dynamic_cast with unique_ptr

dynamiccastunique.cpp

#include <iostream>
#include <memory>

struct A
{
	virtual ~A() {}
};

struct B : public A
{
	
};

int main()
{
	std::unique_ptr<B> b(new B);
	std::unique_ptr<A> a(b.release());

	std::unique_ptr<A> a1(new B);
	std::unique_ptr<B> b1(dynamic_cast<B*>(a1.release()));

	// Error
	//std::unique_ptr<A> a2(new B);
	//std::unique_ptr<B> b2(a1.release());

	return 0;
}

I came to the same conclusion, thanks :)

This leaks memory.

@MaxKellermann where, and how would you improve it?

If the dynamic_cast fails, it returns nullptr, means b1 is not set, but a1 has already been released, and the object previously pointed-to by a1 is owned by nobody, and thus leaks.
Cast first, and only if it succeeds you may release a1.

Yeah OK, so in general this approach could leak, that's true.
Thanks for the clarification.