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Міст на Rust

Міст — це структурний патерн, який розділяє бізнес-логіку або великий клас на кілька окремих ієрархій, які можна розвивати далі окремо одну від одної.

Одна з цих ієрархій (абстракція) отримає посилання на об’єкти іншої ієрархії (реалізація) і буде делегувати їм основну роботу. Завдяки тому, що всі реалізації будуть дотримуватись спільного інтерфейсу, їх можна буде взаємозамінювати всередині абстракції.

Devices and Remotes

This example illustrates how the Bridge pattern can help divide the monolithic code of an app that manages devices and their remote controls. The Device classes act as the implementation, whereas the Remotes act as the abstraction.

remotes/mod.rs

mod advanced;
mod basic;

pub use advanced::AdvancedRemove;
pub use basic::BasicRemote;

use crate::device::Device;

pub trait HasMutableDevice<D: Device> {
    fn device(&mut self) -> &mut D;
}

pub trait Remote<D: Device>: HasMutableDevice<D> {
    fn power(&mut self) {
        println!("Remote: power toggle");
        if self.device().is_enabled() {
            self.device().disable();
        } else {
            self.device().enable();
        }
    }

    fn volume_down(&mut self) {
        println!("Remote: volume down");
        let volume = self.device().volume();
        self.device().set_volume(volume - 10);
    }

    fn volume_up(&mut self) {
        println!("Remote: volume up");
        let volume = self.device().volume();
        self.device().set_volume(volume + 10);
    }

    fn channel_down(&mut self) {
        println!("Remote: channel down");
        let channel = self.device().channel();
        self.device().set_channel(channel - 1);
    }

    fn channel_up(&mut self) {
        println!("Remote: channel up");
        let channel = self.device().channel();
        self.device().set_channel(channel + 1);
    }
}

remotes/basic.rs

use crate::device::Device;

use super::{HasMutableDevice, Remote};

pub struct BasicRemote<D: Device> {
    device: D,
}

impl<D: Device> BasicRemote<D> {
    pub fn new(device: D) -> Self {
        Self { device }
    }
}

impl<D: Device> HasMutableDevice<D> for BasicRemote<D> {
    fn device(&mut self) -> &mut D {
        &mut self.device
    }
}

impl<D: Device> Remote<D> for BasicRemote<D> {}

remotes/advanced.rs

use crate::device::Device;

use super::{HasMutableDevice, Remote};

pub struct AdvancedRemove<D: Device> {
    device: D,
}

impl<D: Device> AdvancedRemove<D> {
    pub fn new(device: D) -> Self {
        Self { device }
    }

    pub fn mute(&mut self) {
        println!("Remote: mute");
        self.device.set_volume(0);
    }
}

impl<D: Device> HasMutableDevice<D> for AdvancedRemove<D> {
    fn device(&mut self) -> &mut D {
        &mut self.device
    }
}

impl<D: Device> Remote<D> for AdvancedRemove<D> {}

device/mod.rs

mod radio;
mod tv;

pub use radio::Radio;
pub use tv::Tv;

pub trait Device {
    fn is_enabled(&self) -> bool;
    fn enable(&mut self);
    fn disable(&mut self);
    fn volume(&self) -> u8;
    fn set_volume(&mut self, percent: u8);
    fn channel(&self) -> u16;
    fn set_channel(&mut self, channel: u16);
    fn print_status(&self);
}

device/radio.rs

use super::Device;

#[derive(Clone)]
pub struct Radio {
    on: bool,
    volume: u8,
    channel: u16,
}

impl Default for Radio {
    fn default() -> Self {
        Self {
            on: false,
            volume: 30,
            channel: 1,
        }
    }
}

impl Device for Radio {
    fn is_enabled(&self) -> bool {
        self.on
    }

    fn enable(&mut self) {
        self.on = true;
    }

    fn disable(&mut self) {
        self.on = false;
    }

    fn volume(&self) -> u8 {
        self.volume
    }

    fn set_volume(&mut self, percent: u8) {
        self.volume = std::cmp::min(percent, 100);
    }

    fn channel(&self) -> u16 {
        self.channel
    }

    fn set_channel(&mut self, channel: u16) {
        self.channel = channel;
    }

    fn print_status(&self) {
        println!("------------------------------------");
        println!("| I'm radio.");
        println!("| I'm {}", if self.on { "enabled" } else { "disabled" });
        println!("| Current volume is {}%", self.volume);
        println!("| Current channel is {}", self.channel);
        println!("------------------------------------\n");
    }
}

device/tv.rs

use super::Device;

#[derive(Clone)]
pub struct Tv {
    on: bool,
    volume: u8,
    channel: u16,
}

impl Default for Tv {
    fn default() -> Self {
        Self {
            on: false,
            volume: 30,
            channel: 1,
        }
    }
}

impl Device for Tv {
    fn is_enabled(&self) -> bool {
        self.on
    }

    fn enable(&mut self) {
        self.on = true;
    }

    fn disable(&mut self) {
        self.on = false;
    }

    fn volume(&self) -> u8 {
        self.volume
    }

    fn set_volume(&mut self, percent: u8) {
        self.volume = std::cmp::min(percent, 100);
    }

    fn channel(&self) -> u16 {
        self.channel
    }

    fn set_channel(&mut self, channel: u16) {
        self.channel = channel;
    }

    fn print_status(&self) {
        println!("------------------------------------");
        println!("| I'm TV set.");
        println!("| I'm {}", if self.on { "enabled" } else { "disabled" });
        println!("| Current volume is {}%", self.volume);
        println!("| Current channel is {}", self.channel);
        println!("------------------------------------\n");
    }
}

main.rs

mod device;
mod remotes;

use device::{Device, Radio, Tv};
use remotes::{AdvancedRemove, BasicRemote, HasMutableDevice, Remote};

fn main() {
    test_device(Tv::default());
    test_device(Radio::default());
}

fn test_device(device: impl Device + Clone) {
    println!("Tests with basic remote.");
    let mut basic_remote = BasicRemote::new(device.clone());
    basic_remote.power();
    basic_remote.device().print_status();

    println!("Tests with advanced remote.");
    let mut advanced_remote = AdvancedRemove::new(device);
    advanced_remote.power();
    advanced_remote.mute();
    advanced_remote.device().print_status();
}

Output

Tests with basic remote.
Remote: power toggle
------------------------------------
| I'm TV set.
| I'm enabled
| Current volume is 30%
| Current channel is 1
------------------------------------

Tests with advanced remote.
Remote: power toggle
Remote: mute
------------------------------------
| I'm TV set.
| I'm enabled
| Current volume is 0%
| Current channel is 1
------------------------------------

Tests with basic remote.
Remote: power toggle
------------------------------------
| I'm radio.
| I'm enabled
| Current volume is 30%
| Current channel is 1
------------------------------------

Tests with advanced remote.
Remote: power toggle
Remote: mute
------------------------------------
| I'm radio.
| I'm enabled
| Current volume is 0%
| Current channel is 1
------------------------------------```

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