Frank Mori Hess <frank.hess@nist.gov> writes:
On Monday 29 November 2010, Ansel Sermersheim wrote:
After mulling this over for some time, I _think_ I have come up with a solution that mitigates all these problems.
I have a new patch up, at the same URL. In order to make this mechanism work, I had to add a new constructor to boost::shared_ptr<T>, which I am loath to do. Given that downside the patch appears to work properly. It also adds a free function boost::shared_from<T>(T*) which returns a boost::shared_ptr<T>.
The only cast that occurs in this code is a static_cast that downcasts from enable_shared_from_polymorphic<T> to T. I have read the relevant portions of the standard several times and I beleive this is valid, but I would definitely be curious if wiser heads agree with my reading.
If you use a free function only (see enable_shared_from_raw.hpp in trunk), the enabling base class doesn't have to use the CRTP.
That is true. However, part of my goal was to create a drop-in replacement for enable_shared_from_this which will work even when multiple classes in the inheritance heirarchy inherit from it. Thus, shared_from_this() needs to know what type to return. It certainly would be possible to have another type that inherits from enable_shared_from_polymorphic_base, which would then allow use of the free function. Or the free function may not be the most desirable interface. An earlier version had shared_from as a method, so that one could only call it as shared_from(this). I haven't really thought through the pros and cons of free function vs method at this point.
Why did you need another shared_ptr constructor (sorry, I don't have time to actually read the code)? It's hard to imagine, given the presence of the shared_ptr aliasing constructor.
Now why on earth didn't I see that the last time I looked at the available shared_ptr constructors? That is exactly what was needed. This removes one of my major dislikes about this approach. I will respin a new patch later today and clean up this area. Thank you very much for the critique, Ansel