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Subject: Re: [std-proposals] Ptr proposal: looking for feedback
From: Jason McKesson (jmckesson_at_[hidden])
Date: 2020-07-18 10:15:29


On Sat, Jul 18, 2020 at 8:43 AM Lyberta via Std-Proposals
<std-proposals_at_[hidden]> wrote:
>
> Ville Voutilainen via Std-Proposals:
> > On Fri, 17 Jul 2020 at 17:40, Arthur O'Dwyer <arthur.j.odwyer_at_[hidden]> wrote:
> >> But if that were actually the only use-case, then we wouldn't need ptr<T> at all! There's already an idiomatic C++ way of doing that:
> >> void betterfunc(Foo& f);
> >> ... betterfunc(local); ... // no ownership
> >> ... betterfunc(*std::make_unique<Foo>(42)); // construct an owning unique_ptr, and then deallocate it afterward
> >> If the parameter `Foo& f` were const-qualified, we could even do this:
> >> ... betterfunc(Foo(42)); ... // construct a Foo and deallocate it afterward, without even using the heap!
> >
> > ..but if the parameter of betterfunc is supposed to be nullable, none
> > of that nonsense works.
>
> This is exactly why we need std::optional<T&> in the standard.

Or you can just pass a `T*`. I know some people don't like that idea
because "ownership semantics are unclear", but they are clear by
convention: naked pointers have no ownership of what they point to.
The end.

Or if you absolutely *must* represent such non-ownership, then you can
use `observer_ptr<T>`.


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