假设 class Owner
有 Member 成员
,它还必须有一个指向它的 const
所有者的 const
指针。该指针在 Owner
的构造函数中提供给 member
,该构造函数接受指向构成 member
的指针作为参数。
考虑 Owner
的构造函数:
using namespace std;
class Owner;
class Member {
friend class Owner;
private:
// this object needs to know its owner for whatever reason
void setOwnership(const Owner* o){
if(owner != nullptr){
throw logic_error("Already owned.");
}
owner = o;
}
const Owner* owner;
};
class Owner {
public:
Owner(Member* m)
: member(move(m))
{
m->setOwnership(this);
}
// need to define copy ctor, move ctor, copy assignment, move assignment, destructor
// because we own member
protected:
const Member* const member;
};
现在我想让 unique_ptr
为我处理 member
的所有权,所以我尝试
class Owner {
public:
// ATTEMPT 1
Owner(unique_ptr<Member> m)
: member(move(m))
{
member->setOwnership(this); // this doesn't work because member points to a const
}
// ATTEMPT 2
Owner(unique_ptr<Member> m){
m->setOwnership(this);
member = move(m); // this doesn't work because member is const
}
protected:
const unique_ptr<const Member> member;
};
Owner
的构造函数的两次尝试都无法编译。我该怎么做呢?原则上似乎没有我不能这样做的理由。
我是否必须为了方便使用 unique_ptr
而牺牲其中一个 const
?
最佳答案
委托(delegate)构造函数来救援:
class Owner {
public:
Owner(std::unique_ptr<Member> m) : Owner(m, m.get()) {}
private:
Owner(unique_ptr<Member>& m, Member* ptr) : member(std::move(m)){
ptr->setOwnership(this);
}
protected:
const std::unique_ptr<const Member> member;
};
关于c++ - 修改 unique_ptr 的目标并用它初始化一个 const unique_ptr,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/33570230/