simplify the inteface of the metric classes

docs/metrics.md

@@ -64,20 +64,14 @@ are intended to be used for multi-objective optimization problems.
 
 If you want to track something that doesn't have a metric already implemented 
 for it, it's possible to implement your own metrics. Metrics must be derived
-from the `Monitor` class, and implement 3 methods: `initialize`, `update`, and
-`value_at`:
+from the `Monitor` class, and implement the `initialize`, and `update` methods:
 
 ```cpp
 // The second type parameter of Monitor is the type used to store the
 // gathered metrics. This will be used as the type of the data_ field.
 class MyMetric : public metrics::Monitor<MyMetric, std::vector<double>>
 {
-public:
-    // Returns the value of the metric in the given generation.
-    // Note that this method is not virtual.
-    double value_at(size_t generation) const noexcept { return data_[generation]; }
-private:
-    // Initialize the metric. Called at the start of a run.
+    // (optional) Initialize the metric. Called at the start of a run.
     void initialize(const GaInfo& ga) override { data_.clear(); }
 
     // Update the metric with a new value from the current generation.

examples/9_metrics.cpp

@@ -10,8 +10,6 @@ using namespace gapp;
 
 struct MyMetric : public metrics::Monitor<MyMetric, std::vector<double>>
 {
-    double value_at(size_t generation) const noexcept { return data_[generation]; }
-    void initialize(const GaInfo&) override { data_.clear(); }
     void update(const GaInfo& ga) override { data_.push_back(ga.fitness_matrix()[0][0]); }
 };
 

src/metrics/distribution_metrics.cpp

@@ -13,13 +13,6 @@ namespace gapp::metrics
 {
     using math::Point;
 
-    std::span<const double> NadirPoint::value_at(size_t generation) const noexcept
-    {
-        GAPP_ASSERT(generation < data_.size());
-
-        return data_[generation];
-    }
-
     void NadirPoint::initialize(const GaInfo& ga)
     {
         data_.clear();
@@ -39,13 +32,6 @@ namespace gapp::metrics
         ref_point_(std::move(ref_point))
     {}
 
-    double Hypervolume::value_at(size_t generation) const noexcept
-    {
-        GAPP_ASSERT(generation < data_.size());
-
-        return data_[generation];
-    }
-
     void Hypervolume::initialize(const GaInfo& ga)
     {
         GAPP_ASSERT(ref_point_.size() == ga.num_objectives());
@@ -63,13 +49,6 @@ namespace gapp::metrics
     }
 
 
-    double AutoHypervolume::value_at(size_t generation) const noexcept
-    {
-        GAPP_ASSERT(generation < data_.size());
-
-        return data_[generation];
-    }
-
     void AutoHypervolume::initialize(const GaInfo& ga)
     {
         data_.clear();

src/metrics/distribution_metrics.hpp

@@ -16,9 +16,6 @@ namespace gapp::metrics
     */
     class NadirPoint final : public Monitor<NadirPoint, FitnessMatrix>
     {
-    public:
-        std::span<const double> value_at(size_t generation) const noexcept;
-    private:
         void initialize(const GaInfo& ga) override;
         void update(const GaInfo& ga) override;
     };
@@ -50,8 +47,6 @@ namespace gapp::metrics
         /** @returns The reference point used for computing the hypervolumes. */
         const FitnessVector& ref_point() const noexcept { return ref_point_; }
 
-        double value_at(size_t generation) const noexcept;
-
     private:
         void initialize(const GaInfo& ga) override;
         void update(const GaInfo& ga) override;
@@ -79,7 +74,6 @@ namespace gapp::metrics
         /** @returns The reference point used for computing the hypervolumes. */
         const FitnessVector& ref_point() const noexcept { return worst_point_; }
 
-        double value_at(size_t generation) const noexcept;
     private:
         void initialize(const GaInfo& ga) override;
         void update(const GaInfo& ga) override;

src/metrics/fitness_metrics.hpp

@@ -16,13 +16,6 @@ namespace gapp::metrics
     template<typename Derived>
     class FitnessMonitor : public Monitor<Derived, FitnessMatrix>
     {
-    public:
-        std::span<const double> value_at(size_t generation) const noexcept
-        {
-            GAPP_ASSERT(generation < this->data_.size());
-
-            return this->data_[generation];
-        }
     private:
         void initialize(const GaInfo& ga) override
         {

src/metrics/metric_set.hpp

@@ -51,7 +51,7 @@ namespace gapp::detail
     MetricSet::MetricSet(Metrics... metrics)
     {
         metrics_.reserve(sizeof...(metrics));
-        (metrics_.push_back(std::make_unique<Metrics>(std::move(metrics))), ...);
+        ( metrics_.push_back(std::make_unique<Metrics>(std::move(metrics))), ... );
     }
 
     template<typename Metric>
@@ -60,8 +60,7 @@ namespace gapp::detail
     {
         auto found = std::find_if(metrics_.begin(), metrics_.end(), [](const auto& metric) { return metric->type_id() == detail::type_id<Metric>; });
 
-        if (found == metrics_.end()) return nullptr;
-        return static_cast<const Metric*>(found->get());
+        return found != metrics_.end() ? static_cast<Metric*>(found->get()) : nullptr;
     }
 
 } // namespace gapp::detail

src/metrics/misc_metrics.cpp

@@ -22,11 +22,4 @@ namespace gapp::metrics
         data_.push_back(sum_ - old_sum);
     }
 
-    size_t FitnessEvaluations::value_at(size_t generation) const noexcept
-    {
-        GAPP_ASSERT(generation < data_.size());
-
-        return data_[generation];
-    }
-
 } // namespace gapp::metrics

src/metrics/misc_metrics.hpp

@@ -12,9 +12,6 @@ namespace gapp::metrics
     /** Record the number of fitness function evaluations performed in each generation. */
     class FitnessEvaluations final : public Monitor<FitnessEvaluations, std::vector<size_t>>
     {
-    public:
-        size_t value_at(size_t generation) const noexcept;
-    private:
         void initialize(const GaInfo& ga) override;
         void update(const GaInfo& ga) override;
 

src/metrics/monitor.hpp

@@ -6,6 +6,8 @@
 #include "monitor_base.hpp"
 #include "../utility/type_id.hpp"
 #include "../utility/type_traits.hpp"
+#include "../utility/concepts.hpp"
+#include "../utility/utility.hpp"
 #include <vector>
 #include <type_traits>
 #include <cstddef>
@@ -17,26 +19,24 @@ namespace gapp::metrics
     * Metrics can be used to track certain attributes of the %GAs
     * in every generation throughout a run.
     * 
-    * New metrics should be derived from this class, and they should implement the following 3 methods:
+    * New metrics should be derived from this class, and they should implement the following methods:
     *   
-    *   - initialize : Used to initialize the monitor at the start of a run.
-    *   - update     : Used to update the monitored attribute once every generation.
-    *   - value_at   : Returns the value of the monitored metric in a specific generation
-                        (must be implemented as a public, non-virtual function).
+    *   - initialize (optional) : Used to initialize the monitor at the start of a run.
+    *   - update                : Used to update the monitored attribute once every generation.
     * 
     * @note The monitor doesn't have access to any encoding specific information about a %GA
     *   by default, so no such information can be tracked.
     * 
     * @tparam Derived The type of the derived class.
     * @tparam MetricData The type of the container used to store the monitored metrics (eg. std::vector).
     */
-    template<typename Derived, typename MetricData>
+    template<typename Derived, detail::IndexableContainer MetricData>
     class Monitor : public MonitorBase
     {
     public:
         /** @returns The value of the tracked metric in the specified @p generation. */
         [[nodiscard]]
-        constexpr decltype(auto) operator[](size_t generation) const { return derived().value_at(generation); }
+        constexpr auto operator[](size_t generation) const noexcept { GAPP_ASSERT(generation < data_.size()); return data_[generation]; }
 
         /** @returns The data collected by the monitor throughout the run. */
         [[nodiscard]]
@@ -47,28 +47,17 @@ namespace gapp::metrics
         constexpr size_t size() const noexcept { return data_.size(); }
 
         /** @returns An iterator to the first element of the metric data. */
-        constexpr auto begin() const { return data_.begin(); }
+        constexpr auto begin() const noexcept { return data_.begin(); }
 
         /** @returns An iterator to one past the last element of the metric data. */
-        constexpr auto end() const   { return data_.end(); }
+        constexpr auto end() const noexcept { return data_.end(); }
+
+        void initialize(const GaInfo&) override { data_.clear(); }
 
     protected:
         MetricData data_;
 
-        constexpr Monitor() noexcept
-        {
-            static_assert(!std::is_abstract_v<Derived>,
-                          "The Derived class should implement all the virtual functions of Monitor.");
-            static_assert(detail::is_derived_from_spec_of_v<Derived, Monitor>,
-                          "The first type parameter of the Monitor class must be the derived class.");
-            static_assert(std::is_invocable_v<decltype(&Derived::value_at), const Derived&, size_t>,
-                          "Classes derived from Monitor must implement a public 'value_at(size_t) const' function.");
-        }
-
         size_t type_id() const noexcept final { return detail::type_id<Derived>; }
-
-    private:
-        constexpr const Derived& derived() const noexcept { return static_cast<const Derived&>(*this); }
     };
 
 } // namespace gapp::metrics

test/unit/metrics.cpp

@@ -31,9 +31,9 @@ TEMPLATE_TEST_CASE("fitness_metrics", "[metrics]", FitnessMin, FitnessMax, Fitne
     REQUIRE(metric.data().size() == num_gen);
 
     REQUIRE(std::all_of(metric.begin(), metric.end(), detail::is_size(num_obj)));
-    REQUIRE(metric.value_at(4).size() == num_obj);
+    REQUIRE(metric[4].size() == num_obj);
 
-    const auto& val = metric.value_at(7);
+    const auto& val = metric[7];
     REQUIRE(std::all_of(val.begin(), val.end(), detail::equal_to(0.0)));
 }
 
@@ -48,7 +48,7 @@ TEST_CASE("nadir_point_metric", "[metrics]")
     REQUIRE(metric.size() == num_gen);
     REQUIRE(std::all_of(metric.begin(), metric.end(), detail::is_size(num_obj)));
 
-    const auto& val = metric.value_at(5);
+    const auto& val = metric[5];
     REQUIRE(std::all_of(val.begin(), val.end(), detail::equal_to(0.0)));
 }