Re: Bikeshedding the gnome-class mini-language

[Adrian Perez de Castro <aperez igalia com>]

Hi all,

Jumping into the discussion. Please bear with me knowing that I consider
myself a Rust newbie O:-)

On Wed, 25 Oct 2017 13:20:44 -0500, Federico Mena Quintero <federico gnome org> wrote:
> On Wed, 2017-10-25 at 10:41 +0200, Sebastian Dröge wrote:
>
> [...]
>
> > [...]
> >
> >   #[attributes...]
> >   property some_property: u32 {
> >     get(&self) -> u32 {
> >       self.something
> >     }
> >     set(&self, value: u32) {
> >       self.something = value;
> >     }    
> >   }
> > }
> >
> > Maybe? Not sure about providing the type 3 times, but this way seems
> > most consistent.
>
> Makes sense.  I'll look more closely at Vala.  From it and from C# I
> don't like the magic "value" that it uses inside setters; it appears to
> come from nowhere.
>
> Would "_" make sense just avoid repeating the type?

It can be nice for types with long names. Some shorthand would be nice, but
the underscore is used in Rust for pattern-matching “anything”, and the
matched value gets discarded. An alternative could be allowing the user to
alias the type by using “where”:

  property some_property: T where T: u32 {
          get(&self) -> T {
              self.private().foo
          }
          set(&self, value: T) {
              self.private().foo = value;
          }
  }

> property some_property: u32 {
>     get(&self) -> _ {
>         self.private().foo
>     }
>     set(&self, value: _) {
>         self.private().foo = value;
>     }
> }

For this kind of simple getters... Wouldn't it make sense to provide a way of
“synthesizing” their implementation? Example:

   // The derived/synthesized gettter and setter use the "foo" field
   // of the private struct automatically.
   #[derive(get, set)]
   property foo: u32 { }

   // If one of them needs to do additinal work, only that has to be
   // explicitly implemented.
   #[derive(get)]
   property foo: u32 {
       set(&self, value: u32) {
               self.private().foo = value;
                   self.notify_foo_observers();
           }
   }

Note that I am suggesting that whether a getter/setter exists would still be
explicit, and therefore it remains possible to create properties which only
have a getter or a setter.

BTW, great work on the whole big task of making usage of GObject inside Rust
idiomatic \o/

Cheers,


--
 Adrián 🎩

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