation by calling a function with a reference to /// the current generation and a mutable reference to the scratch generation; /// the function uses the current generation to write the next generation out /// to the scratch generation, after which it becomes the new current generation /// (and the previous generation becomes the new scratch generation). #[derive(Debug, Clone)] pub struct Generations<Model> { current: Model, scratch: Model, } impl<Model> Generations<Model> { /// Create a new `Generations` instance with a seed model, which will /// become the initial current generation, and a scratch generation. /// /// # Example /// /// Create a simulation using a vector for the seed generation and a /// pre-allocated vector for the scratch generation /// /// ``` /// use generations::Generations; /// /// let mut gen = Generations::new( /// vec![1, 2, 3, 4, 5], /// Vec::with_capacity(5) /// ); /// /// gen.step(|current_gen, next_gen| { /// assert_eq!(current_gen, &[1, 2, 3, 4, 5]); /// assert_eq!(next_gen, &[]); /// assert_eq!(next_gen.capacity(), 5); /// }); /// ``` #[inline] #[must_use] pub fn new(seed: Model, scratch: Model) -> Self { Generations { current: seed, scratch, } } /// Get a reference to the current generation. This is the result of the /// most recent step or reset, or the seed generation if no steps have been /// run. /// /// # Example /// /// ``` /// use generations::Generations; /// /// let gen = Generations::new_defaulted(vec![1, 2, 3, 4]); /// assert_eq!(gen.current(), &[1, 2, 3, 4]); /// ``` #[inline] #[must_use] pub fn current(&self) -> &Model { &self.current } /// Advance the simulation 1 step using a stepping function. The stepping /// function takes a reference to the current generation and a mutable /// reference to the new generation. The stepping function should advance /// the simulation by reading the current genration and writing the next /// generation. After the stepping function writes the new generation, /// it is marked as current. /// /// This function returns a reference to the *previously current* /// generation, so that it can be compared if desired with the current /// generation. /// /// # Example /// /// ``` /// // Simple example that rotates a vector 1 step /// use generations::Generations; /// /// let mut gen = Generations::new_cloned(vec![1, 2, 3, 4]); /// /// let prev = gen.step(|current_gen, next_gen| { /// next_gen.clear(); /// next_gen.extend(current_gen.iter().skip(1)); /// next_gen.extend(current_gen.first()); /// }); /// /// assert_eq!(prev, &[1, 2, 3, 4]); /// assert_eq!(gen.current(), &[2, 3, 4, 1]); /// ``` #[inline] pub fn step(&mut self, stepper: impl FnOnce(&Model, &mut Model)) -> &Model { stepper(&self.current, &mut self.scratch); mem::swap(&mut self.current, &mut self.scratch); &self.scratch } /// Replace the current generation with a new seed generation using a /// function. Has no effect on the existing scratch generation. /// /// ``` /// use generations::Generations; /// /// let mut gen = Generations::new_defaulted(vec![1, 2, 3, 4]); /// gen.reset_with(|seed_gen| { /// seed_gen.clear(); /// seed_gen.extend(&[5, 5, 5, 5]); /// }); /// assert_eq!(gen.current(), &[5, 5, 5, 5]); /// ``` #[inline] pub fn reset_with(&mut self, seeder: impl FnOnce(&mut Model)) { seeder(&mut self.current) } /// Replace the current generation with a new seed generation. Has no /// effect on the existing scratch generation. /// /// See also [`reset_with`][Generations::reset_with] for a reset /// method that reuses the existing storage of the current generation. /// /// ``` /// use generations::Generations; /// /// let mut gen = Generations::new_defaulted(vec![1, 2, 3, 4]); /// gen.reset(vec![4, 3, 2, 1]); /// assert_eq!(gen.current(), &[4, 3, 2, 1]); /// ``` #[inline] pub fn reset(&mut self, seed: Model) { self.current = seed; } /// Combine a `Generations` struct with a repeatable stepping function, to /// create a simulation that can be stepped with the same logic each /// generation. See [`step`][Generations::step] for an explaination of /// the stepping function. #[inline] #[must_use] pub fn with_rule<F: FnMut(&Model, &mut Model)>(self, stepper: F) -> Simulation<Model, F> { Simulation { generations: self, stepper, } } } impl<Model: Clone> Generations<Model> { /// Create a new `Generations` instance with a seed model. Clone the seed /// model to create an initial scratch model. #[inline] #[must_use] pub fn new_cloned(seed_generation: Model) -> Self { let scratch = seed_generation.clone(); Self::new(seed_generation, scratch) } /// Replace the current generation with a clone of a new seed generation. /// Has no effect on the current scratch generation. #[inline] pub fn reset_from(&mut self, seed: &Model) { self.current.clone_from(seed) } } impl<Model: Default> Generations<Model> { /// Create a new `Generations` instance with a seed model. The Model type's /// default value is used as the initial scratch model. #[inline] #[must_use] pub fn new_defaulted(seed_generation: Model) -> Self { Self::new(seed_generation, Model::default()) } } /// A [`Simulation`] is a [`Generations`] instance combined with a stepping /// function. It allows you to repeatedly step through generations, using /// the same logic with each step. /// /// It provides a [`step`][Simulation::step] method, which advances the /// simulaton with the underlying stepper. /// /// It is constructed with the [`Generations::with_rule`] method. #[derive(Clone)] pub struct Simulation<Model, Step> { generations: Generations<Model>, stepper: Step, } impl<Model, Step> Simulation<Model, Step> { /// Return a reference to the current generation, which is the result of /// the most recent step, or the seed generation if no steps have been /// performed. #[inline] #[must_use] pub fn current(&self) -> &Model { self.generations.current() } /// Replace the current generation with a new seed generation using a /// function. Has no effect on the existing scratch generation. The current /// generation is cleared before the seed function is called. #[inline] pub fn reset_with(&mut self, seeder: impl FnOnce(&mut Model)) { self.generations.reset_with(seeder) } /// Replace the current generation with a new seed generation. Has no /// effect on the existing scratch generation. #[inline] pub fn reset(&mut self, seed: Model) { self.generations.reset(seed) } /// Discard the stepping function and return the underlying `Generations` /// instance #[inline] pub fn unwrap(self) -> Generations<Model> { self.generations } } impl<Model: Clone, Step> Simulation<Model, Step> { /// Replace the current generation with a clone of a new seed generation. /// Has no effect on the current scratch generation. #[inline] pub fn reset_from(&mut self, seed: &Model) { self.generations.reset_from(seed) } } impl<Model, Step: FnMut(&Model, &mut Model)> Simulation<Model, Step> { /// Step the simulation using the stored stepping function. Returns a /// reference to the *previously current* generation. #[inline] pub fn step(&mut self) -> &Model { self.generations.step(&mut self.stepper) } } // TODO: default impl this, add a specialization for Step: Debug impl<Model: fmt::Debug, Step> fmt::Debug for Simulation<Model, Step> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("Simulation") .field("generations", &self.generations) .field("stepper", &"<closure>") .finish() } } impl<Model, Step> AsRef<Generations<Model>> for Simulation<Model, Step> { fn as_ref(&self) -> &Generations<Model> { &self.generations } } // TODO: create an iterator. Probably impossible until we get GATs. // Conceivably we could just clone the model at every step of the iteration, // but that would... defeat the entire purpose of the library? unless we wrapped // it all up in an Rc or something. #[cfg(test)] mod tests { use crate::Generations; #[test] fn basic_test() { // This test checks essentially all of the functionality of the library. // individual methods not covered here are covered by doctests. // For these tests, the model that we're using is a vector, where in // each generation, the new value is the sum of the old value and its // neighbors. For instance: // // [1 0 1 1 -1 -1] // [1 2 2 1 -1 -2] // [3 5 5 2 -2 -3] // [8 13 12 5 -3 -5] // [21 33 30 14 -3 -8] // // For simplicity of implementation of bounds checking, we use a vector // bounded by zeroes to make this work let gen = Generations::new(vec![0, 1, 0, 1, 1, -1, -1, 0], vec![]); let mut gen = gen.with_rule(|current_gen, next_gen| { next_gen.clear(); next_gen.push(0); for window in current_gen.windows(3) { next_gen.push(window[0] + window[1] + window[2]); } next_gen.push(0); }); assert_eq!(gen.current(), &[0, 1, 0, 1, 1, -1, -1, 0]); gen.step(); assert_eq!(gen.current(), &[0, 1, 2, 2, 1, -1, -2, 0]); gen.step(); assert_eq!(gen.current(), &[0, 3, 5, 5, 2, -2, -3, 0]); gen.step(); assert_eq!(gen.current(), &[0, 8, 13, 12, 5, -3, -5, 0]); gen.step(); assert_eq!(gen.current(), &[0, 21, 33, 30, 14, -3, -8, 0]); // TODO: find a way to test that no reallocations are happening } #[test] fn debug_print_test() { // Simulations should be debug-printable when created with a closure let thing = Generations::new_defaulted(vec![0]).with_rule(|_c, _n| {}); format!("{:?}", &thing); } }