Iter Functions

Iterator creation และ utility functions ใน std::iter module สำหรับสร้างและ manipulate iterators

1. std::iter Creation Functions

Functions สำหรับสร้าง iterators จาก scratch

Iterator Constructors

use std::iter;

fn main() {
    // repeat - infinite iterator of same value
    let fives: Vec<_> = iter::repeat(5).take(5).collect();
    println!("repeat: {:?}", fives);

    // repeat_with - infinite from closure (lazy)
    let mut counter = 0;
    let nums: Vec<_> = iter::repeat_with(|| {
        counter += 1;
        counter
    }).take(5).collect();
    println!("repeat_with: {:?}", nums);

    // once - single element
    let single: Vec<_> = iter::once(42).collect();
    println!("once: {:?}", single);

    // once_with - single from closure (lazy)
    let computed: Vec<_> = iter::once_with(|| {
        println!("Computing...");
        42
    }).collect();
    println!("once_with: {:?}", computed);

    // empty - no elements
    let empty: Vec<i32> = iter::empty().collect();
    println!("empty: {:?}", empty);

    // from_fn - from closure that returns Option
    let mut count = 0;
    let limited: Vec<_> = iter::from_fn(|| {
        if count < 5 {
            count += 1;
            Some(count)
        } else {
            None
        }
    }).collect();
    println!("from_fn: {:?}", limited);
}