又谈右值引用与移动构造函数

感觉又来谈谈右值引用了，这次带上了移动构造函数一起谈。初学移动构造函数时，我看到的大致能总结成这么一句话：资源的转移而非拷贝。由于我初学C++（之前写算法题不能算学了C++），很多隐藏的东西我很难搞懂，很多描述令我抓耳挠腮：有的描述说，右值引用可以延长对象的生命周期。怎么个延长法？本来在栈上的东西出了作用域就无了，延长的是谁的生命周期？对于移动构造函数来说，延长的是整个临时对象的生命周期吗？

答案在C++ Primer里说的其实已经挺清楚了：

与拷贝构造函数不同，移动构造函数不分配任何新内存；它接管给定的StrVec中的内存。在接管内存之后，它将给定对象中的指针都置为nullptr。这样就完成了从给定对象的移动操作，此对象将继续存在。最终，移后源对象会被销毁，意味着将在其上运行析构函数。StrVec的析构函数在first_free上调用deallocate。如果我们忘记了改变s.first_free，则销毁移后源对象就会释放掉我们刚刚移动的内存。

此处要注意两点：一是右值引用让编译器知道，这个引用（就是一个存地址的指针）绑定的是一个临时对象，该对象在之后不会被用到，那么编译器就可以安全地转移资源。

什么是资源？一个类A有如下成员变量：

class A
{
private:
    int i;
    std::string s;
}

由于我实在头脑不清晰。我在最开始理解移动构造的时候，认为这种简单类型i也要进行移动。如果这个对象创建到了栈上，比如这样：

int main()
{
	A a1(1,"a1");
...
}

那么i这个变量也应该在栈上。那既然如此，我愚蠢地认为，出现了一个右值引用，引用到了栈上的这个i的变量。那函数结束后，作用域结束，该函数的栈都空了，哪去找这个i的变量引用？

A(A&& other) noexcept : a(other.a), s(std::move(other.s)) {
        std::cout << "Move Construct: " << s << ", a=" << a << "\n";
        other.a = 0;
    }

但是对于string来说比较好理解。string这个字符串实际是建立在堆上的，这里实际上拿的是一个指针。那么右值引用就告诉编译器，这是块后面不会再用到的资源，可以进行转移。于是把这个指针指向的地址（这个地址在堆）复制到新的对象里就好了。不需要在堆里再做资源的拷贝。但一定要注意。在退出移动构造函数之前，如果是自己定义的持有资源的对象，一定要将其清零。不然原对象会销毁我们已经移交了控制权的那块资源。此处string没有做是因为：std::move(other.s)来初始化新对象的s，这会调用std::string的移动构造函数），所以other.s已经被std::string的移动构造函数置为空字符串

那么这种简单变量怎么办呢？

这时候愚蠢的我发现，移动构造函数可以我们自己写，一般直接赋值即可，也就是简单的拷贝操作：

// 移动赋值
    A& operator=(A&& other) noexcept {
        if (this != &other) {
            a = other.a;
            s = std::move(other.s);
            other.a = 0;
            std::cout << "Move Assign: " << s << ", a=" << a << "\n";
        }
        return *this;
    }

这就解决了我的疑惑。我总是认为移动，就是都得移动！一点拷贝都不要沾！实际上是个非常片面、错误的想法。所以，移动构造函数主要利于持有资源的对象（简单理解为指针就行，就是避免把指针指向的东西再拷贝一遍，减少内存开销）。如果对象就只有一堆简单变量而已，那么写的移动构造函数和拷贝构造就没什么区别了。

再回到左右值，右值引用。

我真的很害怕这种文字游戏，用高级概念来解释高级概念，只会让头脑本就不清晰的我变得更笨。

把这些名词放到一遍。本质上，就是编译器对这些地址存放的东西打标记。编译器关心什么呢？它要知道的是：表达式有值类别(value category)以及类型系统附带生命周期信息。

我一开始会把“右值引用”和“右值本身”混为一谈，觉得 T&& 就意味着“这是一个右值”。其实更准确的理解是：右值引用并不是右值本身，而是一种给右值起别名的能力。右值对象通常是临时值，它本身可以直接绑定到右值引用上，例如：

1	A&& r = A();

在编译器眼里，这段代码等价于：先创建了一个临时对象 A()，然后给它取了一个名字 r，于是这个临时对象就有了一个别名。但需要注意的是，这个对象依然被编译器标记为“可被消耗的对象”，也就是允许对它进行资源转移。所以接下来完全可以写：

1	A b = std::move(r);

这意味着右值引用可以捕获一个“将要销毁的对象”，并把这种“可以被破坏性使用”的标记继续传递下去。std::move 的本质其实非常简单，它甚至可以写成这样：

template<class T>
T&& move(T& t) {
    return static_cast<T&&>(t);
}

它并不执行任何移动操作，只是把一个左值转换成右值引用类型，从而告诉编译器允许对它进行移动语义上的优化。真正的移动行为仍然发生在移动构造函数或移动赋值运算符中。

接下来有一个很容易误解的地方：右值引用变量本身是左值。

1
2
3

A&& x = A();
A y = x;            // 这里会调用拷贝
A z = std::move(x); // 这里才会调用移动

原因很简单：只要一个对象有名字，它就被编译器视为可寻址对象，因此具有左值语义；但它的类型却是 T&&，这意味着我们可以显式地把它再转换回右值类别。因此可以总结为：右值引用变量，其实是一个“绑定到右值上的左值”。它只是提供了一条绑定右值的渠道，而不是永久地把该对象钉死为右值。从优化角度看，右值引用最大的价值在于给编译器一个静态承诺：这个对象的生命周期即将结束，因此可以放心地转移资源，避免额外拷贝。

用一句话来说，右值引用代表的是：生命周期和使用方式上的承诺。编译器据此可以跨函数传递“允许破坏源对象”的权限，从而减少堆分配、避免深拷贝、优化容器重分配，并允许在返回大对象时仍然保持零开销。在拷贝构造函数中，编译器必须保证语义不变，因此不能破坏源对象（随便拿到别的对象拥有的资源并改变就是破坏了），只能重新开辟空间并复制内容；而在移动构造函数中，编译器已经得到了“可以破坏源对象”的授权，于是资源可以直接转移，爱怎么破坏就怎么破坏（），源对象只需要被置为空即可。那这么理解右值引用比较好，它把允许破坏源对象这件事情合法化并显式化，同时也给了编译器充分的优化空间。

这个网站好用啊：https://godbolt.org/

写了个测试代码，可以看看汇编在干什么：

#include <iostream>
#include <string>

class A {
public:
    int a;
    std::string s;

    // 普通构造
    A(int la, std::string ls) : a(la), s(std::move(ls)) {
        std::cout << "Construct: " << s << ", a=" << a << "\n";
    }

    // 拷贝构造
    A(const A& other) : a(other.a), s(other.s) {
        std::cout << "Copy Construct: " << s << ", a=" << a << "\n";
    }

    // 移动构造
    A(A&& other) noexcept : a(other.a), s(std::move(other.s)) {
        std::cout << "Move Construct: " << s << ", a=" << a << "\n";
        other.a = 0;
    }

    // 拷贝赋值
    A& operator=(const A& other) {
        if (this != &other) {
            a = other.a;
            s = other.s;
            std::cout << "Copy Assign: " << s << ", a=" << a << "\n";
        }
        return *this;
    }

    // 移动赋值
    A& operator=(A&& other) noexcept {
        if (this != &other) {
            a = other.a;
            s = std::move(other.s);
            other.a = 0;
            std::cout << "Move Assign: " << s << ", a=" << a << "\n";
        }
        return *this;
    }

    ~A() {
        std::cout << "Destruct: " << s << ", a=" << a << "\n";
    }
};

// 返回值测试
A return_by_value() {
    A temp(100, "temp");
    return temp;   // NRVO/移动构造
}

// 返回引用测试
A& return_by_ref(A& obj) {
    return obj;
}

// 返回右值引用测试
A&& return_by_rvalue_ref(A& obj) {
    return std::move(obj);
}

int main() {
    std::cout << "=== 创建 a1 ===\n";
    A a1(1, "a1");

    std::cout << "\n=== 拷贝构造 a2(a1) ===\n";
    A a2(a1);

    std::cout << "\n=== 移动构造 a3(std::move(a1)) ===\n";
    A a3(std::move(a1));

    std::cout << "\n=== 拷贝赋值 a2 = a3 ===\n";
    a2 = a3;

    std::cout << "\n=== 移动赋值 a3 = std::move(a2) ===\n";
    a3 = std::move(a2);

    std::cout << "\n=== 返回值测试 ===\n";
    A a4 = return_by_value();

    std::cout << "\n=== 返回引用测试 ===\n";
    A& ref_a = return_by_ref(a3);
    std::cout << "ref_a.s = " << ref_a.s << "\n";

    std::cout << "\n=== 返回右值引用测试 ===\n";
    A a5 = return_by_rvalue_ref(a3);

    std::cout << "\n=== End of main ===\n";
}

执行结果：

E:\UnrealWorld\project\Learncpp\x64\Debug\Learncpp.exe
=== 创建 a1 ===
Construct: a1, a=1

=== 拷贝构造 a2(a1) ===
Copy Construct: a1, a=1

=== 移动构造 a3(std::move(a1)) ===
Move Construct: a1, a=1

=== 拷贝赋值 a2 = a3 ===
Copy Assign: a1, a=1

=== 移动赋值 a3 = std::move(a2) ===
Move Assign: a1, a=1

=== 返回值测试 ===
Construct: temp, a=100

=== 返回引用测试 ===
ref_a.s = a1

=== 返回右值引用测试 ===
Move Construct: a1, a=1

=== End of main ===
Destruct: a1, a=1
Destruct: temp, a=100
Destruct: , a=0
Destruct: , a=0
Destruct: , a=0

Process finished with exit code 0.

汇编长这样：

# License: MSVC Proprietary
# The use of this compiler is only permitted for internal evaluation purposes and is otherwise governed by the MSVC License Agreement.
# See https://visualstudio.microsoft.com/license-terms/vs2022-ga-community/
$SG35785 DB     'temp', 00H
        ORG $+3
$SG35831 DB     '=== ', 0e5H, 088H, 09bH, 0e5H, 0bbH, 0baH, ' a1 ===', 0aH
        DB      00H
        ORG $+1
$SG35832 DB     'a1', 00H
        ORG $+1
$SG35833 DB     0aH, '=== ', 0e6H, 08bH, 0b7H, 0e8H, 0b4H, 09dH, 0e6H, 09eH
        DB      084H, 0e9H, 080H, 0a0H, ' a2(a1) ===', 0aH, 00H
        ORG $+2
$SG35834 DB     0aH, '=== ', 0e7H, 0a7H, 0bbH, 0e5H, 08aH, 0a8H, 0e6H, 09eH
        DB      084H, 0e9H, 080H, 0a0H, ' a3(std::move(a1)) ===', 0aH, 00H
        ORG $+7
$SG35835 DB     0aH, '=== ', 0e6H, 08bH, 0b7H, 0e8H, 0b4H, 09dH, 0e8H, 0b5H
        DB      08bH, 0e5H, 080H, 0bcH, ' a2 = a3 ===', 0aH, 00H
        ORG $+1
$SG35836 DB     0aH, '=== ', 0e7H, 0a7H, 0bbH, 0e5H, 08aH, 0a8H, 0e8H, 0b5H
        DB      08bH, 0e5H, 080H, 0bcH, ' a3 = std::move(a2) ===', 0aH, 00H
        ORG $+6
$SG35837 DB     0aH, '=== ', 0e8H, 0bfH, 094H, 0e5H, 09bH, 09eH, 0e5H, 080H
        DB      0bcH, 0e6H, 0b5H, 08bH, 0e8H, 0afH, 095H, ' ===', 0aH, 00H
        ORG $+6
$SG35838 DB     0aH, '=== ', 0e8H, 0bfH, 094H, 0e5H, 09bH, 09eH, 0e5H, 0bcH
        DB      095H, 0e7H, 094H, 0a8H, 0e6H, 0b5H, 08bH, 0e8H, 0afH, 095H, ' '
        DB      '===', 0aH, 00H
        ORG $+3
$SG35839 DB     0aH, 00H
        ORG $+6
$SG35840 DB     'ref_a.s = ', 00H
        ORG $+5
$SG35841 DB     0aH, '=== ', 0e8H, 0bfH, 094H, 0e5H, 09bH, 09eH, 0e5H, 08fH
        DB      0b3H, 0e5H, 080H, 0bcH, 0e5H, 0bcH, 095H, 0e7H, 094H, 0a8H, 0e6H
        DB      0b5H, 08bH, 0e8H, 0afH, 095H, ' ===', 0aH, 00H
        ORG $+5
$SG35842 DB     0aH, '=== End of main ===', 0aH, 00H
`string' DB 'Destruct: ', 00H    ; `string'
`string' DB 'Move Assign: ', 00H ; `string'
`string' DB 'Copy Assign: ', 00H ; `string'
`string' DB 'Move Construct: ', 00H ; `string'
`string' DB 'Copy Construct: ', 00H ; `string'
`string' DB 'Construct: ', 00H  ; `string'
`string' DB ', a=', 00H          ; `string'
`string' DB 0aH, 00H                        ; `string'

tv79 = 32
this$ = 64
la$ = 72
ls$ = 80
A::A(int,std::basic_string<char,std::char_traits<char>,std::allocator<char> >) PROC ; A::A, COMDAT
$LN5:
        mov     QWORD PTR [rsp+24], r8
        mov     DWORD PTR [rsp+16], edx
        mov     QWORD PTR [rsp+8], rcx
        sub     rsp, 56                             ; 00000038H
        mov     rax, QWORD PTR this$[rsp]
        mov     ecx, DWORD PTR la$[rsp]
        mov     DWORD PTR [rax], ecx
        mov     rcx, QWORD PTR ls$[rsp]
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> > && std::move<std::basic_string<char,std::char_traits<char>,std::allocator<char> > &>(std::basic_string<char,std::char_traits<char>,std::allocator<char> > &) ; std::move<std::basic_string<char,std::char_traits<char>,std::allocator<char> > &>
        mov     rcx, QWORD PTR this$[rsp]
        add     rcx, 8
        mov     rdx, rax
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >(std::basic_string<char,std::char_traits<char>,std::allocator<char> > &&) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >
        npad    1
        mov     rax, QWORD PTR this$[rsp]
        add     rax, 8
        mov     QWORD PTR tv79[rsp], rax
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR tv79[rsp]
        mov     rdx, rcx
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<char,std::char_traits<char>,std::allocator<char> >(std::basic_ostream<char,std::char_traits<char> > &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::operator<<<char,std::char_traits<char>,std::allocator<char> >
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR this$[rsp]
        mov     edx, DWORD PTR [rcx]
        mov     rcx, rax
        call    QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > & std::basic_ostream<char,std::char_traits<char> >::operator<<(int)
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        npad    1
        mov     rcx, QWORD PTR ls$[rsp]
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> >::~basic_string<char,std::char_traits<char>,std::allocator<char> >(void) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::~basic_string<char,std::char_traits<char>,std::allocator<char> >
        mov     rax, QWORD PTR this$[rsp]
        add     rsp, 56                             ; 00000038H
        ret     0
A::A(int,std::basic_string<char,std::char_traits<char>,std::allocator<char> >) ENDP ; A::A

tv78 = 32
this$ = 64
other$ = 72
A::A(A const &) PROC                                ; A::A, COMDAT
$LN4:
        mov     QWORD PTR [rsp+16], rdx
        mov     QWORD PTR [rsp+8], rcx
        sub     rsp, 56                             ; 00000038H
        mov     rax, QWORD PTR this$[rsp]
        mov     rcx, QWORD PTR other$[rsp]
        mov     ecx, DWORD PTR [rcx]
        mov     DWORD PTR [rax], ecx
        mov     rax, QWORD PTR other$[rsp]
        add     rax, 8
        mov     rcx, QWORD PTR this$[rsp]
        add     rcx, 8
        mov     rdx, rax
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >(std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >
        npad    1
        mov     rax, QWORD PTR this$[rsp]
        add     rax, 8
        mov     QWORD PTR tv78[rsp], rax
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR tv78[rsp]
        mov     rdx, rcx
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<char,std::char_traits<char>,std::allocator<char> >(std::basic_ostream<char,std::char_traits<char> > &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::operator<<<char,std::char_traits<char>,std::allocator<char> >
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR this$[rsp]
        mov     edx, DWORD PTR [rcx]
        mov     rcx, rax
        call    QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > & std::basic_ostream<char,std::char_traits<char> >::operator<<(int)
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        npad    1
        mov     rax, QWORD PTR this$[rsp]
        add     rsp, 56                             ; 00000038H
        ret     0
A::A(A const &) ENDP                                ; A::A

tv80 = 32
this$ = 64
other$ = 72
A::A(A &&) PROC                          ; A::A, COMDAT
$LN4:
        mov     QWORD PTR [rsp+16], rdx
        mov     QWORD PTR [rsp+8], rcx
        sub     rsp, 56                             ; 00000038H
        mov     rax, QWORD PTR this$[rsp]
        mov     rcx, QWORD PTR other$[rsp]
        mov     ecx, DWORD PTR [rcx]
        mov     DWORD PTR [rax], ecx
        mov     rax, QWORD PTR other$[rsp]
        add     rax, 8
        mov     rcx, rax
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> > && std::move<std::basic_string<char,std::char_traits<char>,std::allocator<char> > &>(std::basic_string<char,std::char_traits<char>,std::allocator<char> > &) ; std::move<std::basic_string<char,std::char_traits<char>,std::allocator<char> > &>
        mov     rcx, QWORD PTR this$[rsp]
        add     rcx, 8
        mov     rdx, rax
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >(std::basic_string<char,std::char_traits<char>,std::allocator<char> > &&) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >
        mov     rax, QWORD PTR this$[rsp]
        add     rax, 8
        mov     QWORD PTR tv80[rsp], rax
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR tv80[rsp]
        mov     rdx, rcx
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<char,std::char_traits<char>,std::allocator<char> >(std::basic_ostream<char,std::char_traits<char> > &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::operator<<<char,std::char_traits<char>,std::allocator<char> >
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR this$[rsp]
        mov     edx, DWORD PTR [rcx]
        mov     rcx, rax
        call    QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > & std::basic_ostream<char,std::char_traits<char> >::operator<<(int)
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rax, QWORD PTR other$[rsp]
        mov     DWORD PTR [rax], 0
        mov     rax, QWORD PTR this$[rsp]
        add     rsp, 56                             ; 00000038H
        ret     0
A::A(A &&) ENDP                          ; A::A

tv76 = 32
this$ = 64
other$ = 72
A & A::operator=(A const &) PROC                     ; A::operator=, COMDAT
$LN4:
        mov     QWORD PTR [rsp+16], rdx
        mov     QWORD PTR [rsp+8], rcx
        sub     rsp, 56                             ; 00000038H
        mov     rax, QWORD PTR other$[rsp]
        cmp     QWORD PTR this$[rsp], rax
        je      $LN2@operator
        mov     rax, QWORD PTR this$[rsp]
        mov     rcx, QWORD PTR other$[rsp]
        mov     ecx, DWORD PTR [rcx]
        mov     DWORD PTR [rax], ecx
        mov     rax, QWORD PTR other$[rsp]
        add     rax, 8
        mov     rcx, QWORD PTR this$[rsp]
        add     rcx, 8
        mov     rdx, rax
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> > & std::basic_string<char,std::char_traits<char>,std::allocator<char> >::operator=(std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::operator=
        mov     rax, QWORD PTR this$[rsp]
        add     rax, 8
        mov     QWORD PTR tv76[rsp], rax
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR tv76[rsp]
        mov     rdx, rcx
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<char,std::char_traits<char>,std::allocator<char> >(std::basic_ostream<char,std::char_traits<char> > &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::operator<<<char,std::char_traits<char>,std::allocator<char> >
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR this$[rsp]
        mov     edx, DWORD PTR [rcx]
        mov     rcx, rax
        call    QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > & std::basic_ostream<char,std::char_traits<char> >::operator<<(int)
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        npad    1
$LN2@operator:
        mov     rax, QWORD PTR this$[rsp]
        add     rsp, 56                             ; 00000038H
        ret     0
A & A::operator=(A const &) ENDP                     ; A::operator=

tv79 = 32
this$ = 64
other$ = 72
A & A::operator=(A &&) PROC               ; A::operator=, COMDAT
$LN5:
        mov     QWORD PTR [rsp+16], rdx
        mov     QWORD PTR [rsp+8], rcx
        sub     rsp, 56                             ; 00000038H
        mov     rax, QWORD PTR other$[rsp]
        cmp     QWORD PTR this$[rsp], rax
        je      $LN2@operator
        mov     rax, QWORD PTR this$[rsp]
        mov     rcx, QWORD PTR other$[rsp]
        mov     ecx, DWORD PTR [rcx]
        mov     DWORD PTR [rax], ecx
        mov     rax, QWORD PTR other$[rsp]
        add     rax, 8
        mov     rcx, rax
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> > && std::move<std::basic_string<char,std::char_traits<char>,std::allocator<char> > &>(std::basic_string<char,std::char_traits<char>,std::allocator<char> > &) ; std::move<std::basic_string<char,std::char_traits<char>,std::allocator<char> > &>
        mov     rcx, QWORD PTR this$[rsp]
        add     rcx, 8
        mov     rdx, rax
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> > & std::basic_string<char,std::char_traits<char>,std::allocator<char> >::operator=(std::basic_string<char,std::char_traits<char>,std::allocator<char> > &&) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::operator=
        mov     rax, QWORD PTR other$[rsp]
        mov     DWORD PTR [rax], 0
        mov     rax, QWORD PTR this$[rsp]
        add     rax, 8
        mov     QWORD PTR tv79[rsp], rax
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR tv79[rsp]
        mov     rdx, rcx
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<char,std::char_traits<char>,std::allocator<char> >(std::basic_ostream<char,std::char_traits<char> > &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::operator<<<char,std::char_traits<char>,std::allocator<char> >
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR this$[rsp]
        mov     edx, DWORD PTR [rcx]
        mov     rcx, rax
        call    QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > & std::basic_ostream<char,std::char_traits<char> >::operator<<(int)
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        npad    1
$LN2@operator:
        mov     rax, QWORD PTR this$[rsp]
        add     rsp, 56                             ; 00000038H
        ret     0
A & A::operator=(A &&) ENDP               ; A::operator=

tv71 = 32
this$ = 64
A::~A(void) PROC                                  ; A::~A, COMDAT
$LN4:
        mov     QWORD PTR [rsp+8], rcx
        sub     rsp, 56                             ; 00000038H
        mov     rax, QWORD PTR this$[rsp]
        add     rax, 8
        mov     QWORD PTR tv71[rsp], rax
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR tv71[rsp]
        mov     rdx, rcx
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<char,std::char_traits<char>,std::allocator<char> >(std::basic_ostream<char,std::char_traits<char> > &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::operator<<<char,std::char_traits<char>,std::allocator<char> >
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR this$[rsp]
        mov     edx, DWORD PTR [rcx]
        mov     rcx, rax
        call    QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > & std::basic_ostream<char,std::char_traits<char> >::operator<<(int)
        lea     rdx, OFFSET FLAT:`string'
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        npad    1
        mov     rax, QWORD PTR this$[rsp]
        add     rax, 8
        mov     rcx, rax
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> >::~basic_string<char,std::char_traits<char>,std::allocator<char> >(void) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::~basic_string<char,std::char_traits<char>,std::allocator<char> >
        npad    1
        add     rsp, 56                             ; 00000038H
        ret     0
A::~A(void) ENDP                                  ; A::~A

$T1 = 32
$T2 = 40
tv83 = 48
$T3 = 56
temp$ = 88
__$ArrayPad$ = 128
__$ReturnUdt$ = 160
A return_by_value(void) PROC                 ; return_by_value
$LN7:
        mov     QWORD PTR [rsp+8], rcx
        sub     rsp, 152                      ; 00000098H
        mov     rax, QWORD PTR __security_cookie
        xor     rax, rsp
        mov     QWORD PTR __$ArrayPad$[rsp], rax
        mov     DWORD PTR $T1[rsp], 0
        lea     rax, QWORD PTR $T3[rsp]
        mov     QWORD PTR $T2[rsp], rax
        lea     rdx, OFFSET FLAT:$SG35785
        mov     rcx, QWORD PTR $T2[rsp]
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >(char const * const) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >
        mov     QWORD PTR tv83[rsp], rax
        mov     r8, QWORD PTR tv83[rsp]
        mov     edx, 100                      ; 00000064H
        lea     rcx, QWORD PTR temp$[rsp]
        call    A::A(int,std::basic_string<char,std::char_traits<char>,std::allocator<char> >) ; A::A
        npad    1
        lea     rdx, QWORD PTR temp$[rsp]
        mov     rcx, QWORD PTR __$ReturnUdt$[rsp]
        call    A::A(A &&)             ; A::A
        mov     eax, DWORD PTR $T1[rsp]
        or      eax, 1
        mov     DWORD PTR $T1[rsp], eax
        lea     rcx, QWORD PTR temp$[rsp]
        call    A::~A(void)                     ; A::~A
        mov     rax, QWORD PTR __$ReturnUdt$[rsp]
        mov     rcx, QWORD PTR __$ArrayPad$[rsp]
        xor     rcx, rsp
        call    __security_check_cookie
        add     rsp, 152                      ; 00000098H
        ret     0
A return_by_value(void) ENDP                 ; return_by_value

obj$ = 8
A & return_by_ref(A &) PROC              ; return_by_ref
        mov     QWORD PTR [rsp+8], rcx
        mov     rax, QWORD PTR obj$[rsp]
        ret     0
A & return_by_ref(A &) ENDP              ; return_by_ref

obj$ = 48
A && return_by_rvalue_ref(A &) PROC   ; return_by_rvalue_ref
$LN3:
        mov     QWORD PTR [rsp+8], rcx
        sub     rsp, 40                             ; 00000028H
        mov     rcx, QWORD PTR obj$[rsp]
        call    A && std::move<A &>(A &) ; std::move<A &>
        add     rsp, 40                             ; 00000028H
        ret     0
A && return_by_rvalue_ref(A &) ENDP   ; return_by_rvalue_ref

$T1 = 32
tv165 = 40
ref_a$ = 48
tv148 = 56
$T2 = 64
a3$ = 96
a2$ = 136
a1$ = 176
a5$ = 216
a4$ = 256
__$ArrayPad$ = 296
main    PROC
$LN9:
        sub     rsp, 312                      ; 00000138H
        mov     rax, QWORD PTR __security_cookie
        xor     rax, rsp
        mov     QWORD PTR __$ArrayPad$[rsp], rax
        lea     rdx, OFFSET FLAT:$SG35831
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        npad    1
        lea     rax, QWORD PTR $T2[rsp]
        mov     QWORD PTR $T1[rsp], rax
        lea     rdx, OFFSET FLAT:$SG35832
        mov     rcx, QWORD PTR $T1[rsp]
        call    std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >(char const * const) ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >
        mov     QWORD PTR tv165[rsp], rax
        mov     r8, QWORD PTR tv165[rsp]
        mov     edx, 1
        lea     rcx, QWORD PTR a1$[rsp]
        call    A::A(int,std::basic_string<char,std::char_traits<char>,std::allocator<char> >) ; A::A
        npad    1
        lea     rdx, OFFSET FLAT:$SG35833
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        lea     rdx, QWORD PTR a1$[rsp]
        lea     rcx, QWORD PTR a2$[rsp]
        call    A::A(A const &)           ; A::A
        npad    1
        lea     rdx, OFFSET FLAT:$SG35834
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        lea     rcx, QWORD PTR a1$[rsp]
        call    A && std::move<A &>(A &) ; std::move<A &>
        mov     rdx, rax
        lea     rcx, QWORD PTR a3$[rsp]
        call    A::A(A &&)             ; A::A
        npad    1
        lea     rdx, OFFSET FLAT:$SG35835
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        lea     rdx, QWORD PTR a3$[rsp]
        lea     rcx, QWORD PTR a2$[rsp]
        call    A & A::operator=(A const &)                ; A::operator=
        lea     rdx, OFFSET FLAT:$SG35836
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        lea     rcx, QWORD PTR a2$[rsp]
        call    A && std::move<A &>(A &) ; std::move<A &>
        mov     rdx, rax
        lea     rcx, QWORD PTR a3$[rsp]
        call    A & A::operator=(A &&)          ; A::operator=
        lea     rdx, OFFSET FLAT:$SG35837
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        lea     rcx, QWORD PTR a4$[rsp]
        call    A return_by_value(void)            ; return_by_value
        npad    1
        lea     rdx, OFFSET FLAT:$SG35838
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        lea     rcx, QWORD PTR a3$[rsp]
        call    A & return_by_ref(A &)       ; return_by_ref
        mov     QWORD PTR ref_a$[rsp], rax
        mov     rax, QWORD PTR ref_a$[rsp]
        add     rax, 8
        mov     QWORD PTR tv148[rsp], rax
        lea     rdx, OFFSET FLAT:$SG35840
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        mov     rcx, QWORD PTR tv148[rsp]
        mov     rdx, rcx
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<char,std::char_traits<char>,std::allocator<char> >(std::basic_ostream<char,std::char_traits<char> > &,std::basic_string<char,std::char_traits<char>,std::allocator<char> > const &) ; std::operator<<<char,std::char_traits<char>,std::allocator<char> >
        lea     rdx, OFFSET FLAT:$SG35839
        mov     rcx, rax
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        lea     rdx, OFFSET FLAT:$SG35841
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        lea     rcx, QWORD PTR a3$[rsp]
        call    A && return_by_rvalue_ref(A &) ; return_by_rvalue_ref
        mov     rdx, rax
        lea     rcx, QWORD PTR a5$[rsp]
        call    A::A(A &&)             ; A::A
        npad    1
        lea     rdx, OFFSET FLAT:$SG35842
        mov     rcx, QWORD PTR __imp_std::basic_ostream<char,std::char_traits<char> > std::cout
        call    std::basic_ostream<char,std::char_traits<char> > & std::operator<<<std::char_traits<char> >(std::basic_ostream<char,std::char_traits<char> > &,char const *) ; std::operator<<<std::char_traits<char> >
        npad    1
        lea     rcx, QWORD PTR a5$[rsp]
        call    A::~A(void)                     ; A::~A
        npad    1
        lea     rcx, QWORD PTR a4$[rsp]
        call    A::~A(void)                     ; A::~A
        npad    1
        lea     rcx, QWORD PTR a3$[rsp]
        call    A::~A(void)                     ; A::~A
        npad    1
        lea     rcx, QWORD PTR a2$[rsp]
        call    A::~A(void)                     ; A::~A
        npad    1
        lea     rcx, QWORD PTR a1$[rsp]
        call    A::~A(void)                     ; A::~A
        npad    1
        xor     eax, eax
        mov     rcx, QWORD PTR __$ArrayPad$[rsp]
        xor     rcx, rsp
        call    __security_check_cookie
        add     rsp, 312                      ; 00000138H
        ret     0
main    ENDP

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