link#

Summary#

• traits의 Iterator 기능 중 fold와 reduce를 알아보자 & Iterator 활용

trait.Iterator#

• https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html

array.map#

• https://doc.rust-lang.org/stable/std/primitive.array.html#method.map

fold & reduce 활용#

• https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html#method.fold

• https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html#method.reduce

• 둘다 타입 변환 가능

  • fold는 리턴값이 직접 값이 나온다
    • fold - Uses *x as u32 to cast each &i32 to u32 before adding
    • 접기 - *x를 u32로 사용하여 각 &i32를 u32로 캐스팅한 후 추가합니다
  • reduce는 Option<T>가 나옴
    • reduce - First maps i32 to u32, then reduces (returns Option)
    • 축소 - 먼저 i32를 u32로 매핑한 다음 축소((옵션)Option 반환)합니다

⏺ Fixed. The key difference between fold and reduce for type conversion:

Summary of changes:

• Line 82: fold - Uses *x as u32 to cast each &i32 to u32 before adding

• Line 86: reduce - First maps i32 to u32, then reduces (returns Option)

• Rust code

let my_arr: [i32, 4] = [10, 20, 30, 40];

// Fold : Reduce to single value (i32 -> u32 conversion)
let my_fold_arr: u32 = my_arr
                        .iter()
                        .fold(0u32, |acc, x| acc + *x as u32);

println!("arr fold (i32->u32) :{my_fold_arr}");

// Reduce : Alternative without initial value (returns Option)
let my_reduce_arr: Option<u32> = my_arr
                                    .iter()
                                    .map(|x| *x as u32)
                                    .reduce(|acc, x| acc + x);

println!("arr reduce (i32->u32) :{my_reduce_arr:?}");

• result

arr fold (i32->u32) :100
arr reduce (i32->u32) :Some(100)

Iterator추가#

trait MySumExt: Sized {
    fn my_sum(self) -> i32;
    fn my_product(self) -> i32;
}

// impl<T: Iterator<Item = i32>> MySumExt for T
impl<T> MySumExt for T
where
    T: Iterator<Item = i32>,
{
    fn my_sum(self) -> i32 {
        let mut total = 0;
        for num in self {
            total += num;
        }
        total
    }

    fn my_product(self) -> i32 {
        let mut my_total = 1;
        for num in self {
            my_total *= num;
        }
        my_total
    }
}

fn main() {
    let my_arr = [10, 20, 30, 40];

    // my_sum()  custom method
    let sum_arr: i32 = my_arr.iter().copied().my_sum();

    // my_fn  "my_product"
    let my_product_arr = my_arr.iter().copied().my_product();
    println!("arr product :{my_product_arr:?}");