C++ 中文周刊 第76期

std::expected<std::vector<int>, Status> ReadData()
{
   if (!HasAcccess())
      return std::unexpected<Status> { Status::AccessDenied };
   if (OpenConnection() != 0)
      return std::unexpected<Status> {Status::DataSourceError};
   if (Fetch() != 0)
      return std::unexpected<Status> {Status::DataError};
   std::vector<int> data;
   data.push_back(42);
   return data;
}

void report_error();
[[gnu::cold]] void report_error_cold();
void logic();

/*
cold(bool):
        test    edi, edi
        jne     .LBB0_1
        jmp     logic()
.LBB0_1:
        jmp     report_error_cold()
*/
auto cold(bool error) {
    if (error) {
        report_error_cold();
        return;
    }

    logic();
}

/*
normal(bool):
        test    edi, edi
        je      .LBB1_2
        jmp     report_error()
.LBB1_2:
        jmp     logic()
*/
auto normal(bool error) {
    if (error) {
        report_error();
        return;
    }

    logic();
}

/*
unlikely(bool):
        test    edi, edi
        jne     .LBB2_1
        jmp     logic()
.LBB2_1:
        jmp     report_error()
*/
auto unlikely(bool error) {
    if (error) [[unlikely]] {
        report_error();
        return;
    }

    logic();
}

// #embed 支持
//#embed </path/to/file.txt>

//constexpr 部分支持
// not allowed in c23 :(
//constexpr int get_value() {
//  return 42;
//}
// allowed in c23!
constexpr int universe_and_everything = 42;

// [[attributes]]支持
[[nodiscard]] int get_value();
// deprecated, fallthrough, maybe_unused, nodiscard, noreturn

// 未命名参数
int do_work(int x, int)
{
  return x * 23;
}

// 类型枚举
enum MyEnum : char {
  x,
  y
};

// #6 __has_include
#if __has_include("somefile")
#include("somefile");
#endif

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