Re: [libgpiod][RFC PATCH] bindings: cxx: demote the line's parent chip reference to a weak_ptr

[Helmut Grohne <helmut.grohne@intenta.de>]

On Mon, Oct 19, 2020 at 03:06:18PM +0200, Bartosz Golaszewski wrote:
> But this still forces us to do
> 
>     return chip(::std::shared_ptr<::gpiod_chip>(this->_m_owner));
> 
> instead of a much more elegant
> 
>     return chip(this->_m_owner);
> 
> in line.cpp and there's an even less elegant thing in iter.cpp. Or am
> I missing something?

I confirm the behaviour you see. My intuition that the conversion would
happen implicitly was wrong.

Still the sticking point is this: Your constructor should allow for most
flexibility to the caller and in this case that means it should consume
a shared_ptr by value.

In order to make the case with a weak_ptr bearable, I suggest adding a
delegating constructor:

    chip(const ::std::weak_ptr<::gpiod_chip>& chip_ptr) :
        chip(::std::shared_ptr<::gpiod_chip>(chip_ptr)) {}

That way your desired way of calling should continue to work while not
forcing callers to convert a real shared_ptr to weak_ptr and back.

Sorry for the confusion about this.

Helmut