将派生类的unique_ptr用作将unique_ptr用作基类的函数的参数 [英] unique_ptr to a derived class as an argument to a function that takes a unique_ptr to a base class
问题描述
我正在尝试使用 unique_ptr 来在将 unique_ptr 用作基础的函数中派生类类。像这样的东西：
I'm trying to use a unique_ptr to derived class in a function that takes a unique_ptr to a base class. Something like:
class Base {};
class Derived : public Base {};
void f(unique_ptr<Base> const &base) {}
…
unique_ptr<Derived> derived = unique_ptr<Derived>(new Derived);
f(derived);
如果我理解此答案正确，此代码应该可以工作，但是会导致以下编译错误：
If I understand this answer correctly, this code should work, but it causes the following compile errors:
错误C2664： f：无法将参数1从 std :: unique_ptr< _Ty>'转换为'const std :: unique_ptr< _Ty> &’
error C2664: 'f' : cannot convert parameter 1 from 'std::unique_ptr<_Ty>' to 'const std::unique_ptr<_Ty> &'
IntelliSense：从 std :: unique_ptr<派生，std :: default_delete<派生>没有合适的用户定义转换到 const std :: unique_ptr< Base，std :: default_delete< Base>存在
IntelliSense: no suitable user-defined conversion from "std::unique_ptr<Derived, std::default_delete<Derived>>" to "const std::unique_ptr<Base, std::default_delete<Base>>" exists
如果我将 f 更改为 unique_ptr< Derived> const&衍生，它工作正常，但是那不是我想要的。
If I change f to take unique_ptr<Derived> const &derived, it works fine, but that's not what I want.
我做错了吗？我该怎么办才能解决此问题？
Am I doing something wrong? What can I do to work around this?
我正在使用Visual Studio 2012。
I'm using Visual Studio 2012.
推荐答案
您有三个选择：
-
放弃所有权。函数调用后，这将使您的局部变量无法访问动态对象。该对象已转移到被调用方：
Give up ownership. This will leave your local variable without access to the dynamic object after the function call; the object has been transferred to the callee:
f(std::move(derived));
更改 f 的签名：
void f(std::unique_ptr<Derived> const &);
更改变量类型：
Change the type of your variable:
std::unique_ptr<base> derived = std::unique_ptr<Derived>(new Derived);
或者当然只是：
std::unique_ptr<base> derived(new Derived);
甚至：
std::unique_ptr<base> derived = std::make_unique<Derived>();
更新：或者，按照评论的建议，不要完全不转让所有权：
Update: Or, as recommended in the comments, don't transfer ownership at all:
void f(Base & b);
f(*derived);
这篇关于将派生类的unique_ptr用作将unique_ptr用作基类的函数的参数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
