feat!: change crossover API & move crossover implementations into separate modules

examples/jssp/problem/crossover.rs

@@ -2,6 +2,7 @@ use ecrs::{
     ga::{individual::IndividualTrait, GAMetadata},
     prelude::crossover::CrossoverOperator,
 };
+use push_trait::PushBack;
 use rand::{thread_rng, Rng};
 
 use super::individual::JsspIndividual;
@@ -16,10 +17,8 @@ impl JsspCrossover {
             distr: rand::distributions::Uniform::new(0.0, 1.0),
         }
     }
-}
 
-impl CrossoverOperator<JsspIndividual> for JsspCrossover {
-    fn apply(
+    fn apply_single(
         &mut self,
         _metadata: &GAMetadata,
         parent_1: &JsspIndividual,
@@ -53,16 +52,30 @@ impl CrossoverOperator<JsspIndividual> for JsspCrossover {
     }
 }
 
+impl CrossoverOperator<JsspIndividual> for JsspCrossover {
+    fn apply(&mut self, metadata: &GAMetadata, selected: &[&JsspIndividual]) -> Vec<JsspIndividual> {
+        assert!(selected.len() & 1 == 0);
+
+        let mut output = Vec::with_capacity(selected.len());
+
+        for parents in selected.chunks(2) {
+            let (child_1, child_2) = self.apply_single(metadata, parents[0], parents[1]);
+            output.push(child_1);
+            output.push(child_2);
+        }
+
+        output
+    }
+}
+
 pub struct NoopCrossover;
 
 impl NoopCrossover {
     pub fn new() -> Self {
         Self
     }
-}
 
-impl CrossoverOperator<JsspIndividual> for NoopCrossover {
-    fn apply(
+    fn apply_single(
         &mut self,
         _metadata: &GAMetadata,
         parent_1: &JsspIndividual,
@@ -71,3 +84,19 @@ impl CrossoverOperator<JsspIndividual> for NoopCrossover {
         (parent_1.clone(), parent_2.clone())
     }
 }
+
+impl CrossoverOperator<JsspIndividual> for NoopCrossover {
+    fn apply(&mut self, metadata: &GAMetadata, selected: &[&JsspIndividual]) -> Vec<JsspIndividual> {
+        assert!(selected.len() & 1 == 0);
+
+        let mut output = Vec::with_capacity(selected.len());
+
+        for parents in selected.chunks(2) {
+            let (child_1, child_2) = self.apply_single(metadata, parents[0], parents[1]);
+            output.push(child_1);
+            output.push(child_2);
+        }
+
+        output
+    }
+}

src/ga.rs

@@ -316,19 +316,9 @@ where
             self.metadata.selection_dur = Some(self.timer.elapsed());
 
             // 5. From mating pool create new generation (apply crossover & mutation).
-            let mut children: Vec<IndividualT> = Vec::with_capacity(self.config.params.population_size);
 
-            // FIXME: Do not assume that population size is an even number.
             self.timer.start();
-            for parents in mating_pool.chunks(2) {
-                let crt_children =
-                    self.config
-                        .crossover_operator
-                        .apply(&self.metadata, parents[0], parents[1]);
-
-                children.push(crt_children.0);
-                children.push(crt_children.1);
-            }
+            let mut children = self.config.crossover_operator.apply(&self.metadata, &mating_pool);
             self.metadata.crossover_dur = Some(self.timer.elapsed());
 
             self.timer.start();

src/ga/operators/crossover.rs

@@ -5,21 +5,32 @@ pub use impls::*;
 
 use crate::ga::individual::IndividualTrait;
 use crate::ga::GAMetadata;
+
 /// # Crossover Operator
 ///
 /// This trait defines common behaviour for crossover operators.
 /// You can implement this trait to provide your custom crossover operator to the GA.
 pub trait CrossoverOperator<IndividualT: IndividualTrait> {
-    /// Returns a tuple of children
+    /// FIXME: Understand lifetimes here!
+    // fn apply_iter<'i, InputIter, OutputIter>(
+    //     &mut self,
+    //     metadata: &GAMetadata,
+    //     selected: InputIter,
+    // ) -> OutputIter
+    // where
+    //     InputIter: Iterator<Item = &'i IndividualT>,
+    //     OutputIter: Iterator<Item = IndividualT>,
+    //     IndividualT: 'i;
+
+    /// Apply crossover operator to the selected population part.
     ///
     /// ## Arguments
     ///
-    /// * `parent_1` - First parent to take part in recombination
-    /// * `parent_2` - Second parent to take part in recombination
-    fn apply(
-        &mut self,
-        metadata: &GAMetadata,
-        parent_1: &IndividualT,
-        parent_2: &IndividualT,
-    ) -> (IndividualT, IndividualT);
+    /// * `metadata` - metadata provided by the GA runtime,
+    /// * `selected` - result of running selection operator,
+    ///
+    /// ## Returns
+    ///
+    /// Vector of individuals created during the crossover stage.
+    fn apply(&mut self, metadata: &GAMetadata, selected: &[&IndividualT]) -> Vec<IndividualT>;
 }