std::unique_ptr + destructor = creatable constraint not satisfied

[victl]

Expected Behavior

The following code should compile:

#include <memory>
#include "di.hpp"

namespace di = boost::di;

class A
{
  std::unique_ptr<int> val_;

public:
  explicit A(std::unique_ptr<int> val) : val_(std::move(val)) {}
  ~A() {}
};

int main(int argc, const char *argv[])
{
  auto a = di::make_injector().create<A>();
}

Actual Behavior

Won't compile. However, if you comment out the destructor ~A(){}, then it compiles correctly.

Am I using std::unique_ptr incorrectly?

Complete error output from MSVC can be found HERE

Specifications

• Version: commit 8e02462
• Platform: Win10 & Ubuntu 16.04
• Subsystem: MSVC 14.24.28314, and g++ 5.4.0

[victl]

I've figured out that when your class have unique_ptr, then a direct instance can't be created by boost-di, because the copy constructor is implicitly deleted. I suppose the create<A>() method is triggering a copy action somewhere inside. Everything making sense to me, except the fact that if you comment out the destructor it compiles.

For a workaround, I can create<std::unique_ptr<A>>() instead.

[krzysztof-jusiak]

Thanks, @victl. You are right, in that case defining the destructor requires the move.

You can do it by using rvalue ref or creating std::unique_ptr to avoid deleted copies.

int main() {
  [[maybe_unused]] auto&& a = di::make_injector().create<A&&>();
}

Full example here -> https://wandbox.org/permlink/V7Ap9C4YtfkFAGva

[victl]

@krzysztof-jusiak I have tried this method in my actual project with more complicated codes, I can't create rvalue references or unique_ptr either. Same problem: can't have destructor, compiles well without it. Can you explain why the destructor matters here?

[kanstantsin-chernik]

Hi. Check this out. I remember I have already answered this question. https://github.com/boost-experimental/di/issues/428