Im trying to understand how to use ranges with iterators. If I declare a range and use it with an iterator, is it possible to re-use that range with another iterator? For example this does not compile:
fn main() {
let smallr = 0..10;
for i in smallr {
println!("value is {}", i);
}
//let smallr = 0..15; re-defining smallr will work!
let sum = smallr.fold(0, |sum, x| sum + x);
println!("{}", sum);
}
The range type Range does not implement Copy. Therefor using a range in a for loop will consume it. If you want to create a copy of a range, you can use .clone():
for i in smallr.clone() {
println!("value is {}", i);
}
Note that this might cause confusing behavior when used on a mutable range (which afaik is the reason why Range does not implement Copy). A range is also an iterator at the same time. If you only partially consume the iterator and then clone it, You get a clone of the partially consumed iterator.
As an example of the pitfall:
fn main() {
let mut smallr = 0..10;
println!("first: {:?}", smallr.next());
for i in smallr.clone() {
println!("value is {}", i);
}
}
prints
first: Some(0)
value is 1
value is 2
value is 3
value is 4
value is 5
value is 6
value is 7
value is 8
value is 9
which shows that the first value of the range is not part of the cloned iterator.
