How do I use unique_ptr for pimpl?

Question

Here is a simplification of what I\'m seeing when I try to use unique_ptr for pimpl. I chose unique_ptr because I really want the class to own the pointer - I want the life

Answer 1

I believe that your test_help.cpp actually sees the ~Help() destructor that you declared default. In that destructor, the compiler tries to generate the unique_ptr destructor, too, but it needs the Impl declaration for that.

So if you move the destructor definition to the Help.cpp, this problem should be gone.

-- EDIT -- You can define the destructor to be default in the cpp file, too:

Help::~Help() = default;

Answer 2

Note this from unique_ptr definition:

std::unique_ptr may be constructed for an incomplete type T, such as to facilitate the use as a handle in the pImpl idiom. If the default deleter is used, T must be complete at the point in code where the deleter is invoked, which happens in the destructor, move assignment operator, and reset member function of std::unique_ptr.