API discrepancy about egui HOT 1 OPEN

You are right in pointing this out, and I haven't quite converged on a final design here, but there is actually some method to the madness.

There are two fundamental categories in Egui:

• Widgets: buttons, sliders, etc. You use a builder pattern to construct them, and then you add them to a ui, e.g. ui.add(Label::new("Hello world")).

• Containers: things that wrap code that adds widgets. Examples are ScrollArea, Resize, Frame, CollapsingHeader and Window (which is a wrapper around the four previous ones). Containers need to execute some custom code to add the contents. They follow the form Container::new(...).builder(...).show(ui, |ui| {...})

Since you never run any custom closure for e.g. Label, there makes no sense to unify Widgets and Containers. So that covers your Button and Window examples.

As for ui.collapsing: this is part of a few shortcut functions. Others include ui.button("Click me"), ui.label("Hello world"), ui.checkbox(...) and ui.radio(...). It is a bit inconsistent, but it is so much nicer to write if ui.button("OK").clicked than ui.add(Button::new("OK")).clicked. If Rust supported default, named arguments, this is the way I would design all widgets (instead of using the rather verbose builder pattern).

As for Menu: that was something I threw together pretty quickly. It should probably be refactored into a Container.

from egui.