小编Nic*_*las的帖子

我有这些课程：

#include <type_traits>

template <typename T>
class A {
public:
    static_assert(std::is_default_constructible_v<T>);

};

struct B {
   struct C {
      int i = 0;
   };

    A<C> a_m;
};

int main() {
    A<B::C> a;
}

编译时，a_m不是默认可构造的，而是a可构造的。

更改C为：

struct C {
      int i;
   };

一切安好。

使用 Clang 9.0.0 测试。

我很难理解这段代码发生了什么：

#include <iostream>
#include <variant>

template <class... Ts>
struct overloaded : Ts... {
    using Ts::operator()...;
};
template <class... Ts>
overloaded(Ts...) -> overloaded<Ts...>;

struct FirstPSet {
    std::uint16_t uid;
};

struct SecondPSet {
    std::uint16_t uid;
};

using PSet = std::variant<std::monostate, FirstPSet, SecondPSet>;

auto getUID(const PSet& pSet) {
    auto visitor = overloaded{[](const std::monostate&) -> std::uint16_t { return 0; },
                              [](const auto& pSet) -> std::uint16_t { return pSet.uid; }};
    return std::visit(visitor, pSet);
}

int main() {
    FirstPSet pSet{42};

    std::cout << getUID(pSet) << '\n';
} …

我们有这样的代码：

template <typename T>
struct A {
    static constexpr A a = A{};
};


template <typename T>
struct B {
    T a;
};

B<A<int>> b;

GCC 13 似乎对 L.3 感到满意，但对 clang 16 不满意。

<source>:3:21: error: constexpr variable cannot have non-literal type 'const A<int>'
        static constexpr A a = A{};
                           ^
<source>:9:4: note: in instantiation of template class 'A<int>' requested here
        T a;
          ^
<source>:12:11: note: in instantiation of template class 'B<A<int>>' requested here
B<A<int>> b;
          ^
<source>:3:21: note: incomplete type …

当我遇到问题时,我试图在Vim 7.3中自定义我的状态行.

我正在尝试将SVN信息放在状态行中,所以我做了类似这样的事情:

function! DrawStatusLine()
    let svn = system("svn info")
    let l:status = " "
    let l:status = l:status . svn
    let l:status = l:status . "%t"       "tail of the filename
    let l:status = l:status . "%*"
    let l:status = l:status . "[%{strlen(&fenc)?&fenc:'none'}," "file encoding
    let l:status = l:status . "%{&ff}]" "file format
    let l:status = l:status . "%h"      "help file flag
    let l:status = l:status . "%m"      "modified flag
    let l:status = l:status . "%r"      "read only flag
    let …