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use std::iter::Peekable;
use std::cell::Cell;
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum Position {
First,
Middle,
Last,
Only,
}
impl Position {
pub fn is_first(self) -> bool {
self == Position::First || self == Position::Only
}
pub fn is_last(self) -> bool {
self == Position::Last || self == Position::Only
}
pub fn is_only(self) -> bool {
self == Position::Only
}
}
pub struct PositionIterator<T> where T: Iterator {
iter: Peekable<T>,
did_iter: Cell<bool>,
}
impl<T> Iterator for PositionIterator<T> where T: Iterator {
type Item = (Position, T::Item);
fn next(&mut self) -> Option<Self::Item> {
let is_first = self.did_iter.get();
self.did_iter.set(true);
let next = match self.iter.next() {
Some(item) => item,
None => return None,
};
if is_first {
match self.iter.peek() {
Some(_) => Some((Position::Middle, next)),
None => Some((Position::Last, next)),
}
} else {
match self.iter.peek() {
Some(_) => Some((Position::First, next)),
None => Some((Position::Only, next)),
}
}
}
}
pub trait WithPosition where {
type Iterator: Iterator;
fn with_position(self) -> PositionIterator<Self::Iterator>;
}
impl<T> WithPosition for T where T: Iterator {
type Iterator = T;
fn with_position(self) -> PositionIterator<T> {
PositionIterator { iter: self.peekable(), did_iter: Cell::new(false) }
}
}
#[cfg(test)]
mod tests {
use super::{WithPosition, Position};
#[test]
fn it_marks_first_middle_and_last_position() {
let result: Vec<_> = vec![1,2,3,4].into_iter().with_position().collect();
assert_eq!(result[0], (Position::First, 1));
assert_eq!(result[1], (Position::Middle, 2));
assert_eq!(result[2], (Position::Middle, 3));
assert_eq!(result[3], (Position::Last, 4));
}
#[test]
fn it_marks_first_and_last_position() {
let result: Vec<_> = vec![1,4].into_iter().with_position().collect();
assert_eq!(result[0], (Position::First, 1));
assert_eq!(result[1], (Position::Last, 4));
}
#[test]
fn it_marks_only_position() {
let result: Vec<_> = vec![2].into_iter().with_position().collect();
assert_eq!(result[0], (Position::Only, 2));
}
#[test]
fn it_has_boolean_methods_on_position() {
assert_eq!(Position::First.is_first(), true);
assert_eq!(Position::Middle.is_first(), false);
assert_eq!(Position::Last.is_first(), false);
assert_eq!(Position::Only.is_first(), true);
assert_eq!(Position::First.is_last(), false);
assert_eq!(Position::Middle.is_last(), false);
assert_eq!(Position::Last.is_last(), true);
assert_eq!(Position::Only.is_last(), true);
assert_eq!(Position::First.is_only(), false);
assert_eq!(Position::Middle.is_only(), false);
assert_eq!(Position::Last.is_only(), false);
assert_eq!(Position::Only.is_only(), true);
}
}