diff --git a/src/lib.rs b/src/lib.rs
index 8d9bd2f..2397095 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,18 +1,20 @@
 use std::cmp::{max, min, Ordering, Reverse};
 use std::collections::BinaryHeap;
-use std::hash::Hash;
-use std::ops::{Index, IndexMut};
 
 use ahash::AHashSet as HashSet;
 #[cfg(feature = "indicatif")]
 use indicatif::ProgressBar;
 use ordered_float::OrderedFloat;
 use rand::rngs::SmallRng;
-use rand::{Rng, SeedableRng};
+use rand::SeedableRng;
 use rayon::iter::{IntoParallelRefMutIterator, ParallelIterator};
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
+mod types;
+pub use types::PointId;
+use types::{Candidate, LayerId, NearestIter, UpperNode, ZeroNode};
+
 /// Parameters for building the `Hnsw`
 pub struct Builder {
     ef_search: Option<usize>,
@@ -475,22 +477,6 @@ impl SearchPool {
     }
 }
 
-impl Layer for [ZeroNode] {
-    fn nearest_iter(&self, pid: PointId) -> NearestIter<'_> {
-        NearestIter {
-            nearest: &self[pid.0 as usize].nearest,
-        }
-    }
-}
-
-impl Layer for [UpperNode] {
-    fn nearest_iter(&self, pid: PointId) -> NearestIter<'_> {
-        NearestIter {
-            nearest: &self[pid.0 as usize].nearest,
-        }
-    }
-}
-
 trait Layer {
     /// Search this layer for nodes near the given `point`
     ///
@@ -687,160 +673,10 @@ impl Default for Search {
     }
 }
 
-#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Default)]
-struct UpperNode {
-    /// The nearest neighbors on this layer
-    ///
-    /// This is always kept in sorted order (near to far).
-    nearest: [PointId; M],
-}
-
-#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug)]
-struct ZeroNode {
-    /// The nearest neighbors on this layer
-    ///
-    /// This is always kept in sorted order (near to far).
-    nearest: [PointId; M * 2],
-}
-
-impl Default for ZeroNode {
-    fn default() -> ZeroNode {
-        ZeroNode {
-            nearest: [PointId::invalid(); M * 2],
-        }
-    }
-}
-
-struct NearestIter<'a> {
-    nearest: &'a [PointId],
-}
-
-impl<'a> Iterator for NearestIter<'a> {
-    type Item = PointId;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        let (&first, rest) = self.nearest.split_first()?;
-        if !first.is_valid() {
-            return None;
-        }
-        self.nearest = rest;
-        Some(first)
-    }
-}
-
-#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
-struct LayerId(usize);
-
-impl LayerId {
-    fn random(ml: f32, rng: &mut SmallRng) -> Self {
-        let layer = rng.gen::<f32>();
-        LayerId((-(layer.ln() * ml)).floor() as usize)
-    }
-
-    fn descend(&self) -> DescendingLayerIter {
-        DescendingLayerIter { next: Some(self.0) }
-    }
-
-    fn is_zero(&self) -> bool {
-        self.0 == 0
-    }
-}
-
-struct DescendingLayerIter {
-    next: Option<usize>,
-}
-
-impl Iterator for DescendingLayerIter {
-    type Item = LayerId;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        Some(LayerId(match self.next? {
-            0 => {
-                self.next = None;
-                0
-            }
-            next => {
-                self.next = Some(next - 1);
-                next
-            }
-        }))
-    }
-}
-
 pub trait Point: Clone + Sync {
     fn distance(&self, other: &Self) -> f32;
 }
 
-#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
-struct Candidate {
-    distance: OrderedFloat<f32>,
-    pid: PointId,
-}
-
-/// References a `Point` in the `Hnsw`
-///
-/// This can be used to index into the `Hnsw` to refer to the `Point` data.
-#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
-pub struct PointId(u32);
-
-impl PointId {
-    fn invalid() -> Self {
-        PointId(u32::MAX)
-    }
-
-    /// Whether this value represents a valid point
-    pub fn is_valid(self) -> bool {
-        self.0 != u32::MAX
-    }
-}
-
-impl Default for PointId {
-    fn default() -> Self {
-        PointId::invalid()
-    }
-}
-
-impl<P> Index<PointId> for Hnsw<P> {
-    type Output = P;
-
-    fn index(&self, index: PointId) -> &Self::Output {
-        &self.points[index.0 as usize]
-    }
-}
-
-impl<P: Point> Index<PointId> for Vec<P> {
-    type Output = P;
-
-    fn index(&self, index: PointId) -> &Self::Output {
-        &self[index.0 as usize]
-    }
-}
-
-impl<P: Point> Index<PointId> for [P] {
-    type Output = P;
-
-    fn index(&self, index: PointId) -> &Self::Output {
-        &self[index.0 as usize]
-    }
-}
-
-impl Index<PointId> for Vec<ZeroNode> {
-    type Output = ZeroNode;
-
-    fn index(&self, index: PointId) -> &Self::Output {
-        &self[index.0 as usize]
-    }
-}
-
-impl IndexMut<PointId> for Vec<ZeroNode> {
-    fn index_mut(&mut self, index: PointId) -> &mut Self::Output {
-        &mut self[index.0 as usize]
-    }
-}
-
 /// The parameter `M` from the paper
 ///
 /// This should become a generic argument to `Hnsw` when possible.
diff --git a/src/types.rs b/src/types.rs
new file mode 100644
index 0000000..ab42581
--- /dev/null
+++ b/src/types.rs
@@ -0,0 +1,176 @@
+use std::hash::Hash;
+use std::ops::{Index, IndexMut};
+
+use ordered_float::OrderedFloat;
+use rand::rngs::SmallRng;
+use rand::Rng;
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+
+use crate::{Hnsw, Layer, Point, M};
+
+#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
+#[derive(Clone, Copy, Debug, Default)]
+pub(crate) struct UpperNode {
+    /// The nearest neighbors on this layer
+    ///
+    /// This is always kept in sorted order (near to far).
+    pub(crate) nearest: [PointId; M],
+}
+
+impl Layer for [UpperNode] {
+    fn nearest_iter(&self, pid: PointId) -> NearestIter<'_> {
+        NearestIter {
+            nearest: &self[pid.0 as usize].nearest,
+        }
+    }
+}
+
+#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct ZeroNode {
+    /// The nearest neighbors on this layer
+    ///
+    /// This is always kept in sorted order (near to far).
+    pub(crate) nearest: [PointId; M * 2],
+}
+
+impl Default for ZeroNode {
+    fn default() -> ZeroNode {
+        ZeroNode {
+            nearest: [PointId::invalid(); M * 2],
+        }
+    }
+}
+
+impl Layer for [ZeroNode] {
+    fn nearest_iter(&self, pid: PointId) -> NearestIter<'_> {
+        NearestIter {
+            nearest: &self[pid.0 as usize].nearest,
+        }
+    }
+}
+
+pub(crate) struct NearestIter<'a> {
+    nearest: &'a [PointId],
+}
+
+impl<'a> Iterator for NearestIter<'a> {
+    type Item = PointId;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let (&first, rest) = self.nearest.split_first()?;
+        if !first.is_valid() {
+            return None;
+        }
+        self.nearest = rest;
+        Some(first)
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub(crate) struct LayerId(pub usize);
+
+impl LayerId {
+    pub(crate) fn random(ml: f32, rng: &mut SmallRng) -> Self {
+        let layer = rng.gen::<f32>();
+        LayerId((-(layer.ln() * ml)).floor() as usize)
+    }
+
+    pub(crate) fn descend(&self) -> impl Iterator<Item = LayerId> {
+        DescendingLayerIter { next: Some(self.0) }
+    }
+
+    pub(crate) fn is_zero(&self) -> bool {
+        self.0 == 0
+    }
+}
+
+struct DescendingLayerIter {
+    next: Option<usize>,
+}
+
+impl Iterator for DescendingLayerIter {
+    type Item = LayerId;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        Some(LayerId(match self.next? {
+            0 => {
+                self.next = None;
+                0
+            }
+            next => {
+                self.next = Some(next - 1);
+                next
+            }
+        }))
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
+pub(crate) struct Candidate {
+    pub(crate) distance: OrderedFloat<f32>,
+    pub(crate) pid: PointId,
+}
+
+/// References a `Point` in the `Hnsw`
+///
+/// This can be used to index into the `Hnsw` to refer to the `Point` data.
+#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
+#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub struct PointId(pub(crate) u32);
+
+impl PointId {
+    pub(crate) fn invalid() -> Self {
+        PointId(u32::MAX)
+    }
+
+    /// Whether this value represents a valid point
+    pub fn is_valid(self) -> bool {
+        self.0 != u32::MAX
+    }
+}
+
+impl Default for PointId {
+    fn default() -> Self {
+        PointId::invalid()
+    }
+}
+
+impl<P> Index<PointId> for Hnsw<P> {
+    type Output = P;
+
+    fn index(&self, index: PointId) -> &Self::Output {
+        &self.points[index.0 as usize]
+    }
+}
+
+impl<P: Point> Index<PointId> for Vec<P> {
+    type Output = P;
+
+    fn index(&self, index: PointId) -> &Self::Output {
+        &self[index.0 as usize]
+    }
+}
+
+impl<P: Point> Index<PointId> for [P] {
+    type Output = P;
+
+    fn index(&self, index: PointId) -> &Self::Output {
+        &self[index.0 as usize]
+    }
+}
+
+impl Index<PointId> for Vec<ZeroNode> {
+    type Output = ZeroNode;
+
+    fn index(&self, index: PointId) -> &Self::Output {
+        &self[index.0 as usize]
+    }
+}
+
+impl IndexMut<PointId> for Vec<ZeroNode> {
+    fn index_mut(&mut self, index: PointId) -> &mut Self::Output {
+        &mut self[index.0 as usize]
+    }
+}