I don't understand what your concern is - this only took me about a minute to write and it looks completely safe and efficient.
https://play.rust-lang.org/?gist=674f4b88876614f603fd70368cb...
https://play.rust-lang.org/?gist=674f4b88876614f603fd70368cb...
If I understand correctly that's overly restrictive though. You're limiting the lifetime of list elements to the lifetime of the spine of the list.
What I want is this:
enum List<T> {
Nil,
Cons(T, Box<List<T>>)
}
struct IntoIter<T>(List<T>);
impl<T> IntoIterator for List<T> {
type Item = T;
type IntoIter = IntoIter<T>;
fn into_iter(self) -> Self::IntoIter {
IntoIter(self)
}
}
impl<T> Iterator for IntoIter<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
match std::mem::replace(&mut self.0, List::Nil) {
List::Nil => None,
List::Cons(x, l) => {
std::mem::replace(&mut self.0, *l);
Some(x)
}
}
}
}
Also, in general I may be working with a data type for which I don't have a value I can conjure out of thin air (like `Nil`). What then?