Function gelatin::widget_data_ptr

pub fn widget_data_ptr(rc: &Rc<dyn Widget>) -> *const u8

This function can be used to avoid comparing fat trait pointers as those can be different even when they point to the same object. For more see: https://doc.rust-lang.org/std/ptr/fn.eq.html#examples and https://github.com/rust-lang/rust-clippy/pull/5294