Rust 迭代器模式讲解和代码示例

let users = UserCollection::new(); let mut iterator = users.iter(); iterator.next(); 

impl Iterator for UserIterator<'_> { fn next(&mut self) -> Option<Self::Item>; } 

pub struct UserCollection { users: [&'static str; 3], } /// A custom collection contains an arbitrary user array under the hood. impl UserCollection { /// Returns a custom user collection. pub fn new() -> Self { Self { users: ["Alice", "Bob", "Carl"], } } /// Returns an iterator over a user collection. /// /// The method name may be different, however, `iter` is used as a de facto /// standard in a Rust naming convention. pub fn iter(&self) -> UserIterator { UserIterator { index: 0, user_collection: self, } } } /// UserIterator allows sequential traversal through a complex user collection /// without exposing its internal details. pub struct UserIterator<'a> { index: usize, user_collection: &'a UserCollection, } /// `Iterator` is a standard interface for dealing with iterators /// from the Rust standard library. impl Iterator for UserIterator<'_> { type Item = &'static str; /// A `next` method is the only `Iterator` trait method which is mandatory to be /// implemented. It makes accessible a huge range of standard methods, /// e.g. `fold`, `map`, `for_each`. fn next(&mut self) -> Option<Self::Item> { if self.index < self.user_collection.users.len() { let user = Some(self.user_collection.users[self.index]); self.index += 1; return user; } None } } 

use crate::users::UserCollection; mod users; fn main() { print!("Iterators are widely used in the standard library: "); let array = &[1, 2, 3]; let iterator = array.iter(); // Traversal over each element of the array. iterator.for_each(|e| print!("{} ", e)); println!("\n\nLet's test our own iterator.\n"); let users = UserCollection::new(); let mut iterator = users.iter(); println!("1nd element: {:?}", iterator.next()); println!("2nd element: {:?}", iterator.next()); println!("3rd element: {:?}", iterator.next()); println!("4th element: {:?}", iterator.next()); print!("\nAll elements in user collection: "); users.iter().for_each(|e| print!("{} ", e)); println!(); } 

Iterators are widely used in the standard library: 1 2 3 Let's test our own iterator. 1nd element: Some("Alice") 2nd element: Some("Bob") 3rd element: Some("Carl") 4th element: None All elements in user collection: Alice Bob Carl