c – std :: swap用于不可复制但可移动的结构

概述根据 C++ reference std :: swap相当于 T c(std::move(a)); a=std::move(b); b=std::move(c); 这应该允许交换两个不可复制但可移动的物体.所以我不明白为什么 #include<utility>struct Foo { Foo() = delete; Foo(int) {}; Foo(Foo &) = delete 根据 C++ reference std :: swap相当于

T c(std::move(a)); a=std::move(b); b=std::move(c);

这应该允许交换两个不可复制但可移动的物体.所以我不明白为什么

#include<utility>struct Foo {  Foo() = delete;  Foo(int) {};  Foo(Foo &) = delete;  Foo(Foo &&) {};  ~Foo() {};};int main() {  Foo a(1),b(2);  std::swap(a,b);}

被编译器拒绝

In file included from /usr/include/c++/4.8/bits/stl_pair.h:59:0,from /usr/include/c++/4.8/utility:70,from swap.cpp:1:/usr/include/c++/4.8/bits/move.h: In instantiation of ‘voID std::swap(_Tp&,_Tp&) [with _Tp = Foo]’:swap.cpp:13:16:   required from here/usr/include/c++/4.8/bits/move.h:176:11: error: use of deleted function ‘Foo& Foo::operator=(const Foo&)’       __a = _GliBCXX_MOVE(__b);           ^swap.cpp:3:8: note: ‘Foo& Foo::operator=(const Foo&)’ is implicitly declared as deleted because ‘Foo’ declares a move constructor or move assignment operator struct Foo {        ^In file included from /usr/include/c++/4.8/bits/stl_pair.h:59:0,from swap.cpp:1:/usr/include/c++/4.8/bits/move.h:177:11: error: use of deleted function ‘Foo& Foo::operator=(const Foo&)’       __b = _GliBCXX_MOVE(__tmp);

注意：这是GCC 4.8和4.9,但clang也抱怨.

解决方法 你声明了一个移动构造函数.但是,您需要std :: swap的移动赋值运算符.您应该添加以下两个运算符：

auto operator=(const Foo& rhs) & -> Foo& = delete;auto operator=(Foo&& rhs) & noexcept -> Foo&{    // ...    return *this;}

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