From 0c0563472d70bd6bccdb1b138fec2cc11cdb51ac Mon Sep 17 00:00:00 2001
From: Jason Grlicky <jason@paracosm.us>
Date: Fri, 17 Feb 2017 10:15:18 -0800
Subject: [PATCH] Initial commit

---
 .gitignore |  2 ++
 Cargo.toml |  6 +++++
 src/lib.rs | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.toml
 create mode 100644 src/lib.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a9d37c5
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+target
+Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..13fa09a
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "handlebox"
+version = "0.1.0"
+authors = ["Jason Grlicky <jason@paracosm.us>"]
+
+[dependencies]
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..52e50f7
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,75 @@
+use std::collections::HashMap;
+
+pub type Handle = usize;
+
+/// A HashMap that keeps track of unused keys
+#[derive(Default)]
+pub struct HandleBox<V> {
+    pub hash_map: HashMap<Handle, V>,
+    discarded_handles: Vec<Handle>, // Handles that have been added but later removed
+}
+
+impl<V> HandleBox<V> {
+    pub fn new() -> HandleBox<V> {
+        HandleBox {
+            hash_map: HashMap::new(),
+            discarded_handles: vec![],
+        }
+    }
+
+    fn new_handle(&mut self) -> Handle {
+        self.discarded_handles.pop().unwrap_or(self.hash_map.values().len())
+    }
+
+    pub fn add(&mut self, value: V) -> Handle {
+        let h = self.new_handle();
+        self.hash_map.insert(h, value);
+        h
+    }
+
+    pub fn remove(&mut self, handle: Handle) {
+        let result = self.hash_map.remove(&handle);
+        if result.is_some() {
+            self.discarded_handles.push(handle)
+        }
+    }
+
+    pub fn get(&self, handle: &Handle) -> Option<&V> {
+        self.hash_map.get(handle)
+    }
+
+    pub fn hash_map(&self) -> &HashMap<Handle, V> {
+        &self.hash_map
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_new() {
+        let c = HandleBox::<i32>::new();
+        assert!(c.hash_map().is_empty());
+    }
+
+    #[test]
+    fn test_add_remove() {
+        let mut c = HandleBox::new();
+        let h1 = c.add(888);
+        assert!(!c.hash_map().is_empty());
+        assert_eq!(c.get(&h1).unwrap(), &888);
+
+        let h2 = c.add(999);
+        assert_eq!(c.hash_map().values().len(), 2);
+        assert_eq!(c.get(&h2).unwrap(), &999);
+
+        c.remove(h2);
+        assert_eq!(c.hash_map().values().len(), 1);
+        assert!(c.get(&h2).is_none());
+
+        c.remove(h1);
+        assert!(c.hash_map().is_empty());
+        assert!(c.get(&h1).is_none());
+    }
+}
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