Re: [RFA 3/3] Change counted_command_line to a shared_ptr

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2017-09-02 17:07, Tom Tromey wrote:
> Simon> I looked at this more and found that free_command_lines was 
> indeed
> Simon> being called when the shared_ptr free'd its pointer.  I finally
> Simon> understood that when assigning:
> Simon>   a_shared_ptr = a_unique_ptr;
> Simon> like commands_command_1 does, for example, the deleter is also
> Simon> transferred.
>
> Yeah, I should probably have mentioned that.  I had to read about it
> too, but then I think I had forgotten about it by the time I sent the
> patch.  I don't really understand why unique_ptr and shared_ptr differ
> in this way; if you know the rationale I'd be interested in learning 
> it.

From what I read, unique_ptr accepts its deleter as a template parameter 
so that it results in no overhead compared to a plain pointer.  
shared_ptr already has some overhead, so storing the deleter as a field 
of the control block isn't a big deal.  It makes it more flexible, 
however.  You can for example have a container of shared_ptr that have 
different deleters, which you can't do if the deleter is part of the 
type.

https://stackoverflow.com/questions/27742290/deleter-type-in-unique-ptr-vs-shared-ptr

This series LGTM.

Simon