--- a/rust/hwphysics/src/common.rs	Thu Jul 25 21:59:20 2019 +0300
+++ b/rust/hwphysics/src/common.rs	Thu Jul 25 22:31:24 2019 +0300
@@ -1,10 +1,40 @@
-pub type GearId = std::num::NonZeroU16;
+use std::{collections::BinaryHeap, num::NonZeroU16};
+
+pub type GearId = NonZeroU16;
 pub trait GearData {}
 
 pub trait GearDataProcessor<T: GearData> {
     fn add(&mut self, gear_id: GearId, gear_data: T);
+    fn remove(&mut self, gear_id: GearId);
 }
 
 pub trait GearDataAggregator<T: GearData> {
     fn find_processor(&mut self) -> &mut GearDataProcessor<T>;
 }
+
+pub struct GearAllocator {
+    max_id: u16,
+    free_ids: BinaryHeap<GearId>,
+}
+
+impl GearAllocator {
+    pub fn new() -> Self {
+        Self {
+            max_id: 0,
+            free_ids: BinaryHeap::with_capacity(1024),
+        }
+    }
+
+    pub fn alloc(&mut self) -> Option<GearId> {
+        self.free_ids.pop().or_else(|| {
+            self.max_id.checked_add(1).and_then(|new_max_id| {
+                self.max_id = new_max_id;
+                NonZeroU16::new(new_max_id)
+            })
+        })
+    }
+
+    pub fn free(&mut self, gear_id: GearId) {
+        self.free_ids.push(gear_id)
+    }
+}