Move entity into a separate crate (#297)

lib/entity/src/set.rs

@@ -0,0 +1,143 @@
+//! Densely numbered entity references as set keys.
+
+use {EntityRef, Keys};
+use std::marker::PhantomData;
+use std::vec::Vec;
+
+/// A set of `K` for densely indexed entity references.
+///
+/// The `EntitySet` data structure uses the dense index space to implement a set with a bitvector.
+/// Like `EntityMap`, an `EntitySet` is used to associate secondary information with entities.
+#[derive(Debug, Clone)]
+pub struct EntitySet<K>
+where
+    K: EntityRef,
+{
+    elems: Vec<u8>,
+    len: usize,
+    unused: PhantomData<K>,
+}
+
+/// Shared `EntitySet` implementation for all value types.
+impl<K> EntitySet<K>
+where
+    K: EntityRef,
+{
+    /// Create a new empty set.
+    pub fn new() -> Self {
+        Self {
+            elems: Vec::new(),
+            len: 0,
+            unused: PhantomData,
+        }
+    }
+
+    /// Get the element at `k` if it exists.
+    pub fn contains(&self, k: K) -> bool {
+        let index = k.index();
+        if index < self.len {
+            (self.elems[index / 8] & (1 << (index % 8))) != 0
+        } else {
+            false
+        }
+    }
+
+    /// Is this set completely empty?
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
+    /// Remove all entries from this set.
+    pub fn clear(&mut self) {
+        self.len = 0;
+        self.elems.clear()
+    }
+
+    /// Iterate over all the keys in this set.
+    pub fn keys(&self) -> Keys<K> {
+        Keys::new(self.len)
+    }
+
+    /// Resize the set to have `n` entries by adding default entries as needed.
+    pub fn resize(&mut self, n: usize) {
+        self.elems.resize((n + 7) / 8, 0);
+        self.len = n
+    }
+
+    /// Insert the element at `k`.
+    pub fn insert(&mut self, k: K) -> bool {
+        let index = k.index();
+        if index >= self.len {
+            self.resize(index + 1)
+        }
+        let result = !self.contains(k);
+        self.elems[index / 8] |= 1 << (index % 8);
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::u32;
+
+    // `EntityRef` impl for testing.
+    #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+    struct E(u32);
+
+    impl EntityRef for E {
+        fn new(i: usize) -> Self {
+            E(i as u32)
+        }
+        fn index(self) -> usize {
+            self.0 as usize
+        }
+    }
+
+    #[test]
+    fn basic() {
+        let r0 = E(0);
+        let r1 = E(1);
+        let r2 = E(2);
+        let mut m = EntitySet::new();
+
+        let v: Vec<E> = m.keys().collect();
+        assert_eq!(v, []);
+        assert!(m.is_empty());
+
+        m.insert(r2);
+        m.insert(r1);
+
+        assert!(!m.contains(r0));
+        assert!(m.contains(r1));
+        assert!(m.contains(r2));
+        assert!(!m.contains(E(3)));
+        assert!(!m.is_empty());
+
+        let v: Vec<E> = m.keys().collect();
+        assert_eq!(v, [r0, r1, r2]);
+
+        m.resize(20);
+        assert!(!m.contains(E(3)));
+        assert!(!m.contains(E(4)));
+        assert!(!m.contains(E(8)));
+        assert!(!m.contains(E(15)));
+        assert!(!m.contains(E(19)));
+
+        m.insert(E(8));
+        m.insert(E(15));
+        assert!(!m.contains(E(3)));
+        assert!(!m.contains(E(4)));
+        assert!(m.contains(E(8)));
+        assert!(!m.contains(E(9)));
+        assert!(!m.contains(E(14)));
+        assert!(m.contains(E(15)));
+        assert!(!m.contains(E(16)));
+        assert!(!m.contains(E(19)));
+        assert!(!m.contains(E(20)));
+        assert!(!m.contains(E(u32::MAX)));
+
+        m.clear();
+        assert!(m.is_empty());
+    }
+}