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#[derive(Debug, Clone)]
pub struct AtLeastIter<I, T, E, Factory>
where
I: Iterator<Item = Result<T, E>>,
Factory: Fn(usize) -> E,
{
iter: I,
min_count: usize,
counter: usize,
enumeration_counter: usize,
factory: Factory,
}
impl<I, T, E, Factory> AtLeastIter<I, T, E, Factory>
where
I: Iterator<Item = Result<T, E>>,
Factory: Fn(usize) -> E,
{
pub(crate) fn new(
iter: I,
min_count: usize,
factory: Factory,
) -> AtLeastIter<I, T, E, Factory> {
AtLeastIter {
iter,
min_count,
counter: 0,
enumeration_counter: 0,
factory,
}
}
}
impl<I, T, E, Factory> Iterator for AtLeastIter<I, T, E, Factory>
where
I: Iterator<Item = Result<T, E>>,
Factory: Fn(usize) -> E,
{
type Item = Result<T, E>;
fn next(&mut self) -> Option<Self::Item> {
let item = match self.iter.next() {
Some(Ok(val)) => {
self.counter += 1;
Some(Ok(val))
}
None => match self.counter >= self.min_count {
true => None,
false => {
self.counter = self.min_count;
Some(Err((self.factory)(self.enumeration_counter)))
}
},
other => other,
};
self.enumeration_counter += 1;
item
}
}
pub trait AtLeast<T, E, Factory>: Iterator<Item = Result<T, E>> + Sized
where
Factory: Fn(usize) -> E,
{
/// Fails a validation iterator if it does not contain `n` or more elements.
///
/// `at_least(n, factory)` yields `Ok(element)` values until the iteration ends. If the
/// number of values in the iteration is less than `n`, a new element is
/// added to the end of the iteration with the value returned from calling `factory`
/// on the length of the iterator.
///
/// The `at_least` adapter cannot handle short-circuiting of iterators, so
/// iterations such as `(0..10).validate().at_least(100).take(5)` will not
/// fail.
///
/// Elements already wrapped in `Result::Err` will not be
/// counted towards reaching the `n` elements lower bound.
/// The length provided to `factory` includes elements wrapped in `Result::Err`.
///
/// # Examples
///
/// Basic usage:
/// ```
/// # use validiter::AtLeast;
/// # let a = [1, 2, 3];
/// # #[derive(Debug, PartialEq)]
/// struct NotEnough(usize);
/// let mut iter = a.iter().map(|v| Ok(v)).at_least(4, |i| NotEnough(i));
///
/// assert_eq!(iter.next(), Some(Ok(&1)));
/// assert_eq!(iter.next(), Some(Ok(&2)));
/// assert_eq!(iter.next(), Some(Ok(&3)));
/// assert_eq!(iter.next(), Some(Err(NotEnough(3))));
/// assert_eq!(iter.next(), None);
/// ```
///
/// `at_least` could be used to ensure that a vector created from an iterator
/// has a value in some index:
/// ```
/// use validiter::AtLeast;
/// let iter = 0..=2; // iteration is too short, no 4th element!
///
/// let collection: Result<Vec<_>, _> = iter
/// .map(|v| Ok(v))
/// .at_least(4, |_| Err::<i32, ()>(()))
/// .collect();
///
/// match collection {
/// Ok(vec) => {
/// let val = vec[3]; // doesn't crash, because the collection failed.
/// }
/// Err(_) => {} // handle error
/// };
/// ```
/// `at_least` will not account for errors already in the iteration:
/// ```
/// # use validiter::AtLeast;
/// let mut iter = [Ok(0), Err(404)]
/// .into_iter()
/// .at_least(2, |_| 505);
/// assert_eq!(iter.next(), Some(Ok(0)));
/// assert_eq!(iter.next(), Some(Err(404)));
/// assert_eq!(iter.next(), Some(Err(505)));
/// ```
fn at_least(self, min_count: usize, factory: Factory) -> AtLeastIter<Self, T, E, Factory> {
AtLeastIter::new(self, min_count, factory)
}
}
impl<I, T, E, Factory> AtLeast<T, E, Factory> for I
where
I: Iterator<Item = Result<T, E>>,
Factory: Fn(usize) -> E,
{
}
#[cfg(test)]
mod tests {
use crate::AtLeast;
#[derive(Debug, PartialEq)]
enum TestErr {
NotEnough(usize),
NotOdd(i32),
}
const fn not_enough(index: usize) -> TestErr {
TestErr::NotEnough(index)
}
#[test]
fn test_at_least_on_failure() {
assert_eq!((0..10).map(|i| Ok(i)).at_least(100, not_enough).count(), 11);
(0..10)
.map(|i| Ok(i))
.at_least(100, not_enough)
.enumerate()
.for_each(|(i, res_i)| match res_i {
Ok(_) if i < 10 => {}
Err(TestErr::NotEnough(len)) if i == 10 => {
assert_eq!(len, i)
}
_ => panic!("unexpected value in at least adapter"),
})
}
#[test]
fn test_at_least_on_success() {
assert_eq!((0..10).map(|i| Ok(i)).at_least(5, not_enough).count(), 10);
(0..10)
.map(|i| Ok(i))
.at_least(5, not_enough)
.for_each(|res_i| match res_i {
Ok(_) => {}
_ => panic!("unexpected error in at least adapter"),
})
}
#[test]
fn test_at_least_successful_bounds() {
let tightly_bound_success = (0..10)
.map(|i| Ok(i))
.at_least(10, not_enough)
.collect::<Result<Vec<_>, _>>();
assert!(matches!(tightly_bound_success, Ok(_)));
let empty_success = (0..0)
.map(|i| Ok(i))
.at_least(0, not_enough)
.collect::<Result<Vec<_>, _>>();
assert!(matches!(empty_success, Ok(_)));
}
#[test]
fn test_at_least_unsuccessful_bounds() {
let tightly_bound_failure = (0..10)
.map(|i| Ok(i))
.at_least(11, not_enough)
.collect::<Result<Vec<_>, _>>();
match tightly_bound_failure {
Ok(_) => panic!("collection should fail"),
Err(TestErr::NotEnough(10)) => {}
_ => panic!("bad variant"),
}
let empty_failure = (0..0)
.map(|i| Ok(i))
.at_least(1, not_enough)
.collect::<Result<Vec<_>, _>>();
match empty_failure {
Ok(_) => panic!("collection should fail"),
Err(TestErr::NotEnough(0)) => {}
_ => panic!("bad variant"),
}
}
#[test]
fn test_at_least_all_elements_are_present_and_in_order_on_failure() {
(0..10)
.map(|i| Ok(i))
.at_least(11, not_enough)
.enumerate()
.for_each(|(i, res_i)| match res_i {
Ok(int) if int == i as i32 && i < 10 => {}
Err(TestErr::NotEnough(10)) if i == 10 => {}
_ => panic!("bad iteration after at least adapter failure"),
})
}
#[test]
fn test_at_least_all_elements_are_present_and_in_order_on_success() {
(0..10)
.map(|i| Ok(i))
.at_least(10, not_enough)
.enumerate()
.for_each(|(i, res_i)| match res_i {
Ok(int) if int == i as i32 && i < 10 => {}
_ => panic!("bad iteration after at least adapter success"),
})
}
#[test]
fn test_at_least_does_not_validate_on_short_circuiting_before_last_element() {
(0..10)
.map(|i| Ok(i))
.at_least(100, not_enough)
.take(10)
.for_each(|res_i| match res_i {
Ok(_) => {}
_ => panic!("failed the iteration when last error element was truncated"),
})
}
#[test]
fn test_at_least_validates_on_short_circuiting_after_last_element() {
(0..10)
.map(|i| Ok(i))
.at_least(100, not_enough)
.take(11)
.enumerate()
.for_each(|(i, res_i)| {
match res_i {
Ok(_) if i < 10 => {},
Err(TestErr::NotEnough(10)) if i == 10 => {}
_ => panic!("did not fail the iteration in short circuit when last error element was not truncated")
}
})
}
#[test]
fn test_at_least_counting_iterator_correctly_skips_errors() {
let results = (0..1)
.map(|i| {
if i % 2 == 1 {
return Ok(i);
} else {
Err(TestErr::NotOdd(i))
}
})
.at_least(1, not_enough)
.collect::<Vec<_>>();
assert_eq!(
results,
vec![Err(TestErr::NotOdd(0)), Err(TestErr::NotEnough(1))]
)
}
}