Re: [Boost-users] enable_shared_from_this & inheritance

From: Johan Nilsson (r.johan.nilsson_at_[hidden])
Date: 2006-10-19 09:45:53

Russell Hind wrote:
> I thought each time you inherit from enable_shared_from_this<T> you
> get a new reference count, so with the code below, won't you end up
> with 2 separate reference counts to the same instance?  I thought
> this was a limitation of shared_from_this.

The following passes for me (RC_1_34_0, vc8):

-------
#include <boost/test/auto_unit_test.hpp>
#include <boost/enable_shared_from_this.hpp>

using boost::shared_ptr;
using boost::enable_shared_from_this;

struct A : enable_shared_from_this<A>
{};

struct B : A, enable_shared_from_this<B>
{
    shared_ptr<B> FooB()
    {
        return enable_shared_from_this<B>::shared_from_this();
    }

    shared_ptr<A> FooA()
    {
        return enable_shared_from_this<A>::shared_from_this();
    }
};

BOOST_AUTO_TEST_CASE(EnableSharedFromThisTest)
{
    shared_ptr<B> pB(new B);

    BOOST_REQUIRE_EQUAL(1, pB.use_count());

    {
        shared_ptr<A> pA = pB->FooA();

        BOOST_REQUIRE_EQUAL(2, pB.use_count());
        BOOST_REQUIRE_EQUAL(pB.use_count(), pA.use_count());
    }

    BOOST_REQUIRE_EQUAL(1, pB.use_count());
}

-------------

// Johan