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use std::hash::Hash;
mod private {
use std::collections::HashMap;
use std::hash::Hash;
use std::fmt;
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct DuplicatesBy<I: Iterator, Key, F> {
pub(crate) iter: I,
pub(crate) meta: Meta<Key, F>,
}
impl<I, V, F> fmt::Debug for DuplicatesBy<I, V, F>
where
I: Iterator + fmt::Debug,
V: fmt::Debug + Hash + Eq,
{
debug_fmt_fields!(DuplicatesBy, iter, meta.used);
}
impl<I: Iterator, Key: Eq + Hash, F> DuplicatesBy<I, Key, F> {
pub(crate) fn new(iter: I, key_method: F) -> Self {
DuplicatesBy {
iter,
meta: Meta {
used: HashMap::new(),
pending: 0,
key_method,
},
}
}
}
#[derive(Clone)]
pub struct Meta<Key, F> {
used: HashMap<Key, bool>,
pending: usize,
key_method: F,
}
impl<Key, F> Meta<Key, F>
where
Key: Eq + Hash,
{
/// Takes an item and returns it back to the caller if it's the second time we see it.
/// Otherwise the item is consumed and None is returned
#[inline(always)]
fn filter<I>(&mut self, item: I) -> Option<I>
where
F: KeyMethod<Key, I>,
{
let kv = self.key_method.make(item);
match self.used.get_mut(kv.key_ref()) {
None => {
self.used.insert(kv.key(), false);
self.pending += 1;
None
}
Some(true) => None,
Some(produced) => {
*produced = true;
self.pending -= 1;
Some(kv.value())
}
}
}
}
impl<I, Key, F> Iterator for DuplicatesBy<I, Key, F>
where
I: Iterator,
Key: Eq + Hash,
F: KeyMethod<Key, I::Item>,
{
type Item = I::Item;
fn next(&mut self) -> Option<Self::Item> {
let DuplicatesBy { iter, meta } = self;
iter.find_map(|v| meta.filter(v))
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, hi) = self.iter.size_hint();
let hi = hi.map(|hi| {
if hi <= self.meta.pending {
// fewer or equally many iter-remaining elements than pending elements
// => at most, each iter-remaining element is matched
hi
} else {
// fewer pending elements than iter-remaining elements
// => at most:
// * each pending element is matched
// * the other iter-remaining elements come in pairs
self.meta.pending + (hi - self.meta.pending) / 2
}
});
// The lower bound is always 0 since we might only get unique items from now on
(0, hi)
}
}
impl<I, Key, F> DoubleEndedIterator for DuplicatesBy<I, Key, F>
where
I: DoubleEndedIterator,
Key: Eq + Hash,
F: KeyMethod<Key, I::Item>,
{
fn next_back(&mut self) -> Option<Self::Item> {
let DuplicatesBy { iter, meta } = self;
iter.rev().find_map(|v| meta.filter(v))
}
}
/// A keying method for use with `DuplicatesBy`
pub trait KeyMethod<K, V> {
type Container: KeyXorValue<K, V>;
fn make(&mut self, value: V) -> Self::Container;
}
/// Apply the identity function to elements before checking them for equality.
#[derive(Debug)]
pub struct ById;
impl<V> KeyMethod<V, V> for ById {
type Container = JustValue<V>;
fn make(&mut self, v: V) -> Self::Container {
JustValue(v)
}
}
/// Apply a user-supplied function to elements before checking them for equality.
pub struct ByFn<F>(pub(crate) F);
impl<F> fmt::Debug for ByFn<F> {
debug_fmt_fields!(ByFn,);
}
impl<K, V, F> KeyMethod<K, V> for ByFn<F>
where
F: FnMut(&V) -> K,
{
type Container = KeyValue<K, V>;
fn make(&mut self, v: V) -> Self::Container {
KeyValue((self.0)(&v), v)
}
}
// Implementors of this trait can hold onto a key and a value but only give access to one of them
// at a time. This allows the key and the value to be the same value internally
pub trait KeyXorValue<K, V> {
fn key_ref(&self) -> &K;
fn key(self) -> K;
fn value(self) -> V;
}
#[derive(Debug)]
pub struct KeyValue<K, V>(K, V);
impl<K, V> KeyXorValue<K, V> for KeyValue<K, V> {
fn key_ref(&self) -> &K {
&self.0
}
fn key(self) -> K {
self.0
}
fn value(self) -> V {
self.1
}
}
#[derive(Debug)]
pub struct JustValue<V>(V);
impl<V> KeyXorValue<V, V> for JustValue<V> {
fn key_ref(&self) -> &V {
&self.0
}
fn key(self) -> V {
self.0
}
fn value(self) -> V {
self.0
}
}
}
/// An iterator adapter to filter for duplicate elements.
///
/// See [`.duplicates_by()`](crate::Itertools::duplicates_by) for more information.
pub type DuplicatesBy<I, V, F> = private::DuplicatesBy<I, V, private::ByFn<F>>;
/// Create a new `DuplicatesBy` iterator.
pub fn duplicates_by<I, Key, F>(iter: I, f: F) -> DuplicatesBy<I, Key, F>
where
Key: Eq + Hash,
F: FnMut(&I::Item) -> Key,
I: Iterator,
{
DuplicatesBy::new(iter, private::ByFn(f))
}
/// An iterator adapter to filter out duplicate elements.
///
/// See [`.duplicates()`](crate::Itertools::duplicates) for more information.
pub type Duplicates<I> = private::DuplicatesBy<I, <I as Iterator>::Item, private::ById>;
/// Create a new `Duplicates` iterator.
pub fn duplicates<I>(iter: I) -> Duplicates<I>
where
I: Iterator,
I::Item: Eq + Hash,
{
Duplicates::new(iter, private::ById)
}
|
