13.3 Creating Custom Iterators

Although the standard library covers most common scenarios, you may occasionally need a custom iterator for specialized data structures. To create your own iterator:

  1. Define a struct to keep track of iteration state.
  2. Implement the Iterator trait, writing a next() method that yields items until no more remain.

13.3.1 A Simple Range-Like Iterator

#![allow(unused)]
fn main() {
struct MyRange {
    current: u32,
    end: u32,
}

impl MyRange {
    fn new(start: u32, end: u32) -> Self {
        MyRange { current: start, end }
    }
}
}

13.3.2 Implementing the Iterator Trait

#![allow(unused)]
fn main() {
impl Iterator for MyRange {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        if self.current < self.end {
            let result = self.current;
            self.current += 1;
            Some(result)
        } else {
            None
        }
    }
}
}

13.3.3 Using a Custom Iterator

struct MyRange {
    current: u32,
    end: u32,
}
impl MyRange {
    fn new(start: u32, end: u32) -> Self {
        MyRange { current: start, end }
    }
}
impl Iterator for MyRange {
    type Item = u32;
    fn next(&mut self) -> Option<Self::Item> {
        if self.current < self.end {
            let result = self.current;
            self.current += 1;
            Some(result)
        } else {
            None
        }
    }
}
fn main() {
    let range = MyRange::new(10, 15);
    for number in range {
        print!("{} ", number);
    }
    // 10 11 12 13 14
}

13.3.4 A Fibonacci Iterator

#![allow(unused)]
fn main() {
struct Fibonacci {
    current: u32,
    next: u32,
    max: u32,
}

impl Fibonacci {
    fn new(max: u32) -> Self {
        Fibonacci {
            current: 0,
            next: 1,
            max,
        }
    }
}

impl Iterator for Fibonacci {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        if self.current > self.max {
            None
        } else {
            let new_next = self.current + self.next;
            let result = self.current;
            self.current = self.next;
            self.next = new_next;
            Some(result)
        }
    }
}
}