使用 std::addressof 时出现 GCC 7 编译错误

Question

我观察到一些我自己无法完全解释的奇怪行为。 代码如下所示：

#include <memory>
#include <vector>
#include <algorithm>

int main(){
    std::vector<double> t1(10, 5.0);
    std::vector<double*> t2(10);
    std::transform(t1.begin(), t1.end(), t2.begin(), std::addressof<double>);
    //std::transform(t1.begin(), t1.end(), t2.begin(), [](double& a){return &a;});
}

这里有一个与https://godbolt.org/g/YcNdbf 一起玩的版本 问题是这段代码使用 gcc4.9-6.3 编译得很好，但在 gcc 7.1 下编译失败。 Clang 也不喜欢。

（编辑）来自 gcc 7.1 的错误消息：

<source>: In function 'int main()':
8 : <source>:8:76: error: no matching function for call to 'transform(std::vector<double>::iterator, std::vector<double>::iterator, std::vector<double*>::iterator, <unresolved overloaded function type>)'
     std::transform(t1.begin(), t1.end(), t2.begin(), std::addressof<double>);
                                                                            ^
In file included from /opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/algorithm:62:0,
                 from <source>:3:
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/stl_algo.h:4281:5: note: candidate: template<class _IIter, class _OIter, class _UnaryOperation> _OIter std::transform(_IIter, _IIter, _OIter, _UnaryOperation)
     transform(_InputIterator __first, _InputIterator __last,
     ^~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/stl_algo.h:4281:5: note:   template argument deduction/substitution failed:
8 : <source>:8:76: note:   could not resolve address from overloaded function 'addressof<double>'
     std::transform(t1.begin(), t1.end(), t2.begin(), std::addressof<double>);
                                                                            ^
In file included from /opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/algorithm:62:0,
                 from <source>:3:
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/stl_algo.h:4318:5: note: candidate: template<class _IIter1, class _IIter2, class _OIter, class _BinaryOperation> _OIter std::transform(_IIter1, _IIter1, _IIter2, _OIter, _BinaryOperation)
     transform(_InputIterator1 __first1, _InputIterator1 __last1,
     ^~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/stl_algo.h:4318:5: note:   template argument deduction/substitution failed:
8 : <source>:8:76: note:   could not resolve address from overloaded function 'addressof<double>'
     std::transform(t1.begin(), t1.end(), t2.begin(), std::addressof<double>);
                                                                            ^
Compiler exited with result code 1

但是，我不太明白为什么它不起作用。

提前感谢任何试图提供帮助的人:)

Answer 1

为避免意外获取临时地址，图书馆为addressof 获得了第二个（已删除）签名：

template <class T> constexpr T* addressof(T& r) noexcept;
template <class T> const T* addressof(const T&& elem) = delete;

见http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2598

所以现在编译器不知道你的代码是否应该匹配被删除的函数......