Move entity into a separate crate (#297)

lib/entity/src/iter.rs

@@ -0,0 +1,109 @@
+//! A double-ended iterator over entity references and entities.
+
+use EntityRef;
+use std::marker::PhantomData;
+use std::slice;
+
+/// Iterate over all keys in order.
+pub struct Iter<'a, K: EntityRef, V>
+where
+    V: 'a,
+{
+    pos: usize,
+    iter: slice::Iter<'a, V>,
+    unused: PhantomData<K>,
+}
+
+impl<'a, K: EntityRef, V> Iter<'a, K, V> {
+    /// Create an `Iter` iterator that visits the `PrimaryMap` keys and values
+    /// of `iter`.
+    pub fn new(key: K, iter: slice::Iter<'a, V>) -> Self {
+        Self {
+            pos: key.index(),
+            iter,
+            unused: PhantomData,
+        }
+    }
+}
+
+impl<'a, K: EntityRef, V> Iterator for Iter<'a, K, V> {
+    type Item = (K, &'a V);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(next) = self.iter.next() {
+            let pos = self.pos;
+            self.pos += 1;
+            Some((K::new(pos), next))
+        } else {
+            None
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl<'a, K: EntityRef, V> DoubleEndedIterator for Iter<'a, K, V> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if let Some(next_back) = self.iter.next_back() {
+            Some((K::new(self.pos), next_back))
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a, K: EntityRef, V> ExactSizeIterator for Iter<'a, K, V> {}
+
+/// Iterate over all keys in order.
+pub struct IterMut<'a, K: EntityRef, V>
+where
+    V: 'a,
+{
+    pos: usize,
+    iter: slice::IterMut<'a, V>,
+    unused: PhantomData<K>,
+}
+
+impl<'a, K: EntityRef, V> IterMut<'a, K, V> {
+    /// Create an `IterMut` iterator that visits the `PrimaryMap` keys and values
+    /// of `iter`.
+    pub fn new(key: K, iter: slice::IterMut<'a, V>) -> Self {
+        Self {
+            pos: key.index(),
+            iter,
+            unused: PhantomData,
+        }
+    }
+}
+
+impl<'a, K: EntityRef, V> Iterator for IterMut<'a, K, V> {
+    type Item = (K, &'a mut V);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(next) = self.iter.next() {
+            let pos = self.pos;
+            self.pos += 1;
+            Some((K::new(pos), next))
+        } else {
+            None
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl<'a, K: EntityRef, V> DoubleEndedIterator for IterMut<'a, K, V> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if let Some(next_back) = self.iter.next_back() {
+            Some((K::new(self.pos), next_back))
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a, K: EntityRef, V> ExactSizeIterator for IterMut<'a, K, V> {}