std::meta (Meta-Programming, Proposed)

#include <meta> auto meta = std::meta::info<decltype(obj)>(); // Proposed

// CodeNebula - C++26 Example: Compile-Time Meta-Programming (std::meta)
// Compile: g++ -std=c++26 -Wall -Wextra -o example meta_programming.cpp
// Note: Requires C++26 compiler support (GCC 15+ / Clang 19+ expected)

// C++26 std::meta provides compile-time meta-programming facilities built
// on top of static reflection. You can generate code, create new types,
// and transform declarations entirely at compile time.

#include <iostream>
#include <string>
#include <tuple>

// --- C++26 std::meta Syntax (not yet compilable) ---
//
// #include <meta>
//
// // Generate a tuple type from struct members
// template<typename T>
// using to_tuple_t = [: std::meta::substitute(
//     ^^std::tuple,
//     std::meta::nonstatic_data_members_of(^^T)
//         | std::views::transform(std::meta::type_of)
//         | std::ranges::to<std::vector>()
// ) :];
//
// struct RGB { int r; int g; int b; };
// // to_tuple_t<RGB> is std::tuple<int, int, int>
//
// // Create a function that converts struct to tuple
// template<typename T>
// auto struct_to_tuple(const T& obj) {
//     return [: std::meta::nonstatic_data_members_of(^^T) :]
//         >> [&]<auto... mems> {
//             return std::make_tuple(obj.[:mems:]...);
//         };
// }

// --- Simulation using C++20 features ---

struct RGB { int r; int g; int b; };

// Manually written: C++26 reflection would auto-generate this
using RGB_tuple_t = std::tuple<int, int, int>;

auto struct_to_tuple(const RGB& obj) {
    return std::make_tuple(obj.r, obj.g, obj.b);
}

// Simulate compile-time member count (would be automatic with std::meta)
template<typename T>
constexpr size_t member_count() {
    if constexpr (std::is_same_v<T, RGB>) return 3;
    return 0;
}

int main() {
    std::cout << "=== C++26 std::meta Meta-Programming (Simulated) ===" << std::endl;

    RGB color{255, 128, 0};

    auto t = struct_to_tuple(color);
    std::cout << "RGB{255,128,0} as tuple: ("
              << std::get<0>(t) << ", "
              << std::get<1>(t) << ", "
              << std::get<2>(t) << ")" << std::endl;

    std::cout << "Member count of RGB: " << member_count<RGB>() << std::endl;

    // Show the type equivalence
    static_assert(std::is_same_v<RGB_tuple_t, std::tuple<int, int, int>>);
    std::cout << "to_tuple_t<RGB> == tuple<int,int,int>: true" << std::endl;

    std::cout << "std::meta automates struct-to-tuple, serialization, "
              << "and code generation." << std::endl;
    return 0;
}

// Expected output:
// === C++26 std::meta Meta-Programming (Simulated) ===
// RGB{255,128,0} as tuple: (255, 128, 0)
// Member count of RGB: 3
// to_tuple_t<RGB> == tuple<int,int,int>: true
// std::meta automates struct-to-tuple, serialization, and code generation.