On Thu, Jan 28, 2016 at 7:57 PM, Michael Marcin
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