MCMCable.h

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#pragma once

#include <optional>
#include "Bayesable.h"

template<typename this_t, typename... Args>
class MCMCable : public Bayesable<Args...> {
public:
    MCMCable() { }

    // these are declared nodiscard (and must be in subclasses too) to help remind that they do NOT modify the hypothesis,
    // instead they return a new one
    [[nodiscard]] virtual std::optional<std::pair<this_t,double>> propose() const = 0; // return a proposal and its forward-backward probs
    [[nodiscard]] virtual this_t                   restart() const = 0; // restart a new chain -- typically by sampling from the prior, but actually it only resamples can_resample 
    virtual bool operator==(const this_t& h)                 const = 0; // speeds up a check in MCMC
    
    [[nodiscard]] static this_t sample() {
        assert(false && "*** This should not be called -- must be overwritten in derived class");
    }
    
    
    virtual bool operator!=(const this_t& h) const {
        return not this->operator==(h);
    }
};