Are people OK with/prefer the use of owning smart pointers in APIs?
I think smart pointers are great to use for storage, or as struct members
where there's actually a clear need for ownership. Just by virtue of getting
rid of destructors containing single delete expressions this is already a
In many cases there shouldn't be a need for smart pointers at all, because
the object is owned by a central facility's smart pointer so it's safe to
just pass around the pointer in ephemeral contexts like stack-based
instances. In such context raw pointers and references aren't scary --
they're just fine.
There's no contention there - if the pointer is non-owning, there's no
smart pointer to use. Indeed using a smart pointer for a non-owning
pointer would actually break the code by causing double deletes, etc.
Well, shared_ptr notwithstanding - but, yes, choosing between
unique_ptr + non-owning pointers and shared_ptr can sometimes be
non-obvious, but I'm hopeful we generally agree that if there is a
dominating owner they can be given exclusive ownership through a
unique_ptr and everyone else can use raw pointers.
(All the above goes equally for uniquely owned pointers, shared pointers and
intrusive refcounted pointers.)
Are there places where you've found them to be too noisy/burdensome
and would rather use raw pointers or some other abstraction?
A clear place that smart pointers *shouldn't* be used are 'create'
There's already a strong convention in the thousands of 'create' functions
across the codebase and they have the clear, well-defined behaviour of
returning a new pointer.
We all know what to expect from these functions, much like new/delete in C++
and malloc/free. They can be easily adopted by std::shared_ptr or
std::unique_ptr as needed,
They'd actually only ever need to return std::unique_ptr.
std::shared_ptrs can be constructed from xvalue std::unique_ptrs
without any overhead:
std::shared_ptr<T> x = create();
(make_shared has a small allocation (and destruction) benefit that
might sometimes be useful to exploit, of course, but you don't benefit
from that with raw new either, so unique_ptr is no /worse/ off than a
raw implicitly-owning pointer in that regard)
so there's no benefit in enforcing smart pointer usage at creation.
I believe there is. Like const member functions it helps ensure that
ownership is transferred clearly. It's not hard to write bugs like:
T *t = create();
return; // leak
set_thing(t); // transfer ownership here
By making create return a std::unique_ptr, it discourages these kinds
Apart from the complexity and visual clutter, it's pretty annoying to have
to decide whether to get(), release() or somehow else acquire the object you
That generally shouldn't be complicated unless the consumer has weird
ownership semantics, in which case that's worth highlighting.
The result of using smart pointers as returns isn't pretty --
you end up with awkward code like createFoo().get()->func()
This isn't an expression you should need to write, it'd simply be
This is also an expression you shouldn't need to write, it'd simply be
"other = createFoo()". Indeed the alternative here (if createFoo
returns a raw pointer) is "other.reset(createFoo())" which is, imho,
less obvious than simple assignment.
Transfer of new pointers from 'create' functions and usage is already
trivially clear so we shouldn't change these.
The need to use reset rather than assignment and the ease with which
ownership can become uncertain once you leave the create function
don't seem to me to be ideal outcomes.
Ultimately, by moving to a world in which objects are most often
allocated with make_unique (or make_shared) means things like reset,
release, raw new and delete can be given extra scrutiny and memory
management bugs can be better avoided.
For myself, it also just helps me follow/understand code when I can
see ownership explicit in the code rather than having to trace back
through the pointer assignments and function calls.