Rust 我怎样才能把一系列的数字相加呢

我想写一个函数，将数字从零到n求和(理想情况下，这对所有数字都是通用的，但我会接受i32).

mod squares {

    pub fn sum_from_zero( n: i32) -> i32 {
        [0 .. n].fold(0, |a, b| a + b)
    }
}

#[test]
fn test_sum_from_zero() {
    assert_eq!(15, squares::sum_from_zero(5));
}

我发现以下编译器错误:

src/lib.rs:5:18: 5:22 error: no method named `fold` found for type `[std::ops::Range<i32>; 1]` in the current scope
src/lib.rs:5         [0 .. n].fold(0, |a, b| a + b)
                              ^~~~
src/lib.rs:5:18: 5:22 note: the method `fold` exists but the following trait bounds were not satisfied: `[std::ops::Range<i32>; 1] : std::iter::Iterator`, `[std::ops::Range<i32>] : std::iter::Iterator`

我也试过sum()次:

mod squares {

    pub fn sum_from_zero( n: i32) -> i32 {
        [0 .. n].sum()
    }
}

#[test]
fn test_sum_from_zero() {
    assert_eq!(15, squares::sum_from_zero(5));
}

并出现以下编译器错误:

src/lib.rs:5:18: 5:21 error: no method named `sum` found for type `[std::ops::Range<i32>; 1]` in the current scope
src/lib.rs:5         [0 .. n].sum()
                              ^~~
src/lib.rs:5:18: 5:21 note: the method `sum` exists but the following trait bounds were not satisfied: `[std::ops::Range<i32>; 1] : std::iter::Iterator`, `[std::ops::Range<i32>] : std::iter::Iterator`
src/lib.rs:5:18: 5:21 error: no method named `sum` found for type `[std::ops::Range<i32>; 1]` in the current scope
src/lib.rs:5         [0 .. n].sum()
                              ^~~
src/lib.rs:5:18: 5:21 note: the method `sum` exists but the following trait bounds were not satisfied: `[std::ops::Range<i32>; 1] : std::iter::Iterator`, `[std::ops::Range<i32>] : std::iter::Iterator`

我必须声明明确的界限/特征吗？