自定义迭代器

struct Fibonacci(u64, u64);

impl Iterator for Fibonacci {
    type Item = u64;
    
    // The method that generates each item
    fn next(&mut self) -> Option<Self::Item> {
        let ret = self.0;
        self.0 = self.1;
        self.1 += ret;
        
        Some(ret) // since `None` is never returned, we have an infinite iterator
    }

    // Implementing the `next()` method suffices since every other iterator
    // method has a default implementation
}

使用示例：

// the iterator method `take()` is an adapter which limits the number of items
// generated by the original iterator
for i in Fibonacci(0, 1).take(10) {
    println!("{}", i);
}