fix: public facing key/value fields in entry

## Description

The `cuckoo.MinimumLoad()` option was not a very useful option, and prone to error. By removing the ability to modify it, and setting it to something reasonable (like 5%), we can remove a whole set of errors that the user may stumble into.

## Changes

- Remove `MinimumLoad()` option.
- Privated `DefaultMinimumLoad`.

### Design Decisions

- `DefaultMinimumLoad` should be privated because it is no longer an option. The user should not need to interact with it.

## Checklist

- [x] Tests pass
- [x] Docs updated

Reviewed-on: #17

.gitea/ISSUE_TEMPLATE/BUG_REPORT.yml

@@ -0,0 +1,26 @@
+# yaml-language-server: $schema=https://www.schemastore.org/gitea-issue-forms.json
+name: 🐛 Bug Report
+about: Report a bug in this project
+title: "[BUG]: "
+body:
+  - type: textarea
+    id: context
+    attributes:
+      label: Context
+      placeholder: What circumstances led to the bug?
+    validations:
+      required: true
+  - type: textarea
+    id: expected-behavior
+    attributes:
+      label: Expected Behavior
+      placeholder: What did you expect would happen?
+    validations:
+      required: true
+  - type: textarea
+    id: actual-behavior
+    attributes:
+      label: Actual Behavior
+      placeholder: What happened, and why was it unexpected?
+    validations:
+      required: true

.gitea/ISSUE_TEMPLATE/FEATURE_REQUEST.yml

@@ -0,0 +1,37 @@
+# 'Feature Request Template' By @cheehwatang
+# https://github.com/cheehwatang/.github/blob/master/.github/ISSUE_TEMPLATE/feature_request.yml
+#
+# yaml-language-server: $schema=https://www.schemastore.org/gitea-issue-forms.json
+name: ✨ Feature Request
+about: Suggest an idea for this project
+title: "[FEATURE]: "
+body:
+  - type: dropdown
+    attributes:
+      multiple: false
+      label: Feature Type
+      options:
+        - "✨ New Feature"
+        - "📝 Documentation"
+        - "🎨 Style and UI"
+        - "🔨 Code Refactor"
+        - "⚡ Performance Improvements"
+        - "✅ New Test"
+    validations:
+      required: true
+  - type: textarea
+    id: description
+    attributes:
+      label: Description
+      placeholder: |
+        Give us a brief description of the feature or enhancement you would
+        like!
+    validations:
+      required: true
+  - type: textarea
+    id: additional-information
+    attributes:
+      label: Additional Information
+      placeholder: |
+        Give us some additional information on the feature request like proposed
+        solutions, links, screenshots, etc.

.gitea/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,2 @@
+# yaml-language-server: $schema=https://www.schemastore.org/gitea-issue-config.json
+blank_issues_enabled: false

.gitea/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,17 @@
+---
+name: "New Pull Request"
+about: "Standard PR template"
+title: ""
+ref: "main"
+---
+
+## Description
+
+## Changes
+
+### Design Decisions
+
+## Checklist
+
+- [ ] Tests pass
+- [ ] Docs updated

.gitea/workflows/ci.yml

@@ -6,8 +6,21 @@ on:
   pull_request:
 
 jobs:
-  lint:
-    name: Golang Lint
+  check-pr-title:
+    name: Check PR Title
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+    env:
+      TITLE: ${{ gitea.event.pull_request.title }}
+    steps:
+      - run: |
+          if ! echo "$TITLE" | grep -qE '^(WIP: )?(feat|fix|docs|chore|ci|test|refactor|perf|build|style|revert)(\(.+\))?(!)?: .+'; then
+            echo "::error::Pull Request title must follow conventional commits"
+            exit 1
+          fi
+
+  lint-go:
+    name: Go Lint
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
@@ -23,7 +36,31 @@ jobs:
         with:
           version: latest
 
-  unit-test:
+  lint-makefile:
+    name: Makefile Lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+
+      - name: Install gremlins
+        run: go install github.com/checkmake/checkmake/cmd/checkmake@latest
+
+      - name: Run mutation tests
+        run: make lint-makefile
+
+  lint-markdown:
+    name: Markdown Lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: DavidAnson/markdownlint-cli2-action@v19
+
+  test-unit:
     name: Unit Tests
     runs-on: ubuntu-latest
     steps:
@@ -34,9 +71,9 @@ jobs:
           go-version-file: go.mod
 
       - name: Run unit tests
-        run: go test ./... -cover -v
+        run: make test-unit
 
-  fuzz-test:
+  test-fuzz:
     name: Fuzz Tests
     runs-on: ubuntu-latest
     steps:
@@ -47,12 +84,9 @@ jobs:
           go-version-file: go.mod
 
       - name: Run fuzz tests
-        run: |
-          for func in $(grep -r --include='*_test.go' -oh 'func Fuzz\w*' . | sed 's/func //'); do
-            go test ./... -fuzz="^${func}$" -fuzztime=30s
-          done
+        run: make test-fuzz
 
-  mutation-test:
+  test-mutation:
     name: Mutation Tests
     runs-on: ubuntu-latest
     steps:
@@ -66,4 +100,4 @@ jobs:
         run: go install github.com/go-gremlins/gremlins/cmd/gremlins@latest
 
       - name: Run mutation tests
-        run: gremlins unleash
+        run: make test-mutation

.gitignore

@@ -24,4 +24,3 @@ go.work.sum
 
 # env file
 .env
-

.gremlins.yaml

@@ -4,4 +4,6 @@ unleash:
   timeout-coefficient: 50
   
   workers: 4
-  dry-run: false
+  dry-run: false
+  threshold:
+    efficacy: 1.0

.markdownlint.yml

@@ -0,0 +1,17 @@
+default: true
+heading-style:
+  style: atx
+ul-indent:
+  indent: 2
+line-length: false
+no-duplicate-heading:
+  siblings_only: true
+no-inline-html:
+  allowed_elements:
+    - br
+    - details
+    - summary
+    - img
+    - picture
+    - source
+first-line-heading: true

Makefile

@@ -1,12 +1,47 @@
-unit:
+.PHONY: all help install clean test-unit test-mutation test-fuzz test docs lint-go lint-makefile lint-markdown lint
+
+help: ## Show this help
+	@grep -E '^[a-zA-Z_-]+:.*##' $(MAKEFILE_LIST) | awk -F ':.*## ' '{printf "  %-15s %s\n", $$1, $$2}'
+
+install: ## Install dev tools
+	go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest
+	go install github.com/checkmake/checkmake/cmd/checkmake@latest
+	go install github.com/go-gremlins/gremlins/cmd/gremlins@latest
+	go install golang.org/x/tools/cmd/godoc@latest
+	go install golang.org/x/vuln/cmd/govulncheck@latest
+
+test-unit: ## Run unit tests with coverage
 	go test ./... -cover -v
 
-mutation:
+test-mutation: ## Run mutation tests with gremlins
 	gremlins unleash
 
-fuzz:
-	go test ./... -fuzz=$(FN)
+FUZZ_TIME ?= 30
 
-docs:
-	@echo ">>> Visit: http://localhost:6060/pkg/git.maximhutz.com/tools/dsa/"
-	godoc -http=:6060
+test-fuzz: ## Run all fuzz tests for 30s each
+	@for func in $$(grep -r --include='*_test.go' -oh 'func Fuzz\w*' . | sed 's/func //'); do \
+		echo "Fuzzing $$func..."; \
+		go test ./... -fuzz="^$$func$$" -fuzztime=$(FUZZ_TIME)s; \
+	done
+
+test: test-unit test-mutation test-fuzz ## Run all tests
+
+lint-go: ## Lint Go code
+	golangci-lint run ./...
+
+lint-makefile: ## Lint the Makefile
+	checkmake Makefile
+
+lint-markdown: ## Lint Markdown files
+	docker run --rm -v $(CURDIR):/workdir davidanson/markdownlint-cli2 "**/*.md"
+
+lint: lint-go lint-makefile lint-markdown ## Lint all code
+
+docs: ## Serve godoc locally
+	@echo ">>> Visit: http://localhost:6060/pkg/$$(go list -m)"
+	godoc -http=:6060
+
+clean: ## Clean build and test caches
+	go clean -cache -testcache
+
+all: lint test ## Run all checks and tests

README.md

@@ -1,3 +1,3 @@
-# go-cuckoo
+# <img height="30" src="assets/logo.svg" alt="Go Cuckoo, by `mvhutz`."> Go Cuckoo
 
-A hash table that uses cuckoo hashing to achieve a worst-case O(1) lookup time.
+A hash table that uses cuckoo hashing to achieve a worst-case O(1) lookup time. Read more about it in [the package documentation](https://pkg.go.dev/git.maximhutz.com/tools/go-cuckoo).

assets/logo.svg

@@ -0,0 +1 @@
+<svg width="16" height="16" xmlns="http://www.w3.org/2000/svg" shape-rendering="crispEdges"><path fill="#2a1512" d="M3,6h1v1h-1v-1M2,7h1v1h-1v-1M12,7h1v1h-1v-1M1,8h1v1h-1v-1M4,8h1v2h-1v-2M14,8h1v1h-1v-1M11,9h1v2h-2v-1h1v-1M5,10h1v1h-1v-1M1,13h2v1h1v1h-2v-1h-1v-1M13,13h2v1h-1v1h-1v1h-1v-2h1v-1M4,15h1v1h-1v-1"/><path fill="#38231f" d="M4,6h1v1h-1v-1M11,6h1v1h-1v-1M13,7h1v1h-1v-1M1,9h1v2h-1v-2M14,9h1v1h-1v-1M14,11h1v2h-1v-2M1,12h1v1h-1v-1M5,15h3v1h-3v-1M10,15h2v1h-2v-1"/><path fill="#3f3f74" d="M7,3h2v1h-2v-1M6,4h1v1h-1v-1M9,4h1v1h-1v-1M5,5h1v5h-1v-5M10,5h1v5h-1v-5M6,10h4v1h-4v-1"/><path fill="#6262ab" d="M9,5h1v1h-1v-1M6,9h1v1h-1v-1M9,9h1v1h-1v-1"/><path fill="#663931" d="M11,8h1v1h-1v-1M2,9h1v1h-1v-1M14,10h1v1h-1v-1M1,11h1v1h-1v-1M3,11h2v1h-2v-1M13,11h1v1h-1v-1M2,12h1v1h-1v-1M5,12h1v1h-1v-1M10,12h3v2h-1v-1h-2v-1M3,13h1v1h-1v-1M8,13h2v1h-2v-1M4,14h3v1h-3v-1M10,14h2v1h-2v-1M8,15h2v1h-2v-1"/><path fill="#8d8dcb" d="M9,6h1v3h-1v1h-2v-1h1v-1h1v-2M6,8h1v1h-1v-1"/><path fill="#8f563b" d="M2,8h1v1h-1v-1M12,9h1v1h-1v-1M2,10h1v1h-1v-1M13,10h1v1h-1v-1M7,11h1v1h-1v-1M11,11h2v1h-2v-1M4,12h1v1h1v-1h1v2h-3v-2M13,12h1v1h-1v-1M10,13h2v1h-2v-1M7,14h3v1h-3v-1"/><path fill="#a4a4d5" d="M8,4h1v4h-1v1h-1v-1h-1v-2h1v-1h1v-1"/><path fill="#ab764a" d="M4,7h1v1h-1v-1M3,8h1v2h-1v-2M12,10h1v1h-1v-1M2,11h1v1h-1v-1M8,11h1v1h-1v-1M3,12h1v1h-1v-1M7,12h1v2h-1v-2"/><path fill="#cacaea" d="M7,4h1v1h-1v-1M6,5h1v1h-1v-1"/><path fill="#d9a066" d="M3,7h1v1h-1v-1M11,7h1v1h-1v-1M12,8h2v2h-1v-1h-1v-1M3,10h2v1h-2v-1M5,11h2v1h-2v-1M9,11h2v1h-1v1h-2v-1h1v-1"/></svg>

bucket.go

@@ -1,12 +1,13 @@
 package cuckoo
 
-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
 }
 
@@ -17,48 +18,81 @@ type bucket[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.
 func (b bucket[K, V]) location(key K) uint64 {
 	return b.hash(key) % b.capacity
 }
 
 func (b bucket[K, V]) get(key K) (value V, found bool) {
+	if b.capacity == 0 {
+		return
+	}
+
 	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]) resize(capacity uint64) {
-	b.slots = make([]slot[K, V], capacity)
-	b.capacity = capacity
-	b.size = 0
-}
+func (b *bucket[K, V]) drop(key K) (occupied bool) {
+	if b.capacity == 0 {
+		return
+	}
 
-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.occupied = false
+		b.size--
 		return true
 	}
 
 	return false
 }
 
-func (b *bucket[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
-	slot := &b.slots[b.location(insertion.key)]
+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) {
+	if b.capacity == 0 {
+		return
+	}
+
+	slot := &b.slots[b.location(key)]
+
+	if slot.occupied && b.compare(slot.Key, key) {
+		slot.Value = value
+		return true
+	}
+
+	return false
+}
+
+func (b *bucket[K, V]) insert(insertion Entry[K, V]) (evicted Entry[K, V], eviction bool) {
+	if b.capacity == 0 {
+		return insertion, true
+	}
+
+	slot := &b.slots[b.location(insertion.Key)]
 
 	if !slot.occupied {
-		slot.entry = insertion
+		slot.Entry = insertion
 		slot.occupied = true
 		b.size++
 		return
 	}
 
-	if b.compare(slot.key, insertion.key) {
-		slot.value = insertion.value
+	if b.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
 }
 

cuckoo_fuzz_test.go

@@ -1,11 +1,13 @@
 package cuckoo_test
 
 import (
-	"bytes"
-	"encoding/binary"
+	"fmt"
+	"maps"
+	"os"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	go_fuzz_utils "github.com/trailofbits/go-fuzz-utils"
 
 	"git.maximhutz.com/tools/go-cuckoo"
 )
@@ -19,31 +21,73 @@ func offsetHash(seed uint32) cuckoo.Hash[uint32] {
 	}
 }
 
+type fuzzStep struct {
+	drop       bool
+	key, value uint32
+}
+
+type fuzzScenario struct {
+	seedA, seedB           uint32
+	capacity, growthFactor uint8
+	steps                  []fuzzStep
+}
+
 func FuzzInsertLookup(f *testing.F) {
-	f.Fuzz(func(t *testing.T, data []byte, seedA, seedB uint32) {
+	f.Fuzz(func(t *testing.T, data []byte) {
+		var scenario fuzzScenario
 		assert := assert.New(t)
 
-		table := cuckoo.NewCustomTable[uint32, uint32](
-			offsetHash(seedA),
-			offsetHash(seedB),
-			func(a, b uint32) bool { return a == b },
-		)
-
-		if seedA == seedB {
+		if tp, err := go_fuzz_utils.NewTypeProvider(data); err != nil {
+			return
+		} else if err := tp.Fill(&scenario); err != nil {
 			return
 		}
 
-		r := bytes.NewReader(data)
-		var key, value uint32
-		for binary.Read(r, binary.LittleEndian, &key) == nil &&
-			binary.Read(r, binary.LittleEndian, &value) == nil {
+		seedA, seedB := scenario.seedA, scenario.seedB
+		growthFactor := max(2, int(scenario.growthFactor))
+		capacity := int(scenario.capacity)
 
-			err := table.Put(key, value)
-			assert.NoError(err)
+		// If they are the same number, the hashes will clash, always causing an
+		// error.
+		if seedA == seedB {
+			t.Skip()
+		}
 
-			found, err := table.Get(key)
-			assert.NoError(err)
-			assert.Equal(value, found)
+		fmt.Fprintf(os.Stderr, "seedA=%d seedB=%d capacity=%d growthFactor=%d\n",
+			seedA, seedB, capacity, growthFactor)
+
+		actual := cuckoo.NewCustomTable[uint32, uint32](
+			offsetHash(seedA),
+			offsetHash(seedB),
+			func(a, b uint32) bool { return a == b },
+			cuckoo.Capacity(capacity),
+			cuckoo.GrowthFactor(growthFactor),
+		)
+
+		expected := map[uint32]uint32{}
+
+		for _, step := range scenario.steps {
+			if step.drop {
+				ok := actual.Drop(step.key)
+				_, has := expected[step.key]
+				assert.Equal(ok, has)
+
+				delete(expected, step.key)
+
+				_, err := actual.Get(step.key)
+				assert.Error(err)
+			} else {
+				_, err := actual.Put(step.key, step.value)
+				assert.NoError(err)
+
+				expected[step.key] = step.value
+
+				found, err := actual.Get(step.key)
+				assert.NoError(err)
+				assert.Equal(step.value, found)
+			}
+
+			assert.Equal(expected, maps.Collect(actual.Entries()))
 		}
 	})
 }

cuckoo_internal_test.go

@@ -23,8 +23,8 @@ 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.Capacity()), table.load())
+		assert.Equal(float64(table.Size())/float64(table.TotalCapacity()), table.load())
 	}
 }

cuckoo_test.go

@@ -1,6 +1,7 @@
 package cuckoo_test
 
 import (
+	"errors"
 	"maps"
 	"math/rand/v2"
 	"testing"
@@ -24,7 +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())
@@ -37,7 +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())
@@ -51,9 +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)
@@ -64,7 +65,7 @@ func TestStartingCapacity(t *testing.T) {
 	assert := assert.New(t)
 	table := cuckoo.NewTable[int, bool](cuckoo.Capacity(64))
 
-	assert.Equal(uint64(128), table.Capacity())
+	assert.Equal(uint64(128), table.TotalCapacity())
 }
 
 func TestResizeCapacity(t *testing.T) {
@@ -74,12 +75,12 @@ func TestResizeCapacity(t *testing.T) {
 		cuckoo.GrowthFactor(2),
 	)
 
-	for table.Capacity() == 16 {
-		err := table.Put(rand.Int(), true)
+	for table.TotalCapacity() == 16 {
+		_, err := table.Put(rand.Int(), true)
 		assert.NoError(err)
 	}
 
-	assert.Equal(uint64(32), table.Capacity())
+	assert.Equal(uint64(32), table.TotalCapacity())
 }
 
 func TestPutMany(t *testing.T) {
@@ -88,7 +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)
 	}
@@ -102,7 +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)
 	}
 
@@ -117,14 +118,111 @@ func TestGetMany(t *testing.T) {
 	}
 }
 
-func TestRemove(t *testing.T) {
+func TestDropExistingItem(t *testing.T) {
 	assert := assert.New(t)
+	key, value := 0, true
+	table := cuckoo.NewTable[int, bool]()
+	(table.Put(key, value))
+
+	had := table.Drop(key)
+
+	assert.True(had)
+	assert.Equal(0, table.Size())
+	assert.False(table.Has(key))
+}
+
+func TestDropNoItem(t *testing.T) {
+	assert := assert.New(t)
+	key := 0
 	table := cuckoo.NewTable[int, bool]()
 
-	assert.False(table.Has(0))
+	had := table.Drop(key)
 
-	err := table.Put(0, true)
-	assert.NoError(err)
-
-	assert.True(table.Has(0))
+	assert.False(had)
+	assert.Equal(0, table.Size())
+	assert.False(table.Has(key))
+}
+
+func TestDropItemCapacity(t *testing.T) {
+	assert := assert.New(t)
+	key := 0
+	table := cuckoo.NewTable[int, bool](
+		cuckoo.Capacity(64),
+		cuckoo.GrowthFactor(2),
+	)
+
+	startingCapacity := table.TotalCapacity()
+	table.Drop(key)
+	endingCapacity := table.TotalCapacity()
+
+	assert.Equal(0, table.Size())
+	assert.Equal(uint64(128), startingCapacity)
+	assert.Equal(uint64(64), endingCapacity)
+}
+
+func TestPutNoCapacity(t *testing.T) {
+	assert := assert.New(t)
+	key, value := 0, true
+	table := cuckoo.NewTable[int, bool](
+		cuckoo.Capacity(0),
+	)
+
+	_, err := table.Put(key, value)
+
+	assert.NoError(err)
+	assert.Equal(1, table.Size())
+	assert.True(table.Has(key))
+}
+
+func TestBadHashCapacity(t *testing.T) {
+	assert := assert.New(t)
+	table := cuckoo.NewCustomTable[int, bool](
+		func(int) uint64 { return 0 },
+		func(int) uint64 { return 0 },
+		func(a, b int) bool { return a == b },
+		cuckoo.Capacity(20),
+	)
+
+	_, err1 := table.Put(0, true)
+	_, err2 := table.Put(1, true)
+	_, err3 := table.Put(2, true)
+
+	assert.NoError(err1)
+	assert.NoError(err2)
+	assert.Error(err3)
+
+	assert.Equal(uint64(80), table.TotalCapacity())
+}
+
+func TestDropResizeCapacity(t *testing.T) {
+	assert := assert.New(t)
+	table := cuckoo.NewTable[int, bool](
+		cuckoo.Capacity(10),
+	)
+
+	_, err1 := table.Put(0, true)
+	_, err2 := table.Put(1, true)
+	table.Drop(1)
+
+	assert.NoError(errors.Join(err1, err2))
+	assert.Equal(uint64(20), table.TotalCapacity())
+}
+
+func TestNewTableBy(t *testing.T) {
+	type User struct {
+		_    func()
+		id   string
+		name string
+	}
+
+	assert := assert.New(t)
+	table := cuckoo.NewTableBy[User, bool](
+		func(u User) string { return u.id },
+	)
+
+	_, err := table.Put(User{nil, "1", "Robert"}, true)
+
+	assert.NoError(err)
+	assert.Equal(1, table.Size())
+	assert.True(table.Has(User{nil, "1", "Robbie"}))
 }

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)
 	}
 

go.mod

@@ -4,8 +4,11 @@ go 1.25.6
 
 require github.com/stretchr/testify v1.11.1
 
+require github.com/kr/pretty v0.3.1 // indirect
+
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/trailofbits/go-fuzz-utils v0.0.0-20260318143407-0907cafe7589
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,10 +1,21 @@
+github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
+github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
+github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+github.com/trailofbits/go-fuzz-utils v0.0.0-20260318143407-0907cafe7589 h1:UmBZCTPdDYore2IEHN+U4eIqEaRq6METh9pKiPumkqc=
+github.com/trailofbits/go-fuzz-utils v0.0.0-20260318143407-0907cafe7589/go.mod h1:zh+T+w9XT/3o4E0WLEGCdmLJ8Yqx/zY3o538tQY3OjY=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

settings.go

@@ -1,5 +1,7 @@
 package cuckoo
 
+import "fmt"
+
 // DefaultCapacity is the initial capacity of a [Table]. It is inspired from
 // Java's [HashMap] implementation, which also uses 16.
 //
@@ -10,11 +12,17 @@ const DefaultCapacity uint64 = 16
 // hash table implementations use 2.
 const DefaultGrowthFactor uint64 = 2
 
-// DefaultMinimumLoad is the default lowest acceptable occupancy of a [Table].
-// The value of 5% is taken from [libcuckoo].
+// defaultMinimumLoad is the default lowest acceptable occupancy of a [Table].
+// The higher the minimum load, the more likely that a [Table.Put] will not
+// succeed. The value of 5% is taken from [libcuckoo].
 //
 // [libcuckoo]: https://github.com/efficient/libcuckoo/blob/656714705a055df2b7a605eb3c71586d9da1e119/libcuckoo/cuckoohash_config.hh#L21
-const DefaultMinimumLoad float64 = 0.05
+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
@@ -27,19 +35,21 @@ type settings struct {
 type Option func(*settings)
 
 // Capacity modifies the starting capacity of each bucket of the [Table]. The
-// value must be greater than 0.
+// value must be non-negative.
 func Capacity(value int) Option {
-	return func(s *settings) { s.bucketSize = uint64(value) }
-}
+	if value < 0 {
+		panic(fmt.Sprintf("go-cuckoo: Capacity must be non-negative, got %d", value))
+	}
 
-// MinimumLoad modifies the [DefaultMinimumLoad] of the [Table]. The value must
-// be between 0.00 and 1.00.
-func MinimumLoad(value float64) Option {
-	return func(s *settings) { s.minLoadFactor = value }
+	return func(s *settings) { s.bucketSize = uint64(value) }
 }
 
 // GrowthFactor controls how much the capacity of the [Table] multiplies when
 // it must resize. The value must be greater than 1.
 func GrowthFactor(value int) Option {
+	if value < 2 {
+		panic(fmt.Sprintf("go-cuckoo: GrowthFactor must be greater than 1, got %d", value))
+	}
+
 	return func(s *settings) { s.growthFactor = uint64(value) }
 }

table.go

@@ -16,9 +16,9 @@ type Table[K, V any] struct {
 	minLoadFactor    float64
 }
 
-// Capacity returns the number of slots allocated for the [Table]. To get the
+// TotalCapacity returns the number of slots allocated for the [Table]. To get the
 // number of slots filled, look at [Table.Size].
-func (t Table[K, V]) Capacity() uint64 {
+func (t Table[K, V]) TotalCapacity() uint64 {
 	return t.bucketA.capacity + t.bucketB.capacity
 }
 
@@ -28,33 +28,93 @@ func (t Table[K, V]) Size() int {
 }
 
 func log2(n uint64) (m int) {
-	return bits.Len64(n) - 1
+	return max(0, bits.Len64(n)-1)
 }
 
 func (t Table[K, V]) maxEvictions() int {
-	return 3 * log2(t.Capacity())
+	return 3 * log2(t.TotalCapacity())
 }
 
 func (t Table[K, V]) load() float64 {
-	return float64(t.Size()) / float64(t.Capacity())
-}
-
-func (t *Table[K, V]) resize() error {
-	entries := make([]entry[K, V], 0, t.Size())
-	for k, v := range t.Entries() {
-		entries = append(entries, entry[K, V]{k, v})
+	// When there are no slots in the table, we still treat the load as 100%.
+	// Every slot in the table is full.
+	if t.TotalCapacity() == 0 {
+		return 1.0
 	}
 
-	t.bucketA.resize(t.growthFactor * t.bucketA.capacity)
-	t.bucketB.resize(t.growthFactor * t.bucketB.capacity)
+	return float64(t.Size()) / float64(t.TotalCapacity())
+}
 
-	for _, entry := range entries {
-		if err := t.Put(entry.key, entry.value); err != nil {
-			return err
+// 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
+	}
+
+	if t.bucketB.update(entry.Key, entry.Value) {
+		return
+	}
+
+	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() bool {
+	var newCapacity uint64
+
+	if t.TotalCapacity() == 0 {
+		newCapacity = 1
+	} else {
+		newCapacity = t.bucketA.capacity * t.growthFactor
+	}
+
+	return t.resize(newCapacity)
+}
+
+// shrink reduces the table's capacity by the [Table.growthFactor]. It may
+// reduce it down to 0.
+func (t *Table[K, V]) shrink() bool {
+	return t.resize(t.bucketA.capacity / t.growthFactor)
 }
 
 // Get fetches the value for a key in the [Table]. Returns an error if no value
@@ -77,44 +137,52 @@ 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.Capacity(), t.load())
-	}
-
-	if err := t.resize(); 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
-// cannot be removed.
-//
-// Deprecated: Do not use.
-func (t Table[K, V]) Drop(_ K) {
-	panic("Not implemented")
+// 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
+		// optimization.
+		t.shrink()
+	}
+
+	return occupied
 }
 
 // Entries returns an unordered sequence of all key-value pairs in the table.
@@ -122,7 +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
 				}
 			}
@@ -130,7 +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
 				}
 			}
@@ -164,7 +232,7 @@ func NewCustomTable[K, V any](hashA, hashB Hash[K], compare EqualFunc[K], option
 	settings := &settings{
 		growthFactor:  DefaultGrowthFactor,
 		bucketSize:    DefaultCapacity,
-		minLoadFactor: DefaultMinimumLoad,
+		minLoadFactor: defaultMinimumLoad,
 	}
 
 	for _, option := range options {