IntoIterator

The Iterator trait tells you how to iterate once you have created an iterator. The related trait IntoIterator defines how to create an iterator for a type. It is used automatically by the for loop.

struct Grid {
    x_coords: Vec<u32>,
    y_coords: Vec<u32>,
}
impl IntoIterator for Grid {
    type Item = (u32, u32);
    type IntoIter = GridIter;
    fn into_iter(self) -> GridIter {
        GridIter { grid: self, i: 0, j: 0 }
    }
}
struct GridIter {
    grid: Grid,
    i: usize,
    j: usize,
}
impl Iterator for GridIter {
    type Item = (u32, u32);
    fn next(&mut self) -> Option<(u32, u32)> {
        if self.i >= self.grid.x_coords.len() {
            self.i = 0;
            self.j += 1;
            if self.j >= self.grid.y_coords.len() {
                return None;
            }
        }
        let res = Some((self.grid.x_coords[self.i], self.grid.y_coords[self.j]));
        self.i += 1;
        res
    }
}
fn main() {
    let grid = Grid { x_coords: vec![3, 5, 7, 9], y_coords: vec![10, 20, 30, 40] };
    for (x, y) in grid {
        println!("point = {x}, {y}");
    }
}

This slide should take about 5 minutes.

Click through to the docs for IntoIterator. Every implementation of IntoIterator must declare two types:

• Item: the type to iterate over, such as i8,
• “IntoIter”：“into_iter”方法返回的“Iterator”类型。

Note that IntoIter and Item are linked: the iterator must have the same Item type, which means that it returns Option<Item>

此示例对 x 坐标和 y 坐标的所有组合进行了迭代。

请尝试在 main 中对网格进行两次迭代。为什么会失败？请注意，IntoIterator::into_iter 获得了 self 的所有权。

如要解决此问题，请为 &Grid 实现 IntoIterator，并在 GridIter 中存储对 Grid 的引用。

对于标准库类型，可能会出现同样的问题：for e in some_vector 将获得 some_vector 的所有权，并迭代该矢量中的自有元素。请改用 for e in &some_vector 来迭代 some_vector 的元素的引用。