Re: [Boost-users] enable_shared_from_this()

Subject: Re: [Boost-users] enable_shared_from_this()
From: John M. Dlugosz (mpbecey7gu_at_[hidden])
Date: 2013-02-07 03:57:40

On 2/5/2013 9:43 AM, boost-users-request-at-lists.boost.org |Boost/Allow to home| wrote:

From: Dominique Devienne<ddevienne_at_[hidden]>

> Thanks for any insight on this. Could very well be I'm missing
> something obvious (my C++ expertise doesn't rise to Boost levels), but
> so far I fail to see the drawbacks.
My old smart pointers (dating back to the '90's) had full support for initializing a smart 
pointer from a raw pointer even if it was already known to the smart pointer system. It 
was one of six _essential_ features (I called it “lost and found”) and I agree there were 
no troubles with it. It is easy to do when the class is derived from a helper base (like 
enable_shared_from_this does) and furthermore it doesn't need the CRTP.

I agree that an extension to the now-standard enable_self_from_this could be implemented 
that gives a self_from_this that may be called during the constructor or as the first way 
to obtain a shared_ptr, also provide for "lost and found" usage, and not behave 
differently for any usage that is well-formed using the standard class (that is, it would 
be a pure extension).

When changing some existing code to use shared_ptr, I've wished something like that was 
available, and missed my old class in this respect. For new code, in general use a Create 
static member that wraps the call to the (private) constructor so you can't create 
anything other than a shared_ptr, and the stuff that needs the shared ptr during 
"construction" gets moved to the stage 2, in the body of Create. In particular, if the 
object registers itself with collaborators (via shared pointers) you really wanted that 
part _in_ the constructor.

—John