From 05b633afcae83f6240af3c4e68625887e6dd36f3 Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Sat, 4 Apr 2026 00:13:50 +0200
Subject: [PATCH 01/11] feat: new put implementation

---
 bucket.go               |  22 ++++----
 cuckoo_fuzz_test.go     |   2 +-
 cuckoo_internal_test.go |   2 +-
 cuckoo_test.go          |  30 +++++------
 doc_example_test.go     |   2 +-
 settings.go             |   5 ++
 table.go                | 115 ++++++++++++++++++++++++++--------------
 7 files changed, 111 insertions(+), 67 deletions(-)

diff --git a/bucket.go b/bucket.go
index 6a4171c..8010f3e 100644
--- a/bucket.go
+++ b/bucket.go
@@ -1,12 +1,13 @@
 package cuckoo
 
-type entry[K, V any] struct {
+// An Entry is a key-value pair.
+type Entry[K, V any] struct {
 	key   K
 	value V
 }
 
 type slot[K, V any] struct {
-	entry[K, V]
+	Entry[K, V]
 	occupied bool
 }
 
@@ -48,10 +49,13 @@ func (b *bucket[K, V]) drop(key K) (occupied bool) {
 	return false
 }
 
-func (b *bucket[K, V]) resize(capacity uint64) {
-	b.slots = make([]slot[K, V], capacity)
-	b.capacity = capacity
-	b.size = 0
+func (b *bucket[K, V]) resized(capacity uint64) bucket[K, V] {
+	return bucket[K, V]{
+		slots:    make([]slot[K, V], capacity),
+		capacity: capacity,
+		hash:     b.hash,
+		compare:  b.compare,
+	}
 }
 
 func (b bucket[K, V]) update(key K, value V) (updated bool) {
@@ -69,7 +73,7 @@ func (b bucket[K, V]) update(key K, value V) (updated bool) {
 	return false
 }
 
-func (b *bucket[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
+func (b *bucket[K, V]) insert(insertion Entry[K, V]) (evicted Entry[K, V], eviction bool) {
 	if b.capacity == 0 {
 		return insertion, true
 	}
@@ -77,7 +81,7 @@ func (b *bucket[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], evicti
 	slot := &b.slots[b.location(insertion.key)]
 
 	if !slot.occupied {
-		slot.entry = insertion
+		slot.Entry = insertion
 		slot.occupied = true
 		b.size++
 		return
@@ -88,7 +92,7 @@ func (b *bucket[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], evicti
 		return
 	}
 
-	insertion, slot.entry = slot.entry, insertion
+	insertion, slot.Entry = slot.Entry, insertion
 	return insertion, true
 }
 
diff --git a/cuckoo_fuzz_test.go b/cuckoo_fuzz_test.go
index f849de0..8d30423 100644
--- a/cuckoo_fuzz_test.go
+++ b/cuckoo_fuzz_test.go
@@ -76,7 +76,7 @@ func FuzzInsertLookup(f *testing.F) {
 				_, err = actual.Get(step.key)
 				assert.Error(err)
 			} else {
-				err := actual.Put(step.key, step.value)
+				_, err := actual.Put(step.key, step.value)
 				assert.NoError(err)
 
 				expected[step.key] = step.value
diff --git a/cuckoo_internal_test.go b/cuckoo_internal_test.go
index f2b24a3..ec07056 100644
--- a/cuckoo_internal_test.go
+++ b/cuckoo_internal_test.go
@@ -23,7 +23,7 @@ func TestLoad(t *testing.T) {
 	table := NewTable[int, bool](Capacity(8))
 
 	for i := range 16 {
-		err := table.Put(i, true)
+		_, err := table.Put(i, true)
 		assert.NoError(err)
 		assert.Equal(float64(table.Size())/float64(table.TotalCapacity()), table.load())
 	}
diff --git a/cuckoo_test.go b/cuckoo_test.go
index 131194a..eac1734 100644
--- a/cuckoo_test.go
+++ b/cuckoo_test.go
@@ -25,7 +25,7 @@ func TestAddItem(t *testing.T) {
 	key, value := 0, true
 	table := cuckoo.NewTable[int, bool]()
 
-	err := table.Put(key, value)
+	_, err := table.Put(key, value)
 
 	assert.NoError(err)
 	assert.Equal(1, table.Size())
@@ -38,7 +38,7 @@ func TestPutOverwrite(t *testing.T) {
 	table := cuckoo.NewTable[int, int]()
 	(table.Put(key, value))
 
-	err := table.Put(key, newValue)
+	_, err := table.Put(key, newValue)
 
 	assert.NoError(err)
 	assert.Equal(1, table.Size())
@@ -52,9 +52,9 @@ func TestSameHash(t *testing.T) {
 	hash := func(int) uint64 { return 0 }
 	table := cuckoo.NewCustomTable[int, bool](hash, hash, cuckoo.DefaultEqualFunc[int])
 
-	errA := table.Put(0, true)
-	errB := table.Put(1, true)
-	errC := table.Put(2, true)
+	_, errA := table.Put(0, true)
+	_, errB := table.Put(1, true)
+	_, errC := table.Put(2, true)
 
 	assert.NoError(errA)
 	assert.NoError(errB)
@@ -76,7 +76,7 @@ func TestResizeCapacity(t *testing.T) {
 	)
 
 	for table.TotalCapacity() == 16 {
-		err := table.Put(rand.Int(), true)
+		_, err := table.Put(rand.Int(), true)
 		assert.NoError(err)
 	}
 
@@ -89,7 +89,7 @@ func TestPutMany(t *testing.T) {
 
 	for i := range 1_000 {
 		expected[i] = true
-		err := actual.Put(i, true)
+		_, err := actual.Put(i, true)
 
 		assert.NoError(err)
 	}
@@ -103,7 +103,7 @@ func TestGetMany(t *testing.T) {
 	table := cuckoo.NewTable[int, bool]()
 
 	for i := range 1_000 {
-		err := table.Put(i, true)
+		_, err := table.Put(i, true)
 		assert.NoError(err)
 	}
 
@@ -168,7 +168,7 @@ func TestPutNoCapacity(t *testing.T) {
 		cuckoo.Capacity(0),
 	)
 
-	err := table.Put(key, value)
+	_, err := table.Put(key, value)
 
 	assert.NoError(err)
 	assert.Equal(1, table.Size())
@@ -184,9 +184,9 @@ func TestBadHashCapacity(t *testing.T) {
 		cuckoo.Capacity(20),
 	)
 
-	err1 := table.Put(0, true)
-	err2 := table.Put(1, true)
-	err3 := table.Put(2, true)
+	_, err1 := table.Put(0, true)
+	_, err2 := table.Put(1, true)
+	_, err3 := table.Put(2, true)
 
 	assert.NoError(err1)
 	assert.NoError(err2)
@@ -201,8 +201,8 @@ func TestDropResizeCapacity(t *testing.T) {
 		cuckoo.Capacity(10),
 	)
 
-	err1 := table.Put(0, true)
-	err2 := table.Put(1, true)
+	_, err1 := table.Put(0, true)
+	_, err2 := table.Put(1, true)
 	err3 := table.Drop(1)
 
 	assert.NoError(errors.Join(err1, err2, err3))
@@ -221,7 +221,7 @@ func TestNewTableBy(t *testing.T) {
 		func(u User) string { return u.id },
 	)
 
-	err := table.Put(User{nil, "1", "Robert"}, true)
+	_, err := table.Put(User{nil, "1", "Robert"}, true)
 
 	assert.NoError(err)
 	assert.Equal(1, table.Size())
diff --git a/doc_example_test.go b/doc_example_test.go
index 1fad4ff..86f8e0c 100644
--- a/doc_example_test.go
+++ b/doc_example_test.go
@@ -10,7 +10,7 @@ import (
 func Example_basic() {
 	table := cuckoo.NewTable[int, string]()
 
-	if err := table.Put(1, "Hello, World!"); err != nil {
+	if _, err := table.Put(1, "Hello, World!"); err != nil {
 		fmt.Println("Put error:", err)
 	}
 
diff --git a/settings.go b/settings.go
index fe0408f..425d6ba 100644
--- a/settings.go
+++ b/settings.go
@@ -19,6 +19,11 @@ const DefaultGrowthFactor uint64 = 2
 // [libcuckoo]: https://github.com/efficient/libcuckoo/blob/656714705a055df2b7a605eb3c71586d9da1e119/libcuckoo/cuckoohash_config.hh#L21
 const defaultMinimumLoad float64 = 0.05
 
+// defaultGrowthLimit is the maximum number of times a [Table] can grow in a
+// single [Table.Put], before the library infers it will lead to a stack
+// overflow. The value of '64' was chosen arbirarily.
+const defaultGrowthLimit uint64 = 64
+
 type settings struct {
 	growthFactor  uint64
 	minLoadFactor float64
diff --git a/table.go b/table.go
index 922aa81..e2b35ac 100644
--- a/table.go
+++ b/table.go
@@ -45,30 +45,61 @@ func (t Table[K, V]) load() float64 {
 	return float64(t.Size()) / float64(t.TotalCapacity())
 }
 
-// resize clears all buckets, changes the sizes of them to a specific capacity,
-// and fills them back up again. It is a helper function for [Table.grow] and
-// [Table.shrink]; use them instead.
-func (t *Table[K, V]) resize(capacity uint64) error {
-	entries := make([]entry[K, V], 0, t.Size())
-	for k, v := range t.Entries() {
-		entries = append(entries, entry[K, V]{k, v})
+// insert attempts to put/update an entry in the table, without modifying the
+// size of the table. Returns a displaced entry and 'homeless = true' if an
+// entry could not be placed after exhausting evictions.
+func (t *Table[K, V]) insert(entry Entry[K, V]) (displaced Entry[K, V], homeless bool) {
+	if t.bucketA.update(entry.key, entry.value) {
+		return
 	}
 
-	t.bucketA.resize(capacity)
-	t.bucketB.resize(capacity)
+	if t.bucketB.update(entry.key, entry.value) {
+		return
+	}
 
-	for _, entry := range entries {
-		if err := t.Put(entry.key, entry.value); err != nil {
-			return err
+	for range t.maxEvictions() {
+		if entry, homeless = t.bucketA.insert(entry); !homeless {
+			return
+		}
+
+		if entry, homeless = t.bucketB.insert(entry); !homeless {
+			return
 		}
 	}
 
-	return nil
+	return entry, true
+}
+
+// resized creates an empty copy of the table, with a new capacity for each
+// bucket.
+func (t Table[K, V]) resized(capacity uint64) Table[K, V] {
+	return Table[K, V]{
+		growthFactor:  t.growthFactor,
+		minLoadFactor: t.minLoadFactor,
+		bucketA:       t.bucketA.resized(capacity),
+		bucketB:       t.bucketB.resized(capacity),
+	}
+}
+
+// resize creates a new [Table.resized] with 'capacity', inserts all items into
+// the array, and replaces the current table. It is a helper function for
+// [Table.grow] and [Table.shrink]; use them instead.
+func (t *Table[K, V]) resize(capacity uint64) bool {
+	updated := t.resized(capacity)
+
+	for k, v := range t.Entries() {
+		if _, failed := updated.insert(Entry[K, V]{k, v}); failed {
+			return false
+		}
+	}
+
+	*t = updated
+	return true
 }
 
 // grow increases the table's capacity by the [Table.growthFactor]. If the
 // capacity is 0, it increases it to 1.
-func (t *Table[K, V]) grow() error {
+func (t *Table[K, V]) grow() bool {
 	var newCapacity uint64
 
 	if t.TotalCapacity() == 0 {
@@ -82,7 +113,7 @@ func (t *Table[K, V]) grow() error {
 
 // shrink reduces the table's capacity by the [Table.growthFactor]. It may
 // reduce it down to 0.
-func (t *Table[K, V]) shrink() error {
+func (t *Table[K, V]) shrink() bool {
 	return t.resize(t.bucketA.capacity / t.growthFactor)
 }
 
@@ -106,36 +137,38 @@ func (t Table[K, V]) Has(key K) (exists bool) {
 	return err == nil
 }
 
-// Put sets the value for a key. Returns error if its value cannot be set.
-func (t *Table[K, V]) Put(key K, value V) (err error) {
-	if t.bucketA.update(key, value) {
-		return nil
-	}
+// Put sets the value for a key. If it cannot be set, an error is returned,
+// along with the last displaced entry.
+//
+// On failure, the returned entry and the current table contents together
+// preserve all previously inserted entries and the attempted entry.
+func (t *Table[K, V]) Put(key K, value V) (displaced Entry[K, V], err error) {
+	var (
+		entry    = Entry[K, V]{key, value}
+		homeless bool
+	)
 
-	if t.bucketB.update(key, value) {
-		return nil
-	}
-
-	entry, eviction := entry[K, V]{key, value}, false
-	for range t.maxEvictions() {
-		if entry, eviction = t.bucketA.evict(entry); !eviction {
-			return nil
+	for range defaultGrowthLimit {
+		if entry, homeless = t.insert(entry); !homeless {
+			return
 		}
 
-		if entry, eviction = t.bucketB.evict(entry); !eviction {
-			return nil
+		// Both this and the growth limit are necessary: this catches bad hashes
+		// early when the table is sparse, while the latter catches cases where
+		// growing never helps.
+		if t.load() < t.minLoadFactor {
+			return entry, fmt.Errorf("bad hash: resize on load %d/%d", t.Size(), t.TotalCapacity())
+		}
+
+		// It is theoretically possible to have a table with a larger capacity
+		// that is valid. But this chance is astronomically small, so we ignore
+		// it in this implementation.
+		if grew := t.grow(); !grew {
+			return entry, fmt.Errorf("bad hash: could not redistribute entries into larger table")
 		}
 	}
 
-	if t.load() < t.minLoadFactor {
-		return fmt.Errorf("bad hash: resize on load %d/%d = %f", t.Size(), t.TotalCapacity(), t.load())
-	}
-
-	if err := t.grow(); err != nil {
-		return err
-	}
-
-	return t.Put(entry.key, entry.value)
+	return entry, fmt.Errorf("bad hash: could not place entry after %d resizes", defaultGrowthLimit)
 }
 
 // Drop removes a value for a key in the table. Returns an error if its value
@@ -145,7 +178,9 @@ func (t *Table[K, V]) Drop(key K) (err error) {
 	t.bucketB.drop(key)
 
 	if t.load() < t.minLoadFactor {
-		return t.shrink()
+		// The error is not handled here, because table-shrinking is an internal
+		// optimization.
+		t.shrink()
 	}
 
 	return nil
-- 
2.49.1


From afead3330a48572576d951c73b4c00330cad79ad Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Sat, 4 Apr 2026 00:20:34 +0200
Subject: [PATCH 02/11] feat: drop item returns bool, whether item existed

---
 cuckoo_fuzz_test.go |  7 ++++---
 cuckoo_test.go      | 15 +++++++--------
 table.go            | 11 +++++------
 3 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/cuckoo_fuzz_test.go b/cuckoo_fuzz_test.go
index 8d30423..51aa112 100644
--- a/cuckoo_fuzz_test.go
+++ b/cuckoo_fuzz_test.go
@@ -68,12 +68,13 @@ func FuzzInsertLookup(f *testing.F) {
 
 		for _, step := range scenario.steps {
 			if step.drop {
-				err := actual.Drop(step.key)
-				assert.NoError(err)
+				ok := actual.Drop(step.key)
+				_, has := expected[step.key]
+				assert.Equal(ok, has)
 
 				delete(expected, step.key)
 
-				_, err = actual.Get(step.key)
+				_, err := actual.Get(step.key)
 				assert.Error(err)
 			} else {
 				_, err := actual.Put(step.key, step.value)
diff --git a/cuckoo_test.go b/cuckoo_test.go
index eac1734..738e501 100644
--- a/cuckoo_test.go
+++ b/cuckoo_test.go
@@ -124,9 +124,9 @@ func TestDropExistingItem(t *testing.T) {
 	table := cuckoo.NewTable[int, bool]()
 	(table.Put(key, value))
 
-	err := table.Drop(key)
+	had := table.Drop(key)
 
-	assert.NoError(err)
+	assert.True(had)
 	assert.Equal(0, table.Size())
 	assert.False(table.Has(key))
 }
@@ -136,9 +136,9 @@ func TestDropNoItem(t *testing.T) {
 	key := 0
 	table := cuckoo.NewTable[int, bool]()
 
-	err := table.Drop(key)
+	had := table.Drop(key)
 
-	assert.NoError(err)
+	assert.False(had)
 	assert.Equal(0, table.Size())
 	assert.False(table.Has(key))
 }
@@ -152,10 +152,9 @@ func TestDropItemCapacity(t *testing.T) {
 	)
 
 	startingCapacity := table.TotalCapacity()
-	err := table.Drop(key)
+	table.Drop(key)
 	endingCapacity := table.TotalCapacity()
 
-	assert.NoError(err)
 	assert.Equal(0, table.Size())
 	assert.Equal(uint64(128), startingCapacity)
 	assert.Equal(uint64(64), endingCapacity)
@@ -203,9 +202,9 @@ func TestDropResizeCapacity(t *testing.T) {
 
 	_, err1 := table.Put(0, true)
 	_, err2 := table.Put(1, true)
-	err3 := table.Drop(1)
+	table.Drop(1)
 
-	assert.NoError(errors.Join(err1, err2, err3))
+	assert.NoError(errors.Join(err1, err2))
 	assert.Equal(uint64(20), table.TotalCapacity())
 }
 
diff --git a/table.go b/table.go
index e2b35ac..5aa0823 100644
--- a/table.go
+++ b/table.go
@@ -171,11 +171,10 @@ func (t *Table[K, V]) Put(key K, value V) (displaced Entry[K, V], err error) {
 	return entry, fmt.Errorf("bad hash: could not place entry after %d resizes", defaultGrowthLimit)
 }
 
-// Drop removes a value for a key in the table. Returns an error if its value
-// cannot be removed.
-func (t *Table[K, V]) Drop(key K) (err error) {
-	t.bucketA.drop(key)
-	t.bucketB.drop(key)
+// Drop removes a value for a key in the table. Returns whether the key had
+// existed.
+func (t *Table[K, V]) Drop(key K) bool {
+	occupied := t.bucketA.drop(key) || t.bucketB.drop(key)
 
 	if t.load() < t.minLoadFactor {
 		// The error is not handled here, because table-shrinking is an internal
@@ -183,7 +182,7 @@ func (t *Table[K, V]) Drop(key K) (err error) {
 		t.shrink()
 	}
 
-	return nil
+	return occupied
 }
 
 // Entries returns an unordered sequence of all key-value pairs in the table.
-- 
2.49.1


From ca66ccd04054443f60a61bab0bb4a8aa3937c23d Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Sat, 4 Apr 2026 00:38:27 +0200
Subject: [PATCH 03/11] fix: public facing key/value fields in entry

---
 bucket.go | 18 +++++++++---------
 table.go  |  8 ++++----
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/bucket.go b/bucket.go
index 8010f3e..3a3b1da 100644
--- a/bucket.go
+++ b/bucket.go
@@ -2,8 +2,8 @@ package cuckoo
 
 // An Entry is a key-value pair.
 type Entry[K, V any] struct {
-	key   K
-	value V
+	Key   K
+	Value V
 }
 
 type slot[K, V any] struct {
@@ -30,7 +30,7 @@ func (b bucket[K, V]) get(key K) (value V, found bool) {
 	}
 
 	slot := b.slots[b.location(key)]
-	return slot.value, slot.occupied && b.compare(slot.key, key)
+	return slot.Value, slot.occupied && b.compare(slot.Key, key)
 }
 
 func (b *bucket[K, V]) drop(key K) (occupied bool) {
@@ -40,7 +40,7 @@ func (b *bucket[K, V]) drop(key K) (occupied bool) {
 
 	slot := &b.slots[b.location(key)]
 
-	if slot.occupied && b.compare(slot.key, key) {
+	if slot.occupied && b.compare(slot.Key, key) {
 		slot.occupied = false
 		b.size--
 		return true
@@ -65,8 +65,8 @@ func (b bucket[K, V]) update(key K, value V) (updated bool) {
 
 	slot := &b.slots[b.location(key)]
 
-	if slot.occupied && b.compare(slot.key, key) {
-		slot.value = value
+	if slot.occupied && b.compare(slot.Key, key) {
+		slot.Value = value
 		return true
 	}
 
@@ -78,7 +78,7 @@ func (b *bucket[K, V]) insert(insertion Entry[K, V]) (evicted Entry[K, V], evict
 		return insertion, true
 	}
 
-	slot := &b.slots[b.location(insertion.key)]
+	slot := &b.slots[b.location(insertion.Key)]
 
 	if !slot.occupied {
 		slot.Entry = insertion
@@ -87,8 +87,8 @@ func (b *bucket[K, V]) insert(insertion Entry[K, V]) (evicted Entry[K, V], evict
 		return
 	}
 
-	if b.compare(slot.key, insertion.key) {
-		slot.value = insertion.value
+	if b.compare(slot.Key, insertion.Key) {
+		slot.Value = insertion.Value
 		return
 	}
 
diff --git a/table.go b/table.go
index 5aa0823..fbfde2b 100644
--- a/table.go
+++ b/table.go
@@ -49,11 +49,11 @@ func (t Table[K, V]) load() float64 {
 // size of the table. Returns a displaced entry and 'homeless = true' if an
 // entry could not be placed after exhausting evictions.
 func (t *Table[K, V]) insert(entry Entry[K, V]) (displaced Entry[K, V], homeless bool) {
-	if t.bucketA.update(entry.key, entry.value) {
+	if t.bucketA.update(entry.Key, entry.Value) {
 		return
 	}
 
-	if t.bucketB.update(entry.key, entry.value) {
+	if t.bucketB.update(entry.Key, entry.Value) {
 		return
 	}
 
@@ -190,7 +190,7 @@ func (t Table[K, V]) Entries() iter.Seq2[K, V] {
 	return func(yield func(K, V) bool) {
 		for _, slot := range t.bucketA.slots {
 			if slot.occupied {
-				if !yield(slot.key, slot.value) {
+				if !yield(slot.Key, slot.Value) {
 					return
 				}
 			}
@@ -198,7 +198,7 @@ func (t Table[K, V]) Entries() iter.Seq2[K, V] {
 
 		for _, slot := range t.bucketB.slots {
 			if slot.occupied {
-				if !yield(slot.key, slot.value) {
+				if !yield(slot.Key, slot.Value) {
 					return
 				}
 			}
-- 
2.49.1


From 78f7d01d5f41f5ba9ba6e9da6a99b7c4a475357a Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Thu, 16 Apr 2026 00:00:37 -0400
Subject: [PATCH 04/11] revert: forgot about b -> t

---
 subtable.go | 46 +++++++++++++++++++++++-----------------------
 1 file changed, 23 insertions(+), 23 deletions(-)

diff --git a/subtable.go b/subtable.go
index f502bcf..53a9785 100644
--- a/subtable.go
+++ b/subtable.go
@@ -20,52 +20,52 @@ type subtable[K, V any] struct {
 
 // location determines where in the bucket a certain key would be placed. If the
 // capacity is 0, this will panic.
-func (b *subtable[K, V]) location(key K) uint64 {
-	return b.hash(key) % b.capacity
+func (t *subtable[K, V]) location(key K) uint64 {
+	return t.hash(key) % t.capacity
 }
 
-func (b *subtable[K, V]) get(key K) (value V, found bool) {
-	if b.capacity == 0 {
+func (t *subtable[K, V]) get(key K) (value V, found bool) {
+	if t.capacity == 0 {
 		return
 	}
 
-	slot := b.slots[b.location(key)]
-	return slot.Value, slot.occupied && b.compare(slot.Key, key)
+	slot := t.slots[t.location(key)]
+	return slot.Value, slot.occupied && t.compare(slot.Key, key)
 }
 
-func (b *subtable[K, V]) drop(key K) (occupied bool) {
-	if b.capacity == 0 {
+func (t *subtable[K, V]) drop(key K) (occupied bool) {
+	if t.capacity == 0 {
 		return
 	}
 
-	slot := &b.slots[b.location(key)]
+	slot := &t.slots[t.location(key)]
 
-	if slot.occupied && b.compare(slot.Key, key) {
+	if slot.occupied && t.compare(slot.Key, key) {
 		slot.occupied = false
-		b.size--
+		t.size--
 		return true
 	}
 
 	return false
 }
 
-func (b *subtable[K, V]) resized(capacity uint64) *subtable[K, V] {
+func (t *subtable[K, V]) resized(capacity uint64) *subtable[K, V] {
 	return &subtable[K, V]{
 		slots:    make([]slot[K, V], capacity),
 		capacity: capacity,
-		hash:     b.hash,
-		compare:  b.compare,
+		hash:     t.hash,
+		compare:  t.compare,
 	}
 }
 
-func (b *subtable[K, V]) update(key K, value V) (updated bool) {
-	if b.capacity == 0 {
+func (t *subtable[K, V]) update(key K, value V) (updated bool) {
+	if t.capacity == 0 {
 		return
 	}
 
-	slot := &b.slots[b.location(key)]
+	slot := &t.slots[t.location(key)]
 
-	if slot.occupied && b.compare(slot.Key, key) {
+	if slot.occupied && t.compare(slot.Key, key) {
 		slot.Value = value
 		return true
 	}
@@ -73,21 +73,21 @@ func (b *subtable[K, V]) update(key K, value V) (updated bool) {
 	return false
 }
 
-func (b *subtable[K, V]) insert(insertion Entry[K, V]) (evicted Entry[K, V], eviction bool) {
-	if b.capacity == 0 {
+func (t *subtable[K, V]) insert(insertion Entry[K, V]) (evicted Entry[K, V], eviction bool) {
+	if t.capacity == 0 {
 		return insertion, true
 	}
 
-	slot := &b.slots[b.location(insertion.Key)]
+	slot := &t.slots[t.location(insertion.Key)]
 
 	if !slot.occupied {
 		slot.Entry = insertion
 		slot.occupied = true
-		b.size++
+		t.size++
 		return
 	}
 
-	if b.compare(slot.Key, insertion.Key) {
+	if t.compare(slot.Key, insertion.Key) {
 		slot.Value = insertion.Value
 		return
 	}
-- 
2.49.1


From fce632545451cb4c8de26ddd14b40b45d68035e9 Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Thu, 16 Apr 2026 00:01:17 -0400
Subject: [PATCH 05/11] docs: naming of subtable.location was outdated

---
 subtable.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/subtable.go b/subtable.go
index 53a9785..7ed86d9 100644
--- a/subtable.go
+++ b/subtable.go
@@ -18,8 +18,8 @@ type subtable[K, V any] struct {
 	compare        EqualFunc[K]
 }
 
-// location determines where in the bucket a certain key would be placed. If the
-// capacity is 0, this will panic.
+// location determines where in the subtable a certain key would be placed. If
+// the capacity is 0, this will panic.
 func (t *subtable[K, V]) location(key K) uint64 {
 	return t.hash(key) % t.capacity
 }
-- 
2.49.1


From 24b646c5dc2818212e11af76b06e2f06a275352f Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Thu, 16 Apr 2026 00:06:09 -0400
Subject: [PATCH 06/11] feat: use bad hash sentinel error

---
 table.go | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/table.go b/table.go
index 322e950..c869814 100644
--- a/table.go
+++ b/table.go
@@ -173,18 +173,18 @@ func (t *Table[K, V]) Put(key K, value V) (displaced Entry[K, V], err error) {
 		// early when the table is sparse, while the latter catches cases where
 		// growing never helps.
 		if t.load() < t.minLoadFactor {
-			return entry, fmt.Errorf("bad hash: resize on load %d/%d", t.Size(), t.TotalCapacity())
+			return entry, fmt.Errorf("hash functions produced a cycle at load %d/%d: %w", t.Size(), t.TotalCapacity(), ErrBadHash)
 		}
 
 		// It is theoretically possible to have a table with a larger capacity
 		// that is valid. But this chance is astronomically small, so we ignore
 		// it in this implementation.
 		if grew := t.grow(); !grew {
-			return entry, fmt.Errorf("bad hash: could not redistribute entries into larger table")
+			return entry, fmt.Errorf("could not redistribute entries into larger table: %w", ErrBadHash)
 		}
 	}
 
-	return entry, fmt.Errorf("bad hash: could not place entry after %d resizes", defaultGrowthLimit)
+	return entry, fmt.Errorf("could not place entry after %d resizes: %w", defaultGrowthLimit, ErrBadHash)
 }
 
 // Drop removes a value for a key in the table. Returns whether the key had
-- 
2.49.1


From 5452c02d4e33aedb9020ab706d39bd441f7c3598 Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Thu, 16 Apr 2026 20:33:50 -0400
Subject: [PATCH 07/11] fix: assertion in fuzz test incorrect

---
 cuckoo_fuzz_test.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cuckoo_fuzz_test.go b/cuckoo_fuzz_test.go
index 7c6af28..f96bc6e 100644
--- a/cuckoo_fuzz_test.go
+++ b/cuckoo_fuzz_test.go
@@ -75,7 +75,7 @@ func FuzzInsertLookup(f *testing.F) {
 				delete(expected, step.key)
 
 				_, ok = actual.Get(step.key)
-				assert.True(ok)
+				assert.False(ok)
 			} else {
 				_, err := actual.Put(step.key, step.value)
 				assert.NoError(err)
-- 
2.49.1


From d13adcaa4937a4ba083b4eee5926960b7e385aab Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Thu, 16 Apr 2026 21:05:43 -0400
Subject: [PATCH 08/11] docs: note that the table isnt a source of truth

---
 doc.go   | 3 +++
 table.go | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/doc.go b/doc.go
index 3be8bfc..2d1f62f 100644
--- a/doc.go
+++ b/doc.go
@@ -5,5 +5,8 @@
 // a table with any key type using [NewCustom]. Custom [Hash] functions and
 // key comparison are also supported.
 //
+// NOTE: The [Table] is a look-up structure, and not a source of truth. If
+// [ErrBadHash] occurs, the data cannot be restored.
+//
 // See more: https://en.wikipedia.org/wiki/Cuckoo_hashing
 package cuckoo
diff --git a/table.go b/table.go
index c869814..105d36e 100644
--- a/table.go
+++ b/table.go
@@ -9,7 +9,7 @@ import (
 )
 
 // ErrBadHash occurs when the hashes given to a [Table] cause too many key
-// collisions. Try rebuilding the table using:
+// collisions. Discard the old table, rebuild it from your source data, and try:
 //
 //  1. Different hash seeds. Equal seeds produce equal hash functions, which
 //     always cycle.
-- 
2.49.1


From 24df23218c8a550aeda54612e19cb42a60374724 Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Thu, 16 Apr 2026 21:11:22 -0400
Subject: [PATCH 09/11] revert!: old put contract

---
 table.go | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/table.go b/table.go
index 105d36e..1f16fdc 100644
--- a/table.go
+++ b/table.go
@@ -153,12 +153,8 @@ func (t *Table[K, V]) Has(key K) (exists bool) {
 	return
 }
 
-// Put sets the value for a key. If it cannot be set, an error is returned,
-// along with the last displaced entry.
-//
-// On failure, the returned entry and the current table contents together
-// preserve all previously inserted entries and the attempted entry.
-func (t *Table[K, V]) Put(key K, value V) (displaced Entry[K, V], err error) {
+// Put sets the value for a key. If it cannot be set, an error is returned.
+func (t *Table[K, V]) Put(key K, value V) (err error) {
 	var (
 		entry    = Entry[K, V]{key, value}
 		homeless bool
@@ -173,18 +169,18 @@ func (t *Table[K, V]) Put(key K, value V) (displaced Entry[K, V], err error) {
 		// early when the table is sparse, while the latter catches cases where
 		// growing never helps.
 		if t.load() < t.minLoadFactor {
-			return entry, fmt.Errorf("hash functions produced a cycle at load %d/%d: %w", t.Size(), t.TotalCapacity(), ErrBadHash)
+			return fmt.Errorf("hash functions produced a cycle at load %d/%d: %w", t.Size(), t.TotalCapacity(), ErrBadHash)
 		}
 
 		// It is theoretically possible to have a table with a larger capacity
 		// that is valid. But this chance is astronomically small, so we ignore
 		// it in this implementation.
 		if grew := t.grow(); !grew {
-			return entry, fmt.Errorf("could not redistribute entries into larger table: %w", ErrBadHash)
+			return fmt.Errorf("could not redistribute entries into larger table: %w", ErrBadHash)
 		}
 	}
 
-	return entry, fmt.Errorf("could not place entry after %d resizes: %w", defaultGrowthLimit, ErrBadHash)
+	return fmt.Errorf("could not place entry after %d resizes: %w", defaultGrowthLimit, ErrBadHash)
 }
 
 // Drop removes a value for a key in the table. Returns whether the key had
-- 
2.49.1


From b395d6e1f47d01136fdbf4befc0d9183e6a9e8c0 Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Thu, 16 Apr 2026 21:12:39 -0400
Subject: [PATCH 10/11] fix: tests were out of date

---
 cuckoo_fuzz_test.go     |  2 +-
 cuckoo_internal_test.go |  2 +-
 cuckoo_test.go          | 30 +++++++++++++++---------------
 doc_example_test.go     |  2 +-
 4 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/cuckoo_fuzz_test.go b/cuckoo_fuzz_test.go
index f96bc6e..a6a5672 100644
--- a/cuckoo_fuzz_test.go
+++ b/cuckoo_fuzz_test.go
@@ -77,7 +77,7 @@ func FuzzInsertLookup(f *testing.F) {
 				_, ok = actual.Get(step.key)
 				assert.False(ok)
 			} else {
-				_, err := actual.Put(step.key, step.value)
+				err := actual.Put(step.key, step.value)
 				assert.NoError(err)
 
 				expected[step.key] = step.value
diff --git a/cuckoo_internal_test.go b/cuckoo_internal_test.go
index d34852a..461f4d7 100644
--- a/cuckoo_internal_test.go
+++ b/cuckoo_internal_test.go
@@ -23,7 +23,7 @@ func TestLoad(t *testing.T) {
 	table := New[int, bool](Capacity(8))
 
 	for i := range 16 {
-		_, err := table.Put(i, true)
+		err := table.Put(i, true)
 		assert.NoError(err)
 		assert.Equal(float64(table.Size())/float64(table.TotalCapacity()), table.load())
 	}
diff --git a/cuckoo_test.go b/cuckoo_test.go
index d0d1ae3..08394ad 100644
--- a/cuckoo_test.go
+++ b/cuckoo_test.go
@@ -25,7 +25,7 @@ func TestAddItem(t *testing.T) {
 	key, value := 0, true
 	table := cuckoo.New[int, bool]()
 
-	_, err := table.Put(key, value)
+	err := table.Put(key, value)
 
 	assert.NoError(err)
 	assert.Equal(1, table.Size())
@@ -38,7 +38,7 @@ func TestPutOverwrite(t *testing.T) {
 	table := cuckoo.New[int, int]()
 	(table.Put(key, value))
 
-	_, err := table.Put(key, newValue)
+	err := table.Put(key, newValue)
 
 	assert.NoError(err)
 	assert.Equal(1, table.Size())
@@ -52,9 +52,9 @@ func TestSameHash(t *testing.T) {
 	hash := func(int) uint64 { return 0 }
 	table := cuckoo.NewCustom[int, bool](hash, hash, cuckoo.DefaultEqualFunc[int])
 
-	_, errA := table.Put(0, true)
-	_, errB := table.Put(1, true)
-	_, errC := table.Put(2, true)
+	errA := table.Put(0, true)
+	errB := table.Put(1, true)
+	errC := table.Put(2, true)
 
 	assert.NoError(errA)
 	assert.NoError(errB)
@@ -76,7 +76,7 @@ func TestResizeCapacity(t *testing.T) {
 	)
 
 	for table.TotalCapacity() == 16 {
-		_, err := table.Put(rand.Int(), true)
+		err := table.Put(rand.Int(), true)
 		assert.NoError(err)
 	}
 
@@ -89,7 +89,7 @@ func TestPutMany(t *testing.T) {
 
 	for i := range 1_000 {
 		expected[i] = true
-		_, err := actual.Put(i, true)
+		err := actual.Put(i, true)
 
 		assert.NoError(err)
 	}
@@ -103,7 +103,7 @@ func TestGetMany(t *testing.T) {
 	table := cuckoo.New[int, bool]()
 
 	for i := range 1_000 {
-		_, err := table.Put(i, true)
+		err := table.Put(i, true)
 		assert.NoError(err)
 	}
 
@@ -167,7 +167,7 @@ func TestPutNoCapacity(t *testing.T) {
 		cuckoo.Capacity(0),
 	)
 
-	_, err := table.Put(key, value)
+	err := table.Put(key, value)
 
 	assert.NoError(err)
 	assert.Equal(1, table.Size())
@@ -183,9 +183,9 @@ func TestBadHashCapacity(t *testing.T) {
 		cuckoo.Capacity(20),
 	)
 
-	_, err1 := table.Put(0, true)
-	_, err2 := table.Put(1, true)
-	_, err3 := table.Put(2, true)
+	err1 := table.Put(0, true)
+	err2 := table.Put(1, true)
+	err3 := table.Put(2, true)
 
 	assert.NoError(err1)
 	assert.NoError(err2)
@@ -200,8 +200,8 @@ func TestDropResizeCapacity(t *testing.T) {
 		cuckoo.Capacity(10),
 	)
 
-	_, err1 := table.Put(0, true)
-	_, err2 := table.Put(1, true)
+	err1 := table.Put(0, true)
+	err2 := table.Put(1, true)
 	table.Drop(1)
 
 	assert.NoError(errors.Join(err1, err2))
@@ -218,7 +218,7 @@ func TestNewTableBy(t *testing.T) {
 	assert := assert.New(t)
 	table := cuckoo.NewBy[User, bool](func(u User) string { return u.id })
 
-	_, err := table.Put(User{nil, "1", "Robert"}, true)
+	err := table.Put(User{nil, "1", "Robert"}, true)
 
 	assert.NoError(err)
 	assert.Equal(1, table.Size())
diff --git a/doc_example_test.go b/doc_example_test.go
index 63ea8f1..3671857 100644
--- a/doc_example_test.go
+++ b/doc_example_test.go
@@ -10,7 +10,7 @@ import (
 func Example_basic() {
 	table := cuckoo.New[int, string]()
 
-	if _, err := table.Put(1, "Hello, World!"); err != nil {
+	if err := table.Put(1, "Hello, World!"); err != nil {
 		fmt.Println("Put error:", err)
 	}
 
-- 
2.49.1


From 7b45099cea72786699319b8253dbaceeea44bbad Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Thu, 16 Apr 2026 21:15:11 -0400
Subject: [PATCH 11/11] revert: Entry -> entry bc Put() doesnt use it

---
 subtable.go | 30 +++++++++++++++---------------
 table.go    | 14 +++++++-------
 2 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/subtable.go b/subtable.go
index 7ed86d9..e6d591a 100644
--- a/subtable.go
+++ b/subtable.go
@@ -1,13 +1,13 @@
 package cuckoo
 
-// An Entry is a key-value pair.
-type Entry[K, V any] struct {
-	Key   K
-	Value V
+// An entry is a key-value pair.
+type entry[K, V any] struct {
+	key   K
+	value V
 }
 
 type slot[K, V any] struct {
-	Entry[K, V]
+	entry[K, V]
 	occupied bool
 }
 
@@ -30,7 +30,7 @@ func (t *subtable[K, V]) get(key K) (value V, found bool) {
 	}
 
 	slot := t.slots[t.location(key)]
-	return slot.Value, slot.occupied && t.compare(slot.Key, key)
+	return slot.value, slot.occupied && t.compare(slot.key, key)
 }
 
 func (t *subtable[K, V]) drop(key K) (occupied bool) {
@@ -40,7 +40,7 @@ func (t *subtable[K, V]) drop(key K) (occupied bool) {
 
 	slot := &t.slots[t.location(key)]
 
-	if slot.occupied && t.compare(slot.Key, key) {
+	if slot.occupied && t.compare(slot.key, key) {
 		slot.occupied = false
 		t.size--
 		return true
@@ -65,34 +65,34 @@ func (t *subtable[K, V]) update(key K, value V) (updated bool) {
 
 	slot := &t.slots[t.location(key)]
 
-	if slot.occupied && t.compare(slot.Key, key) {
-		slot.Value = value
+	if slot.occupied && t.compare(slot.key, key) {
+		slot.value = value
 		return true
 	}
 
 	return false
 }
 
-func (t *subtable[K, V]) insert(insertion Entry[K, V]) (evicted Entry[K, V], eviction bool) {
+func (t *subtable[K, V]) insert(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
 	if t.capacity == 0 {
 		return insertion, true
 	}
 
-	slot := &t.slots[t.location(insertion.Key)]
+	slot := &t.slots[t.location(insertion.key)]
 
 	if !slot.occupied {
-		slot.Entry = insertion
+		slot.entry = insertion
 		slot.occupied = true
 		t.size++
 		return
 	}
 
-	if t.compare(slot.Key, insertion.Key) {
-		slot.Value = insertion.Value
+	if t.compare(slot.key, insertion.key) {
+		slot.value = insertion.value
 		return
 	}
 
-	insertion, slot.Entry = slot.Entry, insertion
+	insertion, slot.entry = slot.entry, insertion
 	return insertion, true
 }
 
diff --git a/table.go b/table.go
index 1f16fdc..b0c6d78 100644
--- a/table.go
+++ b/table.go
@@ -57,12 +57,12 @@ func (t *Table[K, V]) load() float64 {
 // insert attempts to put/update an entry in the table, without modifying the
 // size of the table. Returns a displaced entry and 'homeless = true' if an
 // entry could not be placed after exhausting evictions.
-func (t *Table[K, V]) insert(entry Entry[K, V]) (displaced Entry[K, V], homeless bool) {
-	if t.tableA.update(entry.Key, entry.Value) {
+func (t *Table[K, V]) insert(entry entry[K, V]) (displaced entry[K, V], homeless bool) {
+	if t.tableA.update(entry.key, entry.value) {
 		return
 	}
 
-	if t.tableB.update(entry.Key, entry.Value) {
+	if t.tableB.update(entry.key, entry.value) {
 		return
 	}
 
@@ -97,7 +97,7 @@ func (t *Table[K, V]) resize(capacity uint64) bool {
 	updated := t.resized(capacity)
 
 	for k, v := range t.Entries() {
-		if _, failed := updated.insert(Entry[K, V]{k, v}); failed {
+		if _, failed := updated.insert(entry[K, V]{k, v}); failed {
 			return false
 		}
 	}
@@ -156,7 +156,7 @@ func (t *Table[K, V]) Has(key K) (exists bool) {
 // Put sets the value for a key. If it cannot be set, an error is returned.
 func (t *Table[K, V]) Put(key K, value V) (err error) {
 	var (
-		entry    = Entry[K, V]{key, value}
+		entry    = entry[K, V]{key, value}
 		homeless bool
 	)
 
@@ -202,7 +202,7 @@ func (t *Table[K, V]) Entries() iter.Seq2[K, V] {
 	return func(yield func(K, V) bool) {
 		for _, slot := range t.tableA.slots {
 			if slot.occupied {
-				if !yield(slot.Key, slot.Value) {
+				if !yield(slot.key, slot.value) {
 					return
 				}
 			}
@@ -210,7 +210,7 @@ func (t *Table[K, V]) Entries() iter.Seq2[K, V] {
 
 		for _, slot := range t.tableB.slots {
 			if slot.occupied {
-				if !yield(slot.Key, slot.Value) {
+				if !yield(slot.key, slot.value) {
 					return
 				}
 			}
-- 
2.49.1