C++将引用成员绑定到构造函数参数

https://wandbox.org/ ,带有“g++prog.cc-Wall-Wextra-std=c++1z”):

#include <iostream>

class B{
public:
    B(): copy(false){ std::cout << "B-constructed" << std::endl;}
    B(const B& b): copy(true){ std::cout << "B-copy-constructed" << std::endl; }
    ~B(){ std::cout << (copy?"B-destructed":"B-(copy)-destructed") << std::endl;}

    bool copy;
};

class A{
public:
    A(B b): bref(b){std::cout << "A-constructed" << std::endl;}
    ~A() {std::cout << "A-destructed" << std::endl;}
    B &bref;
};


void f(){
    B b;
    A a(b);

    std::cout << "f over" << std::endl;
}

int main()
{
    f();

    std::cout << "main over" << std::endl;
    return 0;
}

产生以下输出:

B-constructed
B-copy-constructed
A-constructed
B-destructed
f over
A-destructed
B-(copy)-destructed
main over

物体破坏的顺序似乎不同寻常。这就好像构造函数参数的生存期被延长了一样。该标准是否提到将成员引用绑定到构造函数参数?

绑定到mem初始值设定项中引用成员的临时表达式格式错误。[示例:

结构A{

A():v(42){}//错误

常量int&v

};