Type parameters better have defaults in the presence of Option

[gkoz]

This

pub fn set_label_widget<T: Upcast<Widget>>(&self, label_widget: Option<&T>)

requires jumping through hoops to pass None:

    x.set_label_widget(None::<Widget>);

There's not much we can do to help it at the moment, because default type parameters don't inform type inference yet. When that is fixed the following signature is going to be more ergonomic;

pub fn set_label_widget<T: Upcast<Widget> = Widget>(&self, label_widget: Option<&T>)

[gkoz]

Apparently, I've jumped the gun on this one. It looks like type parameter defaults on functions are going to be feature gated (rust-lang/rust#27336).

[leoyvens]

What about using trait objects? Isn't the widget is a gtk pointer anyways?

[sdroege]

Trait objects don't work with the IsA trait currently https://github.com/gtk-rs/glib/issues/222

Are type parameter defaults stable now?

[sdroege]

No not stable yet