Rust 1.28+
Iterator::step_by
is now stable:
fn main() {
for i in (0..100).step_by(2) {
println!("{}", i);
}
}
Rust 1.1+
您总可以老式地编写它:
fn main() {
let mut i = 0;
while i < 100 {
println!("i: {}", i);
i += 2;
}
}
然后可以抽象出:
use std::ops::Add;
fn step_by<T, F>(start: T, end_exclusive: T, step: T, mut body: F)
where
T: Add<Output = T> + PartialOrd + Copy,
F: FnMut(T),
{
let mut i = start;
while i < end_exclusive {
body(i);
i = i + step;
}
}
fn main() {
step_by(0, 100, 2, |i| {
println!("i: {}", i);
})
}
有趣的历史注解,我相信最初所有的循环都是使用类似这样的闭包完成的,在迭代器变得极为普遍之前。
然后你可以将它转换成一个迭代器:
use std::ops::Add;
struct StepBy<T> {
start: T,
end_exclusive: T,
step: T,
}
impl<T> StepBy<T> {
fn new(start: T, end_exclusive: T, step: T) -> Self {
Self {
start,
end_exclusive,
step,
}
}
}
impl<T> Iterator for StepBy<T>
where
T: Add<Output = T> + PartialOrd + Copy,
{
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
if self.start < self.end_exclusive {
let v = self.start;
self.start = self.start + self.step;
Some(v)
} else {
None
}
}
}
fn main() {
for i in StepBy::new(0, 100, 2) {
println!("i: {}", i);
}
}
参见: