Re: [boost] [smart_ptr] Interest in the missing smart pointer (that can target the stack)

Subject: Re: [boost] [smart_ptr] Interest in the missing smart pointer (that can target the stack)
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2016-01-28 21:07:38

On 29/01/2016 14:07, Nat Goodspeed wrote:
> Do you mean, for example, that you can create a registered_ptr to an
> instance within the constructor? (I haven't looked at your
> implementation.)

FWIW, you can do that with enable_shared_from_raw, provided that you can 
guarantee that someone will create a shared_ptr from the result of the 
construction.  (Otherwise you get a memory leak.)

> Heh. I've wished for some time for the ability to constrain a class:
> "this cannot be static" or "this cannot be instantiated on the stack"
> or "this cannot be instantiated on the heap." But I've never been
> sufficiently motivated to write a proposal -- or, come to that, search
> through WG21 archives for an existing proposal.

You can do "this cannot be instantiated on the stack" fairly easily -- 
make a private constructor with a static factory method that returns a 
unique_ptr or shared_ptr.

In the latter case, this is also a good way to guarantee that a given 
class has shared ownership, for use with enable_shared_from_this or as 
an alternate method for the above to create pointers outside the "real" 
constructor while still inside the "perceived" constructor.