lifetime.rs

use iced::{button, Align, Button, Column, Element, Sandbox, Settings, Text};

pub fn main() {
    App::run(Settings::default())
}

#[derive(Default)]
struct First<'value> {
    value: &'value str,
}

#[derive()]
struct Second<'value> {
    value: &'value str,
}

enum Step<'value> {
    First(First<'value>),
    Second(Second<'value>),
}

struct App<'value> {
    value: String,
    step: Step<'value>,
    toggle_button: button::State,
}

#[derive(Debug, Clone, Copy)]
enum Message {
    Toggle,
}

impl<'value> Sandbox for App<'_> {
    type Message = Message;

    fn new() -> Self {
        let value = String::from("Hello");
        Self {
            value,
            step: Step::First(First { value: &value }),
            toggle_button: button::State::new(),
        }
    }

    fn title(&self) -> String {
        String::from("Lifetimes")
    }

    fn update(&mut self, message: Message) {
        match message {
            Message::Toggle => match self.step {
                Step::First(_) => {
                    let second = Second { value: &self.value };
                    self.step = Step::Second(second);
                }
                Step::Second(_) => {
                    let first = First { value: &self.value };
                    self.step = Step::First(first);
                }
            },
        }
    }

    fn view(&mut self) -> Element<Message> {
        Column::new()
            .padding(20)
            .align_items(Align::Center)
            .push(
                Button::new(&mut self.toggle_button, Text::new("Toggle")).on_press(Message::Toggle),
            )
            .push(match self.step {
                Step::First(first) => Text::new(format!("first ... value={}", first.value)),
                Step::Second(second) => Text::new(format!("second ... value={}", second.value)),
            })
            .into()
    }
}