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 02:48:56

On Thu, Jan 28, 2016 at 7:57 PM, Michael Marcin <mike.marcin_at_[hidden]>
wrote:

> On 1/28/2016 8:09 PM, Emil Dotchevski wrote:
>
>> And it's way too easy to break that guarantee because it's not the
>>> semantics that shared_ptr was designed for.
>>>
>>>
>> {
>>      foo local;
>>      shared_ptr<foo> pl(&local,null_deleter());
>>      ....
>>      do_something(p);
>>      ....
>>      assert(pl.unique());
>> }
>>
>> Yes, in the presence of exceptions one must also assert(pl.unique()) in a
>> catch(...), and yes, compile-time errors are better than run-time errors,
>> but I wouldn't sacrifice the availability of weak_ptr and the capacity of
>> shared_ptr to act as THE single smart pointer framework in a program.
>>
>>
> Why on earth would you ever do this?
>

One reason is to get weak_ptr.

> There is no shared ownership semantics here at all.
>

The point of shared_ptr is to be able to reason that as long as you hold on
to a shared_ptr (which you might get by copying another shared_ptr or by
locking a weak_ptr), the object will not expire, but you don't hold on to
it longer than you need to. This reasoning is perfectly valid within the
scope of do_something.

At any rate, what other use of null_deleter can you think of? Are you
saying that null_deleter makes no sense?

Emil