Re: [Caml-list] RFH: can't figure out why my QT5 widget bindings segfault

[Jonas Jensen <jj@issuu.com>]

On 31 March 2016 at 12:21, Goswin von Brederlow <goswin-v-b@web.de> wrote:
>
> I think it is the only sane way. GUI widgets are full of inheritance
> and you have tons of functions that can take any widget. Without
> objects you would have to use recursive types like
>
>     type t = unit pushButton AbstarctButton.abstractButton Widget.widget Object.oObject OCLass.oClass
>
> (and how do I say that a widget is both an oObject and paintDevice?)
>
> or phantom types like
>
>     type t = [`PushButton | `AbstractButton | `Widget | `Object | `PaintDevice ] OClass.oClass
>
> And that is just for a simple button. Other types would get a lot
> longer, not to mention the type for methods taking other widgets where
> you have multiple of those types.

The phantom-types approach looks attractive. What would be the problem
with it? Obviously, those long types should not be written by hand but
could be aliases, like

type widget = [ `Widget | `Object | `PaintDevice ]
type abstractButton = [ `AbstractButton | widget ]
type pushButton = [ `PushButton | abstractButton ]

And then a handle to a push button would have type "pushButton
oClass". A function taking any widget would have type "[> widget ]
oClass -> ...".