I'm working out how to wrap egui's API for my scripting language. Something that would make this a lot easier is if there was an alternative API to the functions that take callbacks (like SidePanel::show, Window::show, and Ui::horizontal) which could be written in straight-line code. For example, an object that exposes a &mut UI to draw widgets, and has a finish method which drops it.

It looks like I can emulate this with some pairs of Ui::new and Ui::allocate_rect, but I'll have to rewrite all the useful stuff those functions do.