1 files changed, 47 insertions, 0 deletions
diff --git a/ops/src/ageset.rs b/ops/src/ageset.rs
new file mode 100644
index 0000000..c97240f
--- /dev/null
+++ b/ops/src/ageset.rs
@@ -0,0 +1,47 @@
+use std::collections::HashSet;
+use std::hash::Hash;
+
+use blist::BList;
+
+/// So... this is a rather weird thing.
+/// It allows to semi-efficiently check the oldest (earliest insertion)
+/// elements for certain criteria and remove them in the order of insertion
+/// if the criteria is met.
+pub struct AgeSet<T> {
+    fifo: BList<T>,
+    set: HashSet<T>,
+}
+
+impl<T> AgeSet<T>
+    where T: Eq + Hash + Clone
+{
+    pub fn new() -> Self {
+        AgeSet {
+            fifo: BList::new(),
+            set: HashSet::new(),
+        }
+    }
+
+    pub fn contains(&self, t: &T) -> bool {
+        self.set.contains(t)
+    }
+
+    pub fn prune<F>(&mut self, kill: F)
+        where F: Fn(&T) -> bool
+    {
+        while let Some(ref e) = self.fifo.front().map(T::clone) {
+            if kill(&e) {
+                let removed = self.fifo.pop_front().unwrap();
+                self.set.remove(&e);
+                assert!(*e == removed);
+            } else {
+                break;
+            }
+        }
+    }
+
+    pub fn push(&mut self, t: T) {
+        self.fifo.push_back(t.clone());
+        self.set.insert(t);
+    }
+}