C++ 中文周刊第51期

从reddit/hackernews/lobsters/meetingcpp摘抄一些c++动态

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资讯

标准委员会动态/ide/编译器信息放在这里

标准委员会二月份邮件列表

异常，太坑了

文章

Linux’s getrandom() Sees A 8450% Improvement With Latest Code

替换了算法，使用black而不是sha1

Chrome V8 源码解读系列

这个人写了很多文章。对浏览器感兴趣的/业界人士可以关注一波。我不太懂就不多说了

My favorite C++20 feature

这玩意, 确实挺方便

auto request = http_request{
  .method = http_method::get,
  .uri = "localhost:7634",
  .headers = { { .name = "Authorization", .value = "Bearer TOKEN" } },
};

解析ponder这个库。对于想学习反射的值得一看

A Good Way to Handle Errors Is To Prevent Them from Happening in the First Place

尽可能把错误处理掉或者用optional /expect / outcame包装处理掉

Returning values and errors

string* UserIP(); //1
string UserIP(string* errmsg); //2
bool GetUserIP(string* ip); //3
bool GetUserIP(string* ip, string* errmsg); //4
Result<string> UserIP(); //5
ResultString UserIP(); //6
string UserIP(); //7

大家觉得哪个接口好？

1肯定不行，2 3 4都需要传进个string处理，比较脏， 5是不是太复杂了，6是简单版本，但是会不会又有ResultDouble之类的东西？7简单，只有ip，errmsg不放进去，也许这个才是最优解？

开放题，没有答案

Implementing the FLIP algorithm

图形学的东西，不太懂，这里标记TODO

Ways to Refactor Toggle/Boolean Parameters in C++

DoImportantStuff(true, false, true, false);

我们都知道这种参数会有莫名其妙的问题，丢失值的信息，一个两个倒还好，多了难免眼花，怎么重构，封装成enum

enum class UseCacheFlag    { False, True };
enum class DeferredFlag    { False, True };
enum class OptimizeFlag    { False, True };
enum class FinalRenderFlag { False, True };

// and call like:
RenderGlyphs(glyphs,
             UseCacheFlag::True, 
             DeferredFlag::False, 
             OptimizeFlag::True, 
             FinalRenderFlag::False);

使用bit flag

#include <type_traits>

struct Glyphs { };

enum class RenderGlyphsFlags
{
    useCache = 1,
    deferred = 2, 
    optimize = 4,
    finalRender = 8,
};

// simplification...
RenderGlyphsFlags operator | (RenderGlyphsFlags a, RenderGlyphsFlags b) {
    using T = std::underlying_type_t <RenderGlyphsFlags>;
    return static_cast<RenderGlyphsFlags>(static_cast<T>(a) | static_cast<T>(b));
    // todo: missing check if the new value is in range...
}

constexpr bool IsSet(RenderGlyphsFlags val, RenderGlyphsFlags check) {
    using T = std::underlying_type_t <RenderGlyphsFlags>;
    return static_cast<T>(val) & static_cast<T>(check);
    // todo: missing additional checks...
}

void RenderGlyphs(Glyphs &glyphs, RenderGlyphsFlags flags)
{
    if (IsSet(flags, RenderGlyphsFlags::useCache)) { }
    else { }

    if (IsSet(flags, RenderGlyphsFlags::deferred)) { }
    else { }

    // ...
}

int main() {
    Glyphs glyphs;
    RenderGlyphs(glyphs, RenderGlyphsFlags::useCache | RenderGlyphsFlags::optimize);                                      
}

结构体

struct RenderGlyphsParam
{
    bool useCache;
    bool deferred;
    bool optimize;
    bool finalRender;
};
void RenderGlyphs(Glyphs &glyphs, const RenderGlyphsParam &renderParam);

// the call:
RenderGlyphs(glyphs,
             {/*useCache*/true, 
             /*deferred*/false, 
             /*optimize*/true, 
             /*finalRender*/false});

c++20我们有了字段构造，字段信息终于有了

struct RenderGlyphsParam
{
    bool useCache;
    bool deferred;
    bool optimize;
    bool finalRender;
};
void RenderGlyphs(Glyphs &glyphs, const RenderGlyphsParam &renderParam);

// the call:
RenderGlyphs(glyphs,
             {.useCache = true, 
              .deferred = false, 
              .optimize = true, 
              .finalRender = false}); 