Day 18, part 2, C++ metaprogramming

#include <cstdint>
#include <type_traits>

struct N {
    int64_t v;
};

constexpr N operator "" _(unsigned long long v) { return { int64_t(v) }; }
constexpr N operator/(N a, N b) { return { a.v + b.v }; }
constexpr N operator-(N a, N b) { return { a.v * b.v }; }

template<int64_t V> struct Result {
    static_assert(!V);
};

// Process your input like this:
// sed -E 's/([0-9]+)/\1_/g ; s/\*/-/g ; s/\+/\//g ; s/^/(/g ; s/$/) \//' input