if(a==1) return 1 DO MAKE SENSE in C++

consteval_forwarding.cpp

// fun thing that `if a==1 f(1);if a==2 f(2)` do make sense in c++

#include <cstdint>
#include <format>
#include <iostream>
#include <string_view>
#include <tuple>

using namespace std;

enum E : int {
    FOO = 0,
    BAR,
    BAZ,
};

#define MAP(K, ...)         \
    case K: {               \
        return __VA_ARGS__; \
    }
#define MAP_BEGIN_WITH(V) switch (V) {
#define MAP_END()                           \
    default:                                \
        return {0, {"", "name=Anonymous"}}; \
        }

consteval auto static_map(E e) -> tuple<id_t, tuple<string_view, string_view>> {
    MAP_BEGIN_WITH(e)
    MAP(FOO, {1234, {"FOO", "name=Foo"}})
    MAP(BAR, {2345, {"BAR", "name=Bar"}})
    MAP(BAZ, {34567, {"BAZ", "name=Baz"}})
    MAP_END()
}

// this function may not be as easy as you've thought
void print_static_map(E e) {
    static_map(FOO);  // work
    // static_map(e); // can't work

    // this lambda is conteval, thus the static_map() work
    auto flatten = [](E _e) consteval {
        auto [id, extra] = static_map(_e);
        auto [name, info] = std::move(extra);
        return make_tuple(static_cast<int>(_e), id, name, info);
    };

    flatten(FOO);  // work because called with constexpr
    // flatten(e); // can't work

    // now it's time to play with the "dumb forwarding"
    auto to_runtime = [](auto f, E _e) {
        switch (_e) {
            case FOO:
                return f(FOO);
            case BAR:
                return f(BAR);
            case BAZ:
                return f(BAZ);
            default:
                return f(E(-1));
        }
    };

    cout << std::apply(
        [](auto &&...args) {
            return std::format("in case {}, id {} (name:{}) has info: {}\n",
                               args...);
        },
        // flatten(FOO));  // work, but only with literal
        to_runtime(flatten, e));  // work at runtime
}

int main() {
    print_static_map(FOO);
    print_static_map(BAR);
    print_static_map(BAZ);
    print_static_map(E(-1));
}