Re: [Boost-users] enable_shared_from_this & inheritance

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-10-19 12:26:42

Johan Nilsson wrote:
> 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);

I have no idea why this compiles. It shouldn't, B has two 
enable_shared_from_this<> bases, and the constructor will only initialize 
one of them. Only one of FooA and FooB works (FooA in this case). I'll 
investigate.