[FEATURE REQUEST] Properties macro doesn't check for equality

[BrainBlasted]

Usually setters for GObject properties check new values for equality and return if the value is equal to the current value. This is to prevent over notifying.

[sdroege]

This will have to be opt-in as not every value is comparable in a useful way, and you probably also want to be able to provide a custom equality function to not e.g. compare GInetAddresses by pointer but by value.

Do you have a suggestion how the API could look like?

[BrainBlasted]

How about:

// Uses `Eq/PartialEq`
#[property(get, set, check_eq)]
pub child: RefCell<Option<gtk::Widget>>,
// Uses custom function that takes two of `T`
#[property(get, set, check_eq = compare_address)]
pub ip: RefCell<Option<gio::InetAddress>>

[sdroege]

I think having something in the name about notification would be useful. The only difference in behaviour is that it would do a comparison and only notify if the comparison fails.

[sdroege]

CC @ranfdev

[ranfdev]

I agree it's needed, I'm just not convinced about the API. In the meantime it can be implemented by the user using a custom macro set_if_changed!

#[properties(get, set = set_if_changed!(ip), explicit_notify)]
pub ip: RefCell<Option<gio::InetAddress>>

set_if_changed! can take advantage of the trait PropertySet to write inside a property. It would wrap PropertySet::set and check for equality before calling the method.

[ranfdev]

There you go, it should cover 99% of the gtk use cases.

macro_rules! set_if_changed {
    ($ident:ident) => {
        |this: &&Self, val| {
            if glib::PropertyGet::get(&this.$ident, |old_val| old_val == &val) {
                return;
            }
            glib::PropertySet::set(&this.$ident, val);
            this.obj().notify(stringify!($ident));
        }

    }
}

struct MyStruct {
  #[properties(get, set = set_if_changed!(ip), explicit_notify)]
  pub ip: RefCell<Option<gio::InetAddress>>
}

[SeaDve]

This unfortunately is problematic on properties with -