[Development] Views in APIs

[Jean-Michaël Celerier]

> To have type-erased containers, we need to go back to something like
java.lang.Collection.

C++20 offers coroutines which allows the same things without java-like type
hierarchies though
(and with much more flexibility as you don't even need to have an actual
container existing somewhere - your function's stack
can serve as one just fine :p).

see e.g. https://godbolt.org/z/cEv7Gp - in simple cases it optimizes as
well as as a std::vector.

Well, for Qt 7 maybe :-)


On Thu, May 14, 2020 at 9:00 PM Thiago Macieira <thiago.macieira at intel.com>
wrote:

> On Thursday, 14 May 2020 02:33:43 PDT Marc Mutz via Development wrote:
> > On 2020-05-14 02:15, Thiago Macieira wrote:
> > > On quarta-feira, 13 de maio de 2020 01:41:26 PDT Иван Комиссаров wrote:
> > >> std::span<Product> Project::productsSpan() const & { return
> > >> d->products; }
> > >> std::span<Product> Project::productsSpan() const && = delete;
> > >
> > > Now implement either or both of these functions if internally you have
> > > a
> > > QSet<Products>.
> >
> > Now implement QHash<Qt::ItemRole, QByteArray> roleNames() when
> > internally you have a std::pmr::unordered_map<Qt::ItemRole,
> > std::pmr::string>, with all the data allocated from one
> > std::pmr::monotonic_buffer_resource.
> >
> > This does both ways.
>
> No, it doesn't. In both you created a copy on demand.
>
> But you can only *return* said copy if the return type is an owning
> container.
> std::span and the views are not.
>
> > And: you can also have views over associated data structures, they just
> > can't have inline functions because they need to type-erase the
> > container. For an extreme example, consider QAssociativeIterable.
>
> Which is:
> a) a horrible API
> b) misspelling "iteratable"
>
> To have type-erased containers, we need to go back to something like
> java.lang.Collection.
>
> --
> Thiago Macieira - thiago.macieira (AT) intel.com
>   Software Architect - Intel System Software Products
>
>
>
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