14 Commits

Author SHA1 Message Date
6a5b40c097 docs: replaced instances of "bucket" with "table"
- Removed instances of `growthFactor`, as it is unexported.
- Typo in `HashTable.String()`.
2026-04-13 20:49:33 -04:00
395a3560c7 refactor: constructors, update docs
- NewCustomTable -> NewCustom
- NewTableBy -> NewBy
- NewTable -> New
2026-04-04 12:27:53 +02:00
2fd9da973b refactor: bucket -> table, Table -> HashTable 2026-04-04 12:22:42 +02:00
322d71f0be refactor!: remove MinimumLoad() option (#17)
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## 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
2026-04-03 14:51:41 +00:00
ed30a4fc7c fix: check-pr-title job has prompt injection (#18)
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## Description

Currently, the `check-pr-title` job has a security vulnerability. If you give the PR a bad title, the job can run arbitrary code.

## Changes

- Fix prompt injection by pulling the PR title as an environment variable.
- Also, restricted the job to only `pull_request` trigger.

### Design Decisions

- It is better to pull out this job into a separate workflow with a unique trigger, but I chose not to because it is currently only one job.

## Checklist

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

Reviewed-on: #18
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-04-03 14:47:01 +00:00
c834f004a2 chore: no free form issues, 'description'-s to 'placeholders'-s (#16)
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## Description

There were some problems with the roll-out of the issue templates. This PR addresses them.

## Changes

- Disable `blank-issue-enabled`.
- Move all `description` types in the issue templates to `placeholder`.

### Design Decisions

- The `description` fields take up too much space.

## Checklist

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

Reviewed-on: #16
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-04-03 13:57:03 +00:00
581f26f562 ci: support semantic versioning, conventional commits (#15)
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## Description

Currently, the repository is not well suited for semantic versioning, and hasn't much to support it. This PR adds templates, CI jobs, and configs to simplify its adoption.

## Changes

- Added `FEATURE` and `BUG` issue templates. Also, forbids free-form issues.
- Adds a PR template.
- Adds a CI job to ensure the commit title follows conventional commits.

### Design Decisions

N/A.

## Checklist

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

Reviewed-on: #15
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-04-03 13:46:05 +00:00
b1ab3a6326 chore: remove ./.claude/settings.json (#14)
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There shouldn't be a global settings folder for Claude in the repository. Also, add final newline to `.gitignore`.

Reviewed-on: #14
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-28 19:52:06 +00:00
36d76d4929 feat: wider fuzz tests, stronger options. (#9)
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- Added all `Option`-s to the fuzz tests.
  - Minimum load is always <=20%.
- Tested all options, and force a panic on all invalid options.
  - Capacity must now be non-negative.
  - Minimum load should be <=20%, but just put it as a recommendation.

Reviewed-on: #9
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-25 01:26:56 +00:00
41b09ae680 fix: remove redundant test TestRemove (#8)
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This test offers the same functionality as `TestAddItem`.

Reviewed-on: #8
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-21 16:24:52 +00:00
e00e6fcb1b docs: add logo for project, expand readme (#7)
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Reviewed-on: #7
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-21 01:14:17 +00:00
56b1982f8a feat: add drop key functionality (#6)
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Currently, the `Table.Drop()` function is deprecated because it is not implemented yet. Let's add that functionality.

- Adds true drop functionality to the table, through `Table.Drop()`.
- Adds tests for functionality.
- Rewrites fuzz test using `go_fuzz_utils`, to test arbitrary usage patterns.
- Rewrite `bucket` to allow a capacity of zero.
- Rename `Table.Capacity()` to `Table.TotalCapacity()`, to reflect to different between the capacity of the buckets vs. the whole table.
- Enforce 100% mutation test coverage.

Reviewed-on: #6
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-20 01:59:54 +00:00
2bfaede2d4 ci: add lint makefile job (#5)
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Currently, there is no CI job to lint the Makefile. This adds one.

Reviewed-on: #5
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-19 00:24:25 +00:00
ece10585a5 style: restructure makefile (#4)
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Currently, the `Makefile` is not well structured, and does not follow best practices. With the help of [`checkmake`](https://github.com/checkmake/checkmake), the Makefile can be forced to follow them.

### Decisions

- Added CI job `lint-makefile`, which forces the Makefile to conform to standards.
- The `make help` was set as the default target. This is common practice in the industry.
- The `make help` uses `grep` | `awk` to create a command table from `##` comments after each target. It seems a bit icky, but it is something that Docker, Kubernetes, and Helm all do.

Reviewed-on: #4
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-19 00:14:54 +00:00
27 changed files with 720 additions and 327 deletions

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@@ -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

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@@ -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.

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

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

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@@ -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

1
.gitignore vendored
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@@ -24,4 +24,3 @@ go.work.sum
# env file
.env

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@@ -5,3 +5,5 @@ unleash:
workers: 4
dry-run: false
threshold:
efficacy: 1.0

17
.markdownlint.yml Normal file
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@@ -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

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@@ -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/"
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

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@@ -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).

1
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@@ -0,0 +1 @@
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@@ -1,73 +0,0 @@
package cuckoo
type entry[K, V any] struct {
key K
value V
}
type slot[K, V any] struct {
entry[K, V]
occupied bool
}
type bucket[K, V any] struct {
hash Hash[K]
slots []slot[K, V]
capacity, size uint64
compare EqualFunc[K]
}
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) {
slot := b.slots[b.location(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]) update(key K, value V) (updated bool) {
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]) evict(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
slot := &b.slots[b.location(insertion.key)]
if !slot.occupied {
slot.entry = insertion
slot.occupied = true
b.size++
return
}
if b.compare(slot.key, insertion.key) {
slot.value = insertion.value
return
}
insertion, slot.entry = slot.entry, insertion
return insertion, true
}
func newBucket[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) bucket[K, V] {
return bucket[K, V]{
hash: hash,
capacity: capacity,
compare: compare,
size: 0,
slots: make([]slot[K, V], capacity),
}
}

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@@ -1,11 +1,11 @@
package cuckoo
// An EqualFunc determines whethers two keys are 'equal'. Keys that are 'equal'
// are teated as the same by the [Table]. A good EqualFunc is pure,
// deterministic, and fast. By default, [NewTable] uses [DefaultEqualFunc].
// are teated as the same by the [HashTable]. A good EqualFunc is pure,
// deterministic, and fast. By default, [New] uses [DefaultEqualFunc].
//
// This function MUST NOT return true if the [Hash] digest of two keys
// are different: the [Table] will not work.
// are different: the [HashTable] will not work.
type EqualFunc[K any] = func(a, b K) bool
// DefaultEqualFunc compares two keys by strict equality. Returns true if the

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@@ -28,7 +28,7 @@ func ExampleEqualFunc_badEqualFunc() {
// Two users with the same ID are equal.
isEqual := func(a, b User) bool { return a.ID == b.ID }
userbase := cuckoo.NewCustomTable[User, bool](makeHash(1), makeHash(2), isEqual)
userbase := cuckoo.NewCustom[User, bool](makeHash(1), makeHash(2), isEqual)
(userbase.Put(User{"1", "Robert Doe"}, true))

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@@ -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 +21,72 @@ 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)
// If they are the same number, the hashes will clash, always causing an
// error.
if seedA == seedB {
t.Skip()
}
fmt.Fprintf(os.Stderr, "seedA=%d seedB=%d capacity=%d growthFactor=%d\n",
seedA, seedB, capacity, growthFactor)
actual := cuckoo.NewCustom[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 {
err := actual.Drop(step.key)
assert.NoError(err)
found, err := table.Get(key)
delete(expected, step.key)
_, err = actual.Get(step.key)
assert.Error(err)
} else {
err := actual.Put(step.key, step.value)
assert.NoError(err)
assert.Equal(value, found)
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()))
}
})
}

View File

@@ -11,7 +11,7 @@ func TestMaxEvictions(t *testing.T) {
assert := assert.New(t)
for i := 16; i < 116; i++ {
table := NewTable[int, bool](Capacity(i / 2))
table := New[int, bool](Capacity(i / 2))
expectedEvictions := 3 * math.Floor(math.Log2(float64(i)))
assert.Equal(table.maxEvictions(), int(expectedEvictions))
@@ -20,11 +20,11 @@ func TestMaxEvictions(t *testing.T) {
func TestLoad(t *testing.T) {
assert := assert.New(t)
table := NewTable[int, bool](Capacity(8))
table := New[int, bool](Capacity(8))
for i := range 16 {
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())
}
}

View File

@@ -1,6 +1,7 @@
package cuckoo_test
import (
"errors"
"maps"
"math/rand/v2"
"testing"
@@ -13,7 +14,7 @@ import (
func TestNewTable(t *testing.T) {
assert := assert.New(t)
table := cuckoo.NewTable[int, bool]()
table := cuckoo.New[int, bool]()
assert.NotNil(table)
assert.Zero(table.Size())
@@ -22,7 +23,7 @@ func TestNewTable(t *testing.T) {
func TestAddItem(t *testing.T) {
assert := assert.New(t)
key, value := 0, true
table := cuckoo.NewTable[int, bool]()
table := cuckoo.New[int, bool]()
err := table.Put(key, value)
@@ -34,7 +35,7 @@ func TestAddItem(t *testing.T) {
func TestPutOverwrite(t *testing.T) {
assert := assert.New(t)
key, value, newValue := 0, 1, 2
table := cuckoo.NewTable[int, int]()
table := cuckoo.New[int, int]()
(table.Put(key, value))
err := table.Put(key, newValue)
@@ -49,7 +50,7 @@ func TestPutOverwrite(t *testing.T) {
func TestSameHash(t *testing.T) {
assert := assert.New(t)
hash := func(int) uint64 { return 0 }
table := cuckoo.NewCustomTable[int, bool](hash, hash, cuckoo.DefaultEqualFunc[int])
table := cuckoo.NewCustom[int, bool](hash, hash, cuckoo.DefaultEqualFunc[int])
errA := table.Put(0, true)
errB := table.Put(1, true)
@@ -62,29 +63,29 @@ func TestSameHash(t *testing.T) {
func TestStartingCapacity(t *testing.T) {
assert := assert.New(t)
table := cuckoo.NewTable[int, bool](cuckoo.Capacity(64))
table := cuckoo.New[int, bool](cuckoo.Capacity(64))
assert.Equal(uint64(128), table.Capacity())
assert.Equal(uint64(128), table.TotalCapacity())
}
func TestResizeCapacity(t *testing.T) {
assert := assert.New(t)
table := cuckoo.NewTable[int, bool](
table := cuckoo.New[int, bool](
cuckoo.Capacity(8),
cuckoo.GrowthFactor(2),
)
for table.Capacity() == 16 {
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) {
assert := assert.New(t)
expected, actual := map[int]bool{}, cuckoo.NewTable[int, bool]()
expected, actual := map[int]bool{}, cuckoo.New[int, bool]()
for i := range 1_000 {
expected[i] = true
@@ -99,7 +100,7 @@ func TestPutMany(t *testing.T) {
func TestGetMany(t *testing.T) {
assert := assert.New(t)
table := cuckoo.NewTable[int, bool]()
table := cuckoo.New[int, bool]()
for i := range 1_000 {
err := table.Put(i, true)
@@ -117,14 +118,110 @@ func TestGetMany(t *testing.T) {
}
}
func TestRemove(t *testing.T) {
func TestDropExistingItem(t *testing.T) {
assert := assert.New(t)
table := cuckoo.NewTable[int, bool]()
key, value := 0, true
table := cuckoo.New[int, bool]()
(table.Put(key, value))
assert.False(table.Has(0))
err := table.Drop(key)
err := table.Put(0, true)
assert.NoError(err)
assert.True(table.Has(0))
assert.Equal(0, table.Size())
assert.False(table.Has(key))
}
func TestDropNoItem(t *testing.T) {
assert := assert.New(t)
key := 0
table := cuckoo.New[int, bool]()
err := table.Drop(key)
assert.NoError(err)
assert.Equal(0, table.Size())
assert.False(table.Has(key))
}
func TestDropItemCapacity(t *testing.T) {
assert := assert.New(t)
key := 0
table := cuckoo.New[int, bool](
cuckoo.Capacity(64),
cuckoo.GrowthFactor(2),
)
startingCapacity := table.TotalCapacity()
err := table.Drop(key)
endingCapacity := table.TotalCapacity()
assert.NoError(err)
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.New[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.NewCustom[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.New[int, bool](
cuckoo.Capacity(10),
)
err1 := table.Put(0, true)
err2 := table.Put(1, true)
err3 := table.Drop(1)
assert.NoError(errors.Join(err1, err2, err3))
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.NewBy[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"}))
}

4
doc.go
View File

@@ -1,8 +1,8 @@
// Package cuckoo provides a hash table that uses cuckoo hashing to achieve
// a worst-case O(1) lookup time.
//
// While a [NewTable] only supports comparable keys by default, you can create
// a table with any key type using [NewCustomTable]. Custom [Hash] functions and
// While a [New] only supports comparable keys by default, you can create
// a table with any key type using [NewCustom]. Custom [Hash] functions and
// key comparison are also supported.
//
// See more: https://en.wikipedia.org/wiki/Cuckoo_hashing

View File

@@ -8,7 +8,7 @@ import (
)
func Example_basic() {
table := cuckoo.NewTable[int, string]()
table := cuckoo.New[int, string]()
if err := table.Put(1, "Hello, World!"); err != nil {
fmt.Println("Put error:", err)

3
go.mod
View File

@@ -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
)

13
go.sum
View File

@@ -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=

View File

@@ -7,9 +7,9 @@ import (
// A Hash function maps any data to a fixed-length value (in this case, a
// [uint64]).
//
// It is used by the [Table] to evenly distribute values
// It is used by the [HashTable] to evenly distribute values
// amongst its slots. A good hash function is uniform, [chaotic], and
// deterministic. [Table] uses [NewDefaultHash] by default, which is built on
// deterministic. [HashTable] uses [NewDefaultHash] by default, which is built on
// [maphash.Comparable].
//
// [chaotic]: https://en.wikipedia.org/wiki/Avalanche_effect

237
hash_table.go Normal file
View File

@@ -0,0 +1,237 @@
package cuckoo
import (
"fmt"
"iter"
"math/bits"
"strings"
)
// A HashTable which uses cuckoo hashing to resolve collision. Create
// one with [New]. Or if you want more granularity, use [NewBy] or
// [NewCustom].
type HashTable[K, V any] struct {
tableA, tableB table[K, V]
growthFactor uint64
minLoadFactor float64
}
// TotalCapacity returns the number of slots allocated for the [HashTable]. To get the
// number of slots filled, look at [HashTable.Size].
func (t *HashTable[K, V]) TotalCapacity() uint64 {
return t.tableA.capacity + t.tableB.capacity
}
// Size returns how many slots are filled in the [HashTable].
func (t *HashTable[K, V]) Size() int {
return int(t.tableA.size + t.tableB.size)
}
func log2(n uint64) (m int) {
return max(0, bits.Len64(n)-1)
}
func (t *HashTable[K, V]) maxEvictions() int {
return 3 * log2(t.TotalCapacity())
}
func (t *HashTable[K, V]) load() float64 {
// 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
}
return float64(t.Size()) / float64(t.TotalCapacity())
}
// resize clears all tables, changes the sizes of them to a specific capacity,
// and fills them back up again. It is a helper function for [HashTable.grow] and
// [HashTable.shrink]; use them instead.
func (t *HashTable[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})
}
t.tableA.resize(capacity)
t.tableB.resize(capacity)
for _, entry := range entries {
if err := t.Put(entry.key, entry.value); err != nil {
return err
}
}
return nil
}
// grow increases the table's capacity by the growth factor. If the
// capacity is 0, it increases it to 1.
func (t *HashTable[K, V]) grow() error {
var newCapacity uint64
if t.TotalCapacity() == 0 {
newCapacity = 1
} else {
newCapacity = t.tableA.capacity * t.growthFactor
}
return t.resize(newCapacity)
}
// shrink reduces the table's capacity by the growth factor. It may
// reduce it down to 0.
func (t *HashTable[K, V]) shrink() error {
return t.resize(t.tableA.capacity / t.growthFactor)
}
// Get fetches the value for a key in the [HashTable]. Returns an error if no value
// is found.
func (t *HashTable[K, V]) Get(key K) (value V, err error) {
if item, ok := t.tableA.get(key); ok {
return item, nil
}
if item, ok := t.tableB.get(key); ok {
return item, nil
}
return value, fmt.Errorf("key '%v' not found", key)
}
// Has returns true if a key has a value in the table.
func (t *HashTable[K, V]) Has(key K) (exists bool) {
_, err := t.Get(key)
return err == nil
}
// Put sets the value for a key. Returns error if its value cannot be set.
func (t *HashTable[K, V]) Put(key K, value V) (err error) {
if t.tableA.update(key, value) {
return nil
}
if t.tableB.update(key, value) {
return nil
}
entry, eviction := entry[K, V]{key, value}, false
for range t.maxEvictions() {
if entry, eviction = t.tableA.evict(entry); !eviction {
return nil
}
if entry, eviction = t.tableB.evict(entry); !eviction {
return nil
}
}
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)
}
// Drop removes a value for a key in the table. Returns an error if its value
// cannot be removed.
func (t *HashTable[K, V]) Drop(key K) (err error) {
t.tableA.drop(key)
t.tableB.drop(key)
if t.load() < t.minLoadFactor {
return t.shrink()
}
return nil
}
// Entries returns an unordered sequence of all key-value pairs in the table.
func (t *HashTable[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) {
return
}
}
}
for _, slot := range t.tableB.slots {
if slot.occupied {
if !yield(slot.key, slot.value) {
return
}
}
}
}
}
// String returns the entries of the table as a string in the format:
// "table[k1:v1 k2:v2 ...]".
func (t *HashTable[K, V]) String() string {
var sb strings.Builder
sb.WriteString("table[")
first := true
for k, v := range t.Entries() {
if !first {
sb.WriteString(" ")
}
fmt.Fprintf(&sb, "%v:%v", k, v)
first = false
}
sb.WriteString("]")
return sb.String()
}
// NewCustom creates a [HashTable] with custom [Hash] and [EqualFunc]
// functions, along with any [Option] the user provides.
func NewCustom[K, V any](hashA, hashB Hash[K], compare EqualFunc[K], options ...Option) *HashTable[K, V] {
settings := &settings{
growthFactor: DefaultGrowthFactor,
bucketSize: DefaultCapacity,
minLoadFactor: defaultMinimumLoad,
}
for _, option := range options {
option(settings)
}
return &HashTable[K, V]{
growthFactor: settings.growthFactor,
minLoadFactor: settings.minLoadFactor,
tableA: newTable[K, V](settings.bucketSize, hashA, compare),
tableB: newTable[K, V](settings.bucketSize, hashB, compare),
}
}
func pipe[X, Y, Z any](a func(X) Y, b func(Y) Z) func(X) Z {
return func(x X) Z { return b(a(x)) }
}
// NewBy creates a [HashTable] for any key type by using keyFunc to derive a
// comparable key. Two keys with the same derived key are treated as equal.
func NewBy[K, V any, C comparable](keyFunc func(K) C, options ...Option) *HashTable[K, V] {
return NewCustom[K, V](
pipe(keyFunc, NewDefaultHash[C]()),
pipe(keyFunc, NewDefaultHash[C]()),
func(a, b K) bool { return keyFunc(a) == keyFunc(b) },
options...,
)
}
// New creates a [HashTable] using the default [Hash] and [EqualFunc]. Use
// the [Option] functions to configure its behavior. Note that this constructor
// is only provided for comparable keys. For arbitrary keys, consider
// [NewBy] or [NewCustom].
func New[K comparable, V any](options ...Option) *HashTable[K, V] {
return NewCustom[K, V](NewDefaultHash[K](), NewDefaultHash[K](), DefaultEqualFunc[K], options...)
}

View File

@@ -1,20 +1,23 @@
package cuckoo
// DefaultCapacity is the initial capacity of a [Table]. It is inspired from
import "fmt"
// DefaultCapacity is the initial capacity of a [HashTable]. It is inspired from
// Java's [HashMap] implementation, which also uses 16.
//
// [HashMap]: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#HashMap--
const DefaultCapacity uint64 = 16
// DefaultGrowthFactor is the standard resize multiplier for a [Table]. Most
// hash table implementations use 2.
// DefaultGrowthFactor is the standard resize multiplier for a [HashTable]. Most
// 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 [HashTable].
// The higher the minimum load, the more likely that a [HashTable.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
type settings struct {
growthFactor uint64
@@ -22,24 +25,26 @@ type settings struct {
bucketSize uint64
}
// An Option modifies the settings of a [Table]. It is used in its constructors
// like [NewTable], for example.
// An Option modifies the settings of a [HashTable]. It is used in its constructors
// like [New], for example.
type Option func(*settings)
// Capacity modifies the starting capacity of each bucket of the [Table]. The
// value must be greater than 0.
// Capacity modifies the starting capacity of each table of the [HashTable]. The
// value must be non-negative.
func Capacity(value int) Option {
if value < 0 {
panic(fmt.Sprintf("go-cuckoo: Capacity must be non-negative, got %d", value))
}
return func(s *settings) { s.bucketSize = uint64(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 }
}
// GrowthFactor controls how much the capacity of the [Table] multiplies when
// GrowthFactor controls how much the capacity of the [HashTable] 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) }
}

254
table.go
View File

@@ -1,203 +1,103 @@
package cuckoo
import (
"fmt"
"iter"
"math/bits"
"strings"
)
// A Table is hash table that uses cuckoo hashing to resolve collision. Create
// one with [NewTable]. Or if you want more granularity, use [NewTableBy] or
// [NewCustomTable].
type Table[K, V any] struct {
bucketA, bucketB bucket[K, V]
growthFactor uint64
minLoadFactor float64
type entry[K, V any] struct {
key K
value V
}
// Capacity 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 {
return t.bucketA.capacity + t.bucketB.capacity
type slot[K, V any] struct {
entry[K, V]
occupied bool
}
// Size returns how many slots are filled in the [Table].
func (t Table[K, V]) Size() int {
return int(t.bucketA.size + t.bucketB.size)
type table[K, V any] struct {
hash Hash[K]
slots []slot[K, V]
capacity, size uint64
compare EqualFunc[K]
}
func log2(n uint64) (m int) {
return bits.Len64(n) - 1
// location determines where in the table a certain key would be placed. If the
// capacity is 0, this will panic.
func (t table[K, V]) location(key K) uint64 {
return t.hash(key) % t.capacity
}
func (t Table[K, V]) maxEvictions() int {
return 3 * log2(t.Capacity())
}
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})
}
t.bucketA.resize(t.growthFactor * t.bucketA.capacity)
t.bucketB.resize(t.growthFactor * t.bucketB.capacity)
for _, entry := range entries {
if err := t.Put(entry.key, entry.value); err != nil {
return err
}
}
return nil
}
// Get fetches the value for a key in the [Table]. Returns an error if no value
// is found.
func (t Table[K, V]) Get(key K) (value V, err error) {
if item, ok := t.bucketA.get(key); ok {
return item, nil
}
if item, ok := t.bucketB.get(key); ok {
return item, nil
}
return value, fmt.Errorf("key '%v' not found", key)
}
// Has returns true if a key has a value in the table.
func (t Table[K, V]) Has(key K) (exists bool) {
_, err := t.Get(key)
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
}
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
}
if entry, eviction = t.bucketB.evict(entry); !eviction {
return nil
}
}
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)
}
// 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")
}
// Entries returns an unordered sequence of all key-value pairs in the table.
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) {
func (t table[K, V]) get(key K) (value V, found bool) {
if t.capacity == 0 {
return
}
}
}
for _, slot := range t.bucketB.slots {
if slot.occupied {
if !yield(slot.key, slot.value) {
slot := t.slots[t.location(key)]
return slot.value, slot.occupied && t.compare(slot.key, key)
}
func (t *table[K, V]) drop(key K) (occupied bool) {
if t.capacity == 0 {
return
}
slot := &t.slots[t.location(key)]
if slot.occupied && t.compare(slot.key, key) {
slot.occupied = false
t.size--
return true
}
}
}
return false
}
// String returns the entries of the table as a string in the format:
// "table[k1:v1 h2:v2 ...]".
func (t Table[K, V]) String() string {
var sb strings.Builder
sb.WriteString("table[")
first := true
for k, v := range t.Entries() {
if !first {
sb.WriteString(" ")
}
fmt.Fprintf(&sb, "%v:%v", k, v)
first = false
}
sb.WriteString("]")
return sb.String()
func (t *table[K, V]) resize(capacity uint64) {
t.slots = make([]slot[K, V], capacity)
t.capacity = capacity
t.size = 0
}
// NewCustomTable creates a [Table] with custom [Hash] and [EqualFunc]
// functions, along with any [Option] the user provides.
func NewCustomTable[K, V any](hashA, hashB Hash[K], compare EqualFunc[K], options ...Option) *Table[K, V] {
settings := &settings{
growthFactor: DefaultGrowthFactor,
bucketSize: DefaultCapacity,
minLoadFactor: DefaultMinimumLoad,
func (t table[K, V]) update(key K, value V) (updated bool) {
if t.capacity == 0 {
return
}
for _, option := range options {
option(settings)
slot := &t.slots[t.location(key)]
if slot.occupied && t.compare(slot.key, key) {
slot.value = value
return true
}
return &Table[K, V]{
growthFactor: settings.growthFactor,
minLoadFactor: settings.minLoadFactor,
bucketA: newBucket[K, V](settings.bucketSize, hashA, compare),
bucketB: newBucket[K, V](settings.bucketSize, hashB, compare),
return false
}
func (t *table[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
if t.capacity == 0 {
return insertion, true
}
slot := &t.slots[t.location(insertion.key)]
if !slot.occupied {
slot.entry = insertion
slot.occupied = true
t.size++
return
}
if t.compare(slot.key, insertion.key) {
slot.value = insertion.value
return
}
insertion, slot.entry = slot.entry, insertion
return insertion, true
}
func newTable[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) table[K, V] {
return table[K, V]{
hash: hash,
capacity: capacity,
compare: compare,
size: 0,
slots: make([]slot[K, V], capacity),
}
}
func pipe[X, Y, Z any](a func(X) Y, b func(Y) Z) func(X) Z {
return func(x X) Z { return b(a(x)) }
}
// NewTableBy creates a [Table] for any key type by using keyFunc to derive a
// comparable key. Two keys with the same derived key are treated as equal.
func NewTableBy[K, V any, C comparable](keyFunc func(K) C, options ...Option) *Table[K, V] {
return NewCustomTable[K, V](
pipe(keyFunc, NewDefaultHash[C]()),
pipe(keyFunc, NewDefaultHash[C]()),
func(a, b K) bool { return keyFunc(a) == keyFunc(b) },
options...,
)
}
// NewTable creates a [Table] using the default [Hash] and [EqualFunc]. Use
// the [Option] functions to configure its behavior. Note that this constructor
// is only provided for comparable keys. For arbitrary keys, consider
// [NewTableBy] or [NewCustomTable].
func NewTable[K comparable, V any](options ...Option) *Table[K, V] {
return NewCustomTable[K, V](NewDefaultHash[K](), NewDefaultHash[K](), DefaultEqualFunc[K], options...)
}