scored_individual.h

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#if !defined(ULTRA_SCORED_INDIVIDUAL_H)
#define      ULTRA_SCORED_INDIVIDUAL_H
 
#include "kernel/individual.h"
#include "kernel/fitness.h"
#include "kernel/problem.h"
 
#include <utility>
 
namespace ultra
{

/// \tparam I type modelling an individual
/// \tparam F type modelling a fitness value
///
/// `scored_individual` is a lightweight value type used to represent the
/// result of evaluating an individual. It is primarily intended for **ranking,
/// selection, and replacement** operations in evolutionary algorithms.
///
/// The class supports *ordering by fitness* (via `operator<=>`) but
/// deliberately does **not** define equality. Fitness values are typically
/// floating-point and exact equality comparisons would be semantically
/// misleading.
///
/// \note
/// Since equality is not defined, `scored_individual` does not model a totally
/// ordered type and cannot be used with default `std::ranges::less`.
/// Algorithms that require ordering should provide an explicit comparator or
/// projection (e.g. comparing the `fit` member).
///
template<Individual I, Fitness F>
struct scored_individual
{
  // ---- Constructor and support functions ----
  scored_individual() = default;
  scored_individual(I, F);
 
  // ---- Capacity ----
  [[nodiscard]] bool empty() const noexcept;
 
  // ---- Serialization ----
  [[nodiscard]] bool load(std::istream &, const problem &);
  [[nodiscard]] bool save(std::ostream &) const;
 
  // ---- Data members ----
  I ind {};
  F fit {lowest<F>()};
};
 
 
// ---- Non-member functions ----
template<Individual I, Fitness F>
[[nodiscard]] auto operator<=>(const scored_individual<I, F> &,
                               const scored_individual<I, F> &) noexcept;
 
#include "kernel/scored_individual.tcc"
 
}  // namespace ultra
 
#endif  // include guard