Code shared from the Rust Playground

playground.rs

#[derive(Debug)]
struct UiState {
    parent: u64,
    id: u64,
}

#[derive(Debug)]
struct Result {
    rect: u64,
}

#[derive(Debug)]
struct UiContext {
    state: UiState,
    result: Result,
}

trait UiContextManager {
    fn ctx_mut(&mut self) -> &mut UiContext;
    fn ctx(&self) -> &UiContext;
    fn state(&mut self) -> &mut UiState { &mut self.ctx_mut().state }
    fn result(&mut self) -> &mut Result { &mut self.ctx_mut().result }
    
    fn enter(&mut self);
    fn exit(&mut self);
}

use core::fmt::Debug;
impl Debug for dyn UiContextManager {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "UiContextManager{{{:?}}}", self.ctx())
    }
}

struct AllocUiContext {
    _ctx: UiContext,
}

impl UiContextManager for AllocUiContext {
    fn ctx_mut(&mut self) -> &mut UiContext { &mut self._ctx }
    fn ctx(&self) -> &UiContext { &self._ctx }

    fn enter(&mut self) {
        
    }
    
    fn exit(&mut self) {
        
    }
}

impl Drop for AllocUiContext {
    fn drop(&mut self) { self.exit(); }
}

trait Ui {
    fn state(&mut self) -> &mut UiState;
    
    fn allocate_ui_with_layout_dyn(&mut self) -> Box<dyn UiContextManager> {
        let state = self.state();
        let child = UiState{id: state.id + 1, parent: state.id};
        let mut ctx = Box::new(AllocUiContext{_ctx: UiContext{state: child, result: Result{rect: 0}}});
        ctx.enter();
        ctx
    }
    
    fn horizontal_with_main_wrap_dyn(&mut self, main_wrap: bool) -> Box<dyn UiContextManager> {
        self.allocate_ui_with_layout_dyn()
    }
    
    fn horizontal(&mut self) -> Box<dyn UiContextManager> {
        self.horizontal_with_main_wrap_dyn(false)
    }
}

impl Ui for UiState {
    fn state(&mut self) -> &mut UiState { self }
}

impl Ui for dyn UiContextManager {
    fn state(&mut self) -> &mut UiState { &mut self.ctx_mut().state }
}

fn main() {
    let mut root = UiState{parent: 0, id: 0};
    println!("root {:?}", root);
    {
        let mut ui = root.horizontal();
        println!("ui 1 {:?}", ui);
        {
            let mut ui = ui.horizontal();
            println!("ui 2 {:?}", ui);
        }
    }
}