C++ 中文周刊第124期

王很水

发布于 2024-07-30 14:17:15

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发布于 2024-07-30 14:17:15

文章被收录于专栏：C++ 动态新闻推送

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请提交 issue[1]

感谢 振羽 不语 赞助

资讯

标准委员会动态/ide/编译器信息放在这里

七月邮件列表

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/#mailing2023-07

文章

• 理论上所有编程语言都可以编译成LLVM IR，请问为什么他们之间还会存在性能差异呢[2]

有点意思

• Did you know that C++26 added bind front and back to NTTP callables? [3]

struct foo {
  auto bar(int v) { return v; }
};

static_assert(42 == std::bind_front<&foo::bar>(foo{}, 42));

不懂啥意思

• Notes on float and multi-byte delta compression[4]
• Float to int casts for data compression [5]

讲浮点数压缩的，没看懂。这里标记个TODO后面研究一下

• Decoding base16 sequences quickly[6]

SIMD时间，这回不贴代码了。https://github.com/lemire/Code-used-on-Daniel-Lemire-s-blog/tree/master/2023/07/27

• Nubbing lists in C++[7]

作者想把

constexpr std::tuple<int, double, int, double, float> { 1, 2.0, 1, 3.0, 2.0 }

变成 constexpr std::tuple<int, double, double, float> { 1, 2.0, 3.0, 2.0 }简单方案就是boost::mp_list,或者看这个 https://stackoverflow.com/questions/55941964/how-to-filter-duplicate-types-from-tuple-c

但作者想要的是如果值相等才把类型吃掉，有点点难

直接贴代码吧，我看不懂，作者推导了半天

#include <functional>
#include <tuple>

template<typename T1, typename T2>
consteval bool JMEq(const T1& v1, const T2& v2) {
    if constexpr (!std::is_same_v<T1, T2>)
        return false;
    else
        return v1 == v2;
}

template<const auto& F>
constexpr auto Nub() {
    constexpr auto tup = F();
    constexpr auto indices = std::make_index_sequence<std::tuple_size_v<decltype(tup)>> {};

    return [&]<std::size_t... Ix>(std::index_sequence<Ix...>)
    {
        return std::tuple_cat ([&]
            {
                constexpr auto index = Ix;
                constexpr auto element = std::get<index>(tup);

                if constexpr (((JMEq(element, std::get<Ix>(tup)) && Ix < index) || ...))
                    return std::tuple {};
                else
                    return std::tuple { element };
            } ()...);
    } (indices);
}

constexpr auto structuralize(auto tuple){
    return std::apply([]<typename... Args>(Args... args) { return ST<Args...>(args...); }, tuple);
}

constexpr std::tuple<int, double, int, double, float> input { 1, 2.0, 1, 3.0, 2.0 };
constexpr std::tuple<double, int, double, float> expected { 2.0, 1, 3.0, 2.0 };
constexpr auto actual = Nub<structuralize(input)>();
static_assert(expected == actual);

• C++23: static operator() and static operator[][8]

简单说就是lambda是对象，有时候不捕获的lambda也是对象，和函数指针差不多，太浪费了，于是引入了static lambda,static operator

auto isEven = [](int i) static {return i % 2 == 0;};

如果捕获会报错

//

 ERROR: 'static' lambda specifier with lambda capture
auto isDivisableBy = [operand](int i) static {return i % operand == 0;};

其实static operator[]原因也差不多。代码就不列举了

Perfect forwarding forwards objects, not braced things that are trying to become objects[9]

forward对于 initializer_list对象行不通，initializer_list真该死啊

template<typename T, typename... Args>
std::unique_ptr<T> make_unique(Args&&... args){
    return std::unique_ptr<T>(
        new T(std::forward<Args>(args)...));
}

这样就不行

struct Point {
    int x, y;
};

struct Segment {
    Segment(Point p1, Point p2);
};

void test() {
    // This works
    Segment s({ 1, 1 }, { 2, 2 });

    // This doesn't
    auto p = std::make_unique<Segment>(
        { 1, 1 }, { 2, 2 });
}

封装一层吧

struct Segment {
    Segment(Point p1, Point p2);
    template<typename Arg1 = Point,
             typename Arg2 = Point>
    static std::unique_ptr<Segment> make_unique(
        Arg1&& p1, Arg2&& p2) {
        return std::make_unique<Segment>(
            std::forward<Arg1>(p1),
            std::forward<Arg2>(p2));
    }
};

这样就行了

• Why does IAsyncAction or IAsyncOperation.GetResults() produce a E_ILLEGAL_METHOD_CALL [10]
• On the various ways of creating Windows Runtime delegates in C++/WinRT and C++/CX[11]

讲winrt的。不说了

视频

本周视频很多 cppnow 2023来了。基本上讲的是今年cppcon的前瞻内容

• A Deep Dive Into Dispatching Techniques in C++ - Jonathan Müller - CppNow 2023[12]

这个是之前他写的博客，直接做成视频讲了一遍，就是讲用tag dispatch替换switch加速的

ppt在这里 https://github.com/boostcon/cppnow_presentations_2023/blob/main/cppnow_slides/A_Deep_dive_into_dispatching_techniques.pdf

周末有空我就传一下

• Introduction to C++ Coroutines Through a Thread Scheduling Demonstration - Dian-Lun Lin CppNow 2023[13]

这个华人哥们讲的也有点意思

• Non-Uniform Memory Architecture (NUMA): A Nearly Unfathomable Morass of Arcana - Fedor Pikus CppNow[14]

介绍numa的，有点意思

• Obfuscate Logs Without an External Script by Executing Uninvoked C++ Code - Andrei Zissu CppNow 23[15]

敏感字符串过滤？hash绕过

• Data-Oriented Design and Modern C++ - Floris Bob van Elzelingen - CppNow 2023[16]

感觉之前说过，还是布局之类的。没有细看

• C++ Coroutine Intuition - Roi Barkan - CppNow 2023[17]

这个教程也不错，手把手带你了解协程以及一个task模型

• C++ Electronic Trading for Cpp Programmers - Mathias Gaunard - ACCU 2023[18]

讲高频交易的，很干货。值得一看

• Introduction to Epoch-Based Memory Reclamation - Jeffrey Mendelsohn - ACCU 2023[19]

讲基于epoch的内存回收的。epoch推进技术其实已经不是新东西了。到处都可见，或多或少要了解一下。了解背景之后值得看看

开源项目需要人手

• asteria[20] 一个脚本语言，可嵌入，长期找人，希望胖友们帮帮忙，也可以加群384042845和作者对线
• Unilang[21] deepin的一个通用编程语言，点子有点意思，也缺人，感兴趣的可以github讨论区或者deepin论坛看一看。这里也挂着长期推荐了
• gcc-mcf[22] 懂的都懂

新项目介绍/版本更新

• https://github.com/bloomberg/blazingmq 有点意思
• mold 2.0发布 https://github.com/rui314/mold/releases/tag/v2.0.0 之前商业化license发展不是很顺利，又改成MIT了，寻求赞助开源真难搞啊

工作招聘

• 求不需要算法题笔试的可以远程的工作，我的邮箱wanghenshui@qq.com[23]

本文永久链接[24]

如果有疑问评论最好在上面链接到评论区里评论，这样方便搜索，微信公众号有点封闭/知乎吞评论

引用链接

[1] 提交 issue: https://github.com/wanghenshui/cppweeklynews/issues [2] 理论上所有编程语言都可以编译成LLVM IR，请问为什么他们之间还会存在性能差异呢: https://www.zhihu.com/question/545005023/answer/3132407932 [3] Did you know that C++26 added bind front and back to NTTP callables? : https://github.com/tip-of-the-week/cpp/blob/master/tips/340.md [4] Notes on float and multi-byte delta compression: https://cbloomrants.blogspot.com/2023/07/notes-on-float-and-multi-byte-delta.html [5] Float to int casts for data compression : http://cbloomrants.blogspot.com/2023/07/float-to-int-casts-for-data-compression.html [6] Decoding base16 sequences quickly: https://lemire.me/blog/2023/07/27/decoding-base16-sequences-quickly/ [7] Nubbing lists in C++: https://0xd34df00d.me//posts/2023/07/nubbing-lists.html [8] C++23: static operator() and static operator[]: https://www.sandordargo.com/blog/2023/07/26/cpp23-static-call-and-subscript-operator [9] Perfect forwarding forwards objects, not braced things that are trying to become objects: https://devblogs.microsoft.com/oldnewthing/20230727-00/?p=108494 [10] Why does IAsyncAction or IAsyncOperation.GetResults() produce a E_ILLEGAL_METHOD_CALL : https://devblogs.microsoft.com/oldnewthing/20230724-00/?p=108477 [11] On the various ways of creating Windows Runtime delegates in C++/WinRT and C++/CX: https://devblogs.microsoft.com/oldnewthing/20230726-00/?p=108487 [12] A Deep Dive Into Dispatching Techniques in C++ - Jonathan Müller - CppNow 2023: https://www.youtube.com/watch?v=vUwsfmVkKtY&ab_channel=CppNow [13] Introduction to C++ Coroutines Through a Thread Scheduling Demonstration - Dian-Lun Lin CppNow 2023: https://www.youtube.com/watch?v=kIPzED3VD3w&ab_channel=CppNow [14] Non-Uniform Memory Architecture (NUMA): A Nearly Unfathomable Morass of Arcana - Fedor Pikus CppNow: https://www.youtube.com/watch?v=f0ZKBusa4CI&ab_channel=CppNow [15] Obfuscate Logs Without an External Script by Executing Uninvoked C++ Code - Andrei Zissu CppNow 23: https://www.youtube.com/watch?v=R7RcvNsg0yo&ab_channel=CppNow [16] Data-Oriented Design and Modern C++ - Floris Bob van Elzelingen - CppNow 2023: https://www.youtube.com/watch?v=GoIOnQEmXbs&ab_channel=CppNow [17] C++ Coroutine Intuition - Roi Barkan - CppNow 2023: https://www.youtube.com/watch?v=NNqVt73OsfI&ab_channel=CppNow [18] C++ Electronic Trading for Cpp Programmers - Mathias Gaunard - ACCU 2023: https://www.youtube.com/watch?v=ltT2fDqBCEo&ab_channel=ACCUConference [19] Introduction to Epoch-Based Memory Reclamation - Jeffrey Mendelsohn - ACCU 2023: https://www.youtube.com/watch?v=KHVEiSHaEDQ&ab_channel=ACCUConference [20] asteria: https://github.com/lhmouse/asteria [21] Unilang: https://github.com/linuxdeepin/unilang [22] gcc-mcf: https://gcc-mcf.lhmouse.com/ [23] wanghenshui@qq.com: mailto:wanghenshui@qq.com [24] 本文永久链接: https://wanghenshui.github.io/cppweeklynews/posts/124.html