使用 pimpl 移动类无法编译
Move of class with pimpl won't compile
在下面的例子中,怎么可能正确调用~CImpl,但是当需要移动类时,编译器说它有一个不完整的类型?
如果将 Impl 的声明移动到它工作的标头,我的问题是为什么析构函数被称为 fine,所以看起来类型并不完整,但在移动时出现问题。
文件: C.hpp
#include <memory>
class Impl;
class C
{
public:
C();
~C();
C(C&&) = default;
C& operator=(C&&) = default;
std::unique_ptr<Impl> p;
};
文件 C.cpp
#include "C.hpp"
#include <iostream>
using namespace std;
class Impl
{
public:
Impl() {}
virtual ~Impl() = default;
virtual void f() = 0;
};
class CImpl: public Impl
{
public:
~CImpl()
{
cout << "~CImpl()" << endl;
}
void f()
{
cout << "f()" << endl;
}
};
C::C():
p(new CImpl())
{}
C::~C()
文件:主.cpp
#include <iostream>
#include <vector>
#include "C.hpp"
using namespace std;
int main(int argc, char *argv[])
{
vector<C> vc;
// this won't compile
//vc.emplace_back(C());
C c;
C c2 = move(c); // this won't compile
}
编译器输出:
+ clang++ -std=c++11 -Wall -c C.cpp
+ clang++ -std=c++11 -Wall -c main.cpp
In file included from main.cpp:3:
In file included from ./C.hpp:1:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/memory:80:
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/unique_ptr.h:65:16: error: invalid application of 'sizeof' to an incomplete type 'Impl'
static_assert(sizeof(_Tp)>0,
^~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/unique_ptr.h:184:4: note: in instantiation of member function
'std::default_delete<Impl>::operator()' requested here
get_deleter()(__ptr);
^
./C.hpp:12:5: note: in instantiation of member function 'std::unique_ptr<Impl, std::default_delete<Impl> >::~unique_ptr' requested here
C(C&&) = default;
^
./C.hpp:3:7: note: forward declaration of 'Impl'
class Impl;
^
1 error generated.
析构函数工作正常,因为析构函数的(空)主体位于 C 源文件中,可以访问 Impl
的完整定义。但是,移动构造函数和移动赋值在标头中是默认(定义的),没有定义Impl
。
您可以做的是在标头中C(C&&);
,在源文件中C::C(C&&) = default;
。