在 Rust 中动态创建任一方向的范围 [英] Dynamically create a range in either direction in Rust
问题描述
我正在学习 Rust，最近进行了一项练习，我必须遍历可能朝任一方向发展的数字.我尝试了以下方法，结果出乎意料.
I am learning Rust and recently went through an exercise where I had to iterate through numbers that could go in either direction. I tried the below with unexpected results.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
struct Point {
x: i32,
y: i32
}
fn test() {
let p1 = Point { x: 1, y: 8 };
let p2 = Point { x: 3, y: 6 };
let all_x = p1.x..=p2.x;
println!("all_x: {:?}", all_x.clone().collect::<Vec<i32>>());
let all_y = p1.y..=p2.y;
println!("all_y: {:?}", all_y.clone().collect::<Vec<i32>>());
let points: Vec<Point> = all_x.zip(all_y).map(|(x, y)| Point { x, y }).collect();
println!("points: {:?}", points);
}
输出是
all_x: [1, 2, 3]
all_y: []
points: []
经过一番谷歌搜索，我找到了一个 解释 和一些 旧 answers 基本上相当于使用 (a..b).rev()根据需要.
After some googling I found an explanation and some old answers which basically amount to use (a..b).rev() as needed.
我的问题是，我如何以动态方式执行此操作?如果我像这样使用 if...else
My question is, how do I do this in a dynamic way? If I use an if...else like so
let all_x = if p1.x < p2.x { (p1.x..=p2.x) } else { (p2.x..=p1.x).rev() };
我收到类型错误，因为 else 与 if
I get a type error because the else is different than the if
|
58 | let all_x = if p1.x < p2.x { (p1.x..=p2.x) }
| - ------------- expected because of this
| _________________|
| |
59 | | else { (p2.x..=p1.x).rev() };
| |____________^^^^^^^^^^^^^^^^^^^_- `if` and `else` have incompatible types
| |
| expected struct `RangeInclusive`, found struct `Rev`
|
= note: expected type `RangeInclusive<_>`
found struct `Rev<RangeInclusive<_>>`
在尝试了 let all_x: dyn Range、let all_x: dyn Iterator 等一系列不同的变体之后，我设法做到这一点的唯一方法是将它们转换为集合，然后返回到迭代器.
After trying a bunch of different variations on let all_x: dyn Range<Item = i32>, let all_x: dyn Iterator<Item = i32>, etc, the only way I have managed to do this is by turning them into collections and then back to iterators.
let all_x: Vec<i32>;
if p1.x < p2.x { all_x = (p1.x..=p2.x).collect(); }
else { all_x = (p2.x..=p1.x).rev().collect(); }
let all_x = all_x.into_iter();
println!("all_x: {:?}", all_x.clone().collect::<Vec<i32>>());
let all_y: Vec<i32>;
if p1.y < p2.y { all_y = (p1.y..=p2.y).collect(); }
else { all_y = (p2.y..=p1.y).rev().collect(); }
let all_y = all_y.into_iter();
println!("all_y: {:?}", all_y.clone().collect::<Vec<i32>>());
提供期望的结果
all_x: [1, 2, 3]
all_y: [8, 7, 6]
points: [Point { x: 1, y: 8 }, Point { x: 2, y: 7 }, Point { x: 3, y: 6 }]
但有点重复，不优雅，我假设在大量使用时效率不高.有没有更好的方法来处理这种情况?
but is a bit repetitive, inelegant and I'm assuming not very efficient at large numbers. Is there a better way to handle this situation?
注意:很抱歉包含 Point 结构.我无法让我的示例与 x1、x2 等一起使用.对于不同的帖子可能会有不同的问题，哈哈.
NOTE: Sorry for including the Point struct. I could not get my example to work with x1, x2, etc. Probably a different question for a different post lol.
推荐答案
你可以动态调度它.将它们包装成 Box 并返回一个动态对象，在本例中为 Iterator.例如:
You can dynamically dispatch it. Wrapping them into a Box and returning a dynamic object, an Iterator in this case. For example:
fn maybe_reverse_range(init: usize, end: usize, reverse: bool) -> Box<dyn Iterator<Item=usize>> {
if reverse {
Box::new((init..end).rev())
} else {
Box::new((init..end))
}
}
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