functional.h

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#ifndef META_UTIL_FUNCTIONAL_H_
#define META_UTIL_FUNCTIONAL_H_

#include <algorithm>
#include <functional>
#include <map>

namespace meta
{
namespace functional
{

template <class Result, class... Args>
std::function<Result(Args...)> memoize(std::function<Result(Args...)> fun)
{
    return [fun](Args... args)
    {
        static std::map<std::tuple<Args...>, Result> map_;
        auto it = map_.find(std::make_tuple(args...));
        if (it != map_.end())
            return it->second;
        return map_[std::make_tuple(args...)] = fun(args...);
    };
}

template <class Iter, class Function>
Iter argmax(Iter begin, Iter end, Function&& fn)
{
    using T = decltype(*begin);
    return std::max_element(begin, end, [&](const T& a, const T& b)
    {
        return fn(a) < fn(b);
    });
}

}
}
#endif