C ++ 20に一歩近づいた。 トロントでの会議の結果

• C ++ 20の拡張機能の概念！
• 範囲、ネットワーク、コルーチン/コルーチン：TSの形で実験としてリリースされました。
• モジュール：TSドラフトの準備ができました。

コンセプト

#include <iostream>

template <class Container, class Data>
void compute_vector_fast(Container& v, const Data& data) {
    std::cout << "fast\n";
    // ...
}

template <class Container, class Data>
void compute_vector_slow(Container& v, const Data& data) {
    std::cout << "slow\n";
    // ...
}

template <class Container, class Data>
void compute_vector_optimal(Container& v, const Data& data) {
    // ??? call `compute_vector_slow(v, data)` or `compute_vector_fast(v, data)` ???
}

#include <iostream>

template <class T, class Data>
concept bool VectorOperations = requires(T& v, const Data& data) {
    { v += data } -> T&;
    { v -= data } -> T&;
    { v *= data } -> T&;
    { v /= data } -> T&;
};

template <class Container, class Data>
    requires VectorOperations<Container, Data>
void compute_vector_optimal(Container& v, const Data& data) {
    std::cout << "fast\n";
}

template <class Container, class Data>
void compute_vector_optimal(Container& v, const Data& data) {
    std::cout << "slow\n";
}

• ,
• ( , !).

Ranges TS

#include <vector>
#include <experimantal/ranges/algorithm>
namespace ranges = std::experimental::ranges;

int main () {
    //  get_some_values_and_delimiter()  ,
    //      42
    std::vector<int> v2 = get_some_values_and_delimiter();

    //    42    ,   :
    auto it = ranges::find(v.begin(), ranges::unreachable{}, 42);
    ranges::sort(++it, v.end());
}

Networking TS

• Networking TS move-only callback. ASIO BOOST_ASIO_DISABLE_HANDLER_TYPE_REQUIREMENTS. unique_ptr, callback.
• constexpr (, ip::address).
• : -callback allocator_type allocator_type get_allocator(); associated_allocator , get_allocator().

Coroutines TS

#include <ctime>
#include <iostream>
#include <string>
#include <experimental/net>

using net = std::experimental::net;
using net::ip::tcp;

std::string make_daytime_string() {
    using namespace std; // For time_t, time and ctime;
    time_t now = time(0);
    return ctime(&now);
}

void start_accept(net::io_context& io_service) {
    tcp::acceptor acceptor{io_service, tcp::endpoint(tcp::v4(), 13)};

    while (1) {
        tcp::socket socket(acceptor.get_io_service());
        auto error = co_await acceptor.async_accept(socket, net::co_future);
        if (error) break;

        std::string message = make_daytime_string();
        auto& [error, bytes] = co_await async_write(
            socket, net::buffer(message), net::co_future
        );
        if (error) break;
    }
}

int main() {
    net::io_context io_service;
    io_service.post([&io_service](){
        try {
            start_accept(io_service);
        } catch (const std::exception& e) {
            std::cerr << e.what() << std::endl;
        }
    });

    io_service.run();
}

, C++20

struct S {
    unsigned x1:8 = 42;
    unsigned x2:8 { 42 };
};

if constexpr (std::endian::native == std::endian::big) {
    // big endian
} else if constexpr (std::endian::native == std::endian::little) {
    // little endian
} else {
    // mixed endian
}

struct foo { int a; int b; int c; };
foo b{.a = 1, .b = 2};

auto bar = []<class... Args>(Args&&... args) {
    return foo(std::forward<Args>(args)...);
};

21

• P0652R0 — . , , . .
• P0539R1 — integers, ( ) . ( , ), .
• P0639R0 — `constexpr_allocator` `constexpr_string + constexpr_vector`. , . — .
• P0415R0 — constexpr std::complex. LWG ( constexpr ). C++20.
  
  
  constexpr?

  ++ . constexpr- , constexpr — , .
  
  , constexpr-: [1], [2].
  

• P0457R0 — starts_with ends_with . . , , . proposal.
• P0458R0 — contains(key) member [unordered_]map/set/multimap/multiset. , LWG C++20.

fmt::format("The answer is {}", 42);