Компоновщик на Rust
Компоновщик — это структурный паттерн, который позволяет создавать дерево объектов и работать с ним так же, как и с единичным объектом.
Компоновщик давно стал синонимом всех задач, связанных с построением дерева объектов. Все операции компоновщика основаны на рекурсии и «суммировании» результатов на ветвях дерева.
Files and Folders
Let’s try to understand the Composite pattern with an example of an operating system’s file system. In the file system, there are two types of objects: files and folders. There are cases when files and folders should be treated to be the same way. This is where the Composite pattern comes in handy.
File and Directory are both of the trait Component with a single search method. For a file, it will just look into the contents of the file; for a folder, it will go through all files of that folder to find that keyword.
fs/mod.rs
mod file;
mod folder;
pub use file::File;
pub use folder::Folder;
pub trait Component {
fn search(&self, keyword: &str);
}
fs/file.rs
use super::Component;
pub struct File {
name: &'static str,
}
impl File {
pub fn new(name: &'static str) -> Self {
Self { name }
}
}
impl Component for File {
fn search(&self, keyword: &str) {
println!("Searching for keyword {} in file {}", keyword, self.name);
}
}
fs/folder.rs
use super::Component;
pub struct Folder {
name: &'static str,
components: Vec<Box<dyn Component>>,
}
impl Folder {
pub fn new(name: &'static str) -> Self {
Self {
name,
components: vec![],
}
}
pub fn add(&mut self, component: impl Component + 'static) {
self.components.push(Box::new(component));
}
}
impl Component for Folder {
fn search(&self, keyword: &str) {
println!(
"Searching recursively for keyword {} in folder {}",
keyword, self.name
);
for component in self.components.iter() {
component.search(keyword);
}
}
}
main.rs
mod fs;
use fs::{Component, File, Folder};
fn main() {
let file1 = File::new("File 1");
let file2 = File::new("File 2");
let file3 = File::new("File 3");
let mut folder1 = Folder::new("Folder 1");
folder1.add(file1);
let mut folder2 = Folder::new("Folder 2");
folder2.add(file2);
folder2.add(file3);
folder2.add(folder1);
folder2.search("rose");
}
Output
Searching recursively for keyword rose in folder Folder 2 Searching for keyword rose in file File 2 Searching for keyword rose in file File 3 Searching recursively for keyword rose in folder Folder 1 Searching for keyword rose in file File 1 ------------------------------------
