iterator.rst

Iterator

目錄

• 一般使用
• zip
  • Example 1
  • Example 2
  • Reverse
  • Example
• Peakable
• for each
• Reference

一般使用

Python :

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> for i in a:
...     print(i)
...
0
1
2
3
4
5
6
7
8
9

Rust :

fn main() {
    let a = 0..10;
    for i in a {
        println!("{}", i);
    }
}

// $ ./tmp
// 0
// 1
// 2
// 3
// 4
// 5
// 6
// 7
// 8
// 9

zip

Example 1

Python :

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list(zip(a, a))
[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6), (7, 7), (8, 8), (9, 9)]

Rust :

fn main() {
    let a: Vec<_> = (0..10).collect();
    let result: Vec<_> = a.iter()
                          .zip(a.iter())
                          .collect();
    println!("{:?}", result);
}

fn main() {
    let result: Vec<_> = (0..10).zip(0..10).collect();
    println!("{:?}", result);
}

// $ ./tmp
// [(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6), (7, 7), (8, 8), (9, 9)]

Example 2

Python :

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> it1 = iter(a)
>>> it2 = iter(a)
>>> next(it2)
0
>>> list(zip(it1, it2))
[(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 6), (6, 7), (7, 8), (8, 9)]

Rust :

fn main() {
    let a: Vec<_> = (0..10).collect();
    let result: Vec<_> = a.iter()
                          .zip(a.iter().skip(1))
                          .collect();
    println!("{:?}", result);
}

// $ ./tmp
// [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 6), (6, 7), (7, 8), (8, 9)]

Reverse

Python :

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list(zip(a, a[::-1]))
[(0, 9), (1, 8), (2, 7), (3, 6), (4, 5), (5, 4), (6, 3), (7, 2), (8, 1), (9, 0)]

Rust :

fn main() {
    let a: Vec<_> = (0..10).collect();
    let result: Vec<_> = a.iter()
                          .zip(a.iter().rev())
                          .collect();
    println!("{:?}", result);
}

// $ ./tmp
// [(0, 9), (1, 8), (2, 7), (3, 6), (4, 5), (5, 4), (6, 3), (7, 2), (8, 1), (9, 0)]

Example

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list(zip(*[iter(a)]*2))
[(0, 1), (2, 3), (4, 5), (6, 7), (8, 9)]

Peakable

Rust :

fn main() {
    let s = "這是測試";
    let mut it = s.chars().peekable();

    while !it.is_empty() {
        let (i, j) = (it.next(), it.peek());
        println!("{} {}", i.unwrap(), j.unwrap_or(&' '));
    }
}

Output :

這 是
是 測
測 試
試

for each

實做：

#[inline]
#[stable(feature = "iterator_for_each", since = "1.21.0")]
fn for_each<F>(self, mut f: F) where
    Self: Sized, F: FnMut(Self::Item),
{
    self.fold((), move |(), item| f(item));
}

for_each 是 idiomatic 的 for loop， 但是不允許 break 和 continue ， 在某些情況下 for_each 可能會比 for loop 快。

• PR #42782 - Add Iterator::for_each

Reference

• Rust - Module std::iter