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: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2016-01-29 16:27:01

On Fri, Jan 29, 2016 at 11:24 AM, Rob Stewart <rob.stewart_at_[hidden]>
wrote:

> I understand that full well. The example that Emil presented can easily
> lead to having shared_ptrs that refer to release stack memory.
>

My original example was:

{
     foo local;
     shared_ptr<foo> pl(&local,null_deleter());
     ....
     do_something(p);
     ....
     assert(pl.unique());
}

What if I change it to:

int main()
{
     foo local;
     shared_ptr<foo> pl(&local,null_deleter());
     ....
     do_something(p);
     ....
     assert(pl.unique());
}

Does it look less scary now?

It seems that you guys look at this as "why would do_something take a
shared_ptr if it can't keep a copy of it". Being able to retain a copy of
the shared_ptr is one reason, yes. The other reason is that do_something
needs to make sure that the object doesn't expire before it returns, which
in this case it doesn't.

Further, what if do_something is declared as:

void do_something( weak_ptr<foo> const & );

Now it's not that it'll keep shared_ptr references after it returns, but
it'll be creating and destroying shared_ptrs as needed, to make sure that
the object doesn't expire while it's being used. Which, again, in this case
it doesn't.

Emil