Partial partial function application.

partialpartial.cpp

#include <cstdio>

template <typename R, typename A1, typename... Args>
class _partialpartial
{
    public:
        typedef R R_type;
    
        _partialpartial(R (*func_)(A1, Args...),
                        A1 arg1_) : func(func_), arg1(arg1_) {}
        
        inline R operator () (Args... args) const
        {
            return func(arg1, args...);
        }
    private:
        R (*func)(A1, Args...);
        A1 arg1;
};

template <typename Partial, typename A1>
class _partialpartial2
{
    public:
        typedef typename Partial::R_type R_type;
    
        _partialpartial2(const Partial& partial,
                         A1 arg1_) : func(partial),
                                     arg1(arg1_) {}
        
        template <typename... Args>
        inline R_type operator () (Args... args) const
        {
            return func(arg1, args...);
        }
    private:
        Partial func;
        A1 arg1;
};

template <typename R, typename A1, typename... Args>
inline _partialpartial<R, A1, Args...> partialpartial(R (*func)(A1, Args...), const A1& arg1)
{
    return _partialpartial<R, A1, Args...>(func, arg1);
}

template <typename Partial, typename A1>
inline _partialpartial2<Partial, A1> partialpartial(const Partial& partial_, const A1& arg1)
{
    return _partialpartial2<Partial, A1>(partial_, arg1);
}

int add3(int a, int b, int c)
{
    return a + b + c;
}

int main(int argc, char *argv[])
{
    auto add = partialpartial(add3, 0);
    auto inc = partialpartial(add, 1);
    
    std::printf("5 + 1 = %d\n", inc(5));
    
    auto six = partialpartial(inc, 5);
    
    std::printf("6 = %d\n", six());
}