docs: congruency target

## Description

Closes #11.

## Changes

### Design Decisions

## Checklist

- [ ] Tests pass
- [ ] Docs updated

Reviewed-on: #21
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

.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

@@ -6,6 +6,19 @@ on:
   pull_request:
 
 jobs:
+  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
@@ -39,6 +52,14 @@ jobs:
       - 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

.gitignore

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

.golangci.yml

@@ -114,6 +114,9 @@ linters:
     # Reports uses of functions with replacement inside the testing package.
     - usetesting
 
+    # Reports mixed receiver types in structs/interfaces.
+    - recvcheck
+
   settings:
     revive:
       rules:
@@ -198,7 +201,7 @@ linters:
 
         # warns when initialism, variable or package naming conventions are not followed.
         - name: var-naming
-
+    
     misspell:
       # Correct spellings using locale preferences for US or UK.
       # Setting locale to US will correct the British spelling of 'colour' to 'color'.

.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

@@ -1,4 +1,4 @@
-.PHONY: all help install clean test-unit test-mutation test-fuzz test docs lint-go lint-makefile lint
+.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}'
@@ -16,10 +16,12 @@ test-unit: ## Run unit tests with coverage
 test-mutation: ## Run mutation tests with gremlins
 	gremlins unleash
 
+FUZZ_TIME ?= 30
+
 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=30s; \
+		go test ./... -fuzz="^$$func$$" -fuzztime=$(FUZZ_TIME)s; \
 	done
 
 test: test-unit test-mutation test-fuzz ## Run all tests
@@ -30,7 +32,10 @@ lint-go: ## Lint Go code
 lint-makefile: ## Lint the Makefile
 	checkmake Makefile
 
-lint: lint-go lint-makefile ## Lint all code
+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)"

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).

adr/001_interface_design.md

@@ -0,0 +1,542 @@
+# Designing an Idiomatic API Interface
+
+We (the maintainers) built `go-cuckoo`'s API interface without design intent.
+Up until now, we paid more attention implementing the underlying functionality of the cuckoo hashing.
+
+With the fundamentals of the algorithm built, we should revisit the interface.
+It should align closer to the following principles:
+
+- **Congruency**
+  A `go-cuckoo` table should have the same core functionality as Go's built-in map.
+
+- **Familiarity**
+  A `go-cuckoo` table should behave similarly to Go's standard map, so users will intuitively know how to use it.
+  In effect, its users will carry less cognitive load.
+
+## Current State
+
+### Interface of the built-in Map
+
+Listed below is every interface provided by Go to the built-in map object.
+Also included, are the functions from the package `maps` in the standard library.
+
+<details>
+<summary>Interfaces</summary>
+
+| #   | built-in Interface                 | Description                                                                                                                                           |
+| --- | ---------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------- |
+| 1   | `m := make(map[K]V)`               | Returns an empty map using the built-in `make()` function.                                                                                            |
+| 2   | `m := make(map[K]V, hint)`         | Returns an empty map using `make()`, with a capacity 'hint'. This hint is how many items the map expects to hold, _not_ a measure of how large it is. |
+| 3   | `m := map[K]V{...}`                | Returns a map, which may be filled with entries in the ellipsis (optional).                                                                           |
+| 4   | `var m map[K]V`                    | Defines an empty _variable_ that holds a map. This differs from #1 because `m` is uninitialized (nil) here.                                           |
+| 5   | `m[k] := v`                        | Assigns the value of `k` to `v`.                                                                                                                      |
+| 6   | `v := m[k]`                        | Returns the value of `k` if it exists. Otherwise, `v` is uninitialized.                                                                               |
+| 7   | `v, ok := m[k]`                    | Similar to #6, except `ok` is equal to whether `v` is initialized. This is comma-ok notation.                                                         |
+| 8   | `for k, v := range m`              | Iterates over every key-value pair in `m`. The order is random.                                                                                       |
+| 9   | `delete(m, k)`                     | Unassigns the value `k`. Returns no value.                                                                                                            |
+| 10  | `clear(m)`                         | Unassigns all keys in `m`. Returns no value.                                                                                                          |
+| 11  | `n := len(m)`                      | Returns the number of entries in `m`. If nil, `m` returns 0.                                                                                          |
+| 12  | `m2 := maps.Clone(m)`              | Returns a copy of `m`.                                                                                                                                |
+| 13  | `maps.Copy(dst, src)`              | Assigns every entry of `src` in `dst`.                                                                                                                |
+| 14  | `ok := maps.Equal(m1, m2)`         | Returns true iff `m1` and `m2` the same entries.                                                                                                      |
+| 15  | `ok := maps.EqualFunc(m1, m2, fn)` | Like #14, but with a custom comparator for non-comparable values.                                                                                     |
+| 16  | `maps.DeleteFunc(m, fn)`           | Removes every entry in `m` which satisfies `fn`. Returns no value.                                                                                    |
+| 17  | `it2 := maps.All(m)`               | Returns an 2D iterator over every key-value pair.                                                                                                     |
+| 18  | `it := maps.Keys(m)`               | Returns an iterator over every key.                                                                                                                   |
+| 19  | `it := maps.Values(m)`             | Returns an iterator over every value. There can be duplicates.                                                                                        |
+| 20  | `m := maps.Collect(seq)`           | Returns a map, with every entry defined in a 2D iterator over key-value pairs.                                                                        |
+| 21  | `maps.Insert(m, seq)`              | Assigns to `m` all key-value pairs in 2D iterator `seq`. Returns no value.                                                                            |
+
+</details>
+
+### Interface of `go-cuckoo`
+
+On the other hand, here is the current contract for `go-cuckoo`.
+
+<details>
+<summary>Interfaces</summary>
+
+| #   | built-in Interface                                 | Description                                                                                                                  |
+| --- | -------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------- |
+| 1   | `m := New(opts...)`                                | Creates a table using the default hash and equal function. The options configure its behavior. Confined to comparable keys.  |
+| 2   | `m := NewBy(keyFunc, opts...)`                     | Like #1, but allows any key type. A `keyFunc` is used to derive a comparable key.                                            |
+| 3   | `m := NewCustom(hashA, hashB, equalFunc, opts...)` | Like #1, but allows control over the hashes used to allow any key type. An `equalFunc` determines key equality.              |
+| 4   | `seq := m.Entries()`                               | Returns an unordered 2D iterator of all key-value pairs in the table.                                                        |
+| 5   | `v := m.Find(k)`                                   | Removes the value for `k`. Returns true if `k` existed.                                                                      |
+| 6   | `v, ok := m.Get(k)`                                | Returns the value for `k` in the table. Also, returns true if the `k` exists, otherwise false. When false, `v` is undefined. |
+| 7   | `ok := m.Has(k)`                                   | Returns true if `k` is in the table.                                                                                         |
+| 8   | `err := m.Put(k, v)`                               | Sets value `v` for key `k`. Otherwise, returns error.                                                                        |
+| 9   | `n := m.Size()`                                    | Returns the number of items in `m`.                                                                                          |
+| 10  | `str := m.String()`                                | Returns `m` as a string in the format "table[k1:v1 k2:v2 ...]".                                                              |
+| 11  | `cap := m.TotalCapacity()`                         | Returns how many slots `m` has allocated.                                                                                    |
+| 12  | `ok := m.Drop(k)`                                  | Removes `k` from the table. Returns whether the key had existed.                                                             |
+
+</details>
+
+### Determining Congruency
+
+So, how does the core functionality compare?
+Listed below is an analysis of every interface in Go's standard map.
+Each is compared against what `go-cuckoo` offers, and categorized into the following groups:
+
+- ✅ Covered: an analog exists.
+- ⚠️ Partial: workaround available.
+- ❌ Gap: no analog yet; addressed in [Target State](#solving-congruency).
+
+Specifically, here we are checking for functionality.
+Is there functionality that this offers which `go-cuckoo` does not?
+We are checking accessibility, but not discoverability.
+The latter will be considered later.
+
+<details>
+<summary>✅ <code>m := make(map[K]V)</code></summary>
+
+The analog is `m := New()`.
+
+</details>
+
+<details>
+<summary>⚠️ <code>m := make(map[K]V, hint)</code></summary>
+
+This has no simple analog.
+
+It is close to `m := New(Capacity(hint))`, but it assigns starting capacity, not expected size.
+For the built-in map, these are two separate things.
+
+- Capacity is an internal measure, used to optimize space/speed.
+  It is hidden from the user because it depends on the underlying implementation, which may change.
+- Expected size requires the map must hold a number of items before resizing.
+  This is tangeable and agnostic to implementation, hence why it is given to the user.
+
+In short, this interface defines expected size, but `Capacity()` defines capacity.
+
+</details>
+
+<details>
+<summary>❌ <code>m := map[K]V{...}</code></summary>
+
+This has no simple analog, the closest being:
+
+```go
+m := New[K, V]()
+for k, v := range startingEntries {
+  m.Put(k, v)
+}
+```
+
+It is idiomatic, but far less ergonomic.
+
+</details>
+
+<details>
+<summary>✅ <code>var m map[K]V</code></summary>
+
+The analog is `var m Table[K, V]`.
+
+</details>
+
+<details>
+<summary>✅ <code>m[k] := v</code></summary>
+
+The analog is `err := m.Put(k, v)`.
+
+</details>
+
+<details>
+<summary>✅ <code>v := m[k]</code></summary>
+
+The analog is `v := m.Find(k)`.
+
+</details>
+
+<details>
+<summary>✅ <code>v, ok := m[k]</code></summary>
+
+The analog is `v, ok := m.Get(k)`.
+
+</details>
+
+<details>
+<summary>✅ <code>for k, v := range m</code></summary>
+
+The analog is `for k, v := range m.Entries()`.
+
+</details>
+
+<details>
+<summary>✅ <code>delete(m, k)</code></summary>
+
+The analog is `ok := m.Drop(k)`.
+
+</details>
+
+<details>
+<summary>❌ <code>clear(m)</code></summary>
+
+There is no analog.
+
+The easiest may to do this is to delete all items individually:
+
+```go
+for k := range m.Entries() {
+  m.Drop(k)
+}
+```
+
+</details>
+
+<details>
+<summary>✅ <code>n := len(m)</code></summary>
+
+The analog is `n := m.Size()`.
+
+</details>
+
+<details>
+<summary>❌ <code>m2 := maps.Clone(m)</code></summary>
+
+There is no analog.
+
+The easiest way to do this currently is to make a new map, and manually add the items.
+
+```go
+m2 := cuckoo.Table[K, V]()
+
+for k, v := range m.Entries() {
+  m2.Put(k, v)
+}
+```
+
+This gets complicated by the various options available to the user.
+Furthermore, any custom `EqualFunc`, `keyFunc` or `Hash` is not transferred.
+
+</details>
+
+<details>
+<summary>❌ <code>maps.Copy(dst, src)</code></summary>
+
+There is no analog.
+
+The simplest way to do this is with a for-loop.
+
+```go
+for k, v := range src.Entries() {
+  dst.Put(k, v)
+}
+```
+
+</details>
+
+<details>
+<summary>❌ <code>ok := maps.Equal(m1, m2)</code></summary>
+
+There is no analog.
+
+Users have to manually check the key-value pairs to determine equality.
+
+</details>
+
+<details>
+<summary>❌ <code>ok := maps.EqualFunc(m1, m2, fn)</code></summary>
+
+There is no analog.
+
+Users have to manually check the key-value pairs to determine equality.
+
+</details>
+
+<details>
+<summary>❌ <code>maps.DeleteFunc(m, fn)</code></summary>
+
+There is no analog.
+
+Users have to manually delete keys.
+
+</details>
+
+<details>
+<summary>✅ <code>it2 := maps.All(m)</code></summary>
+
+The analog is `it2 := m.Entries()`.
+
+</details>
+
+<details>
+<summary>⚠️ <code>it := maps.Keys(m)</code></summary>
+
+There is no simple analog.
+
+A close neighbor is `it2 := m.Entries()`.
+Users can use this in a for-loop, and pick out just the keys:
+
+```go
+for k := range m.Entries() {
+  // ...
+}
+```
+
+</details>
+
+<details>
+<summary>⚠️ <code>it := maps.Values(m)</code></summary>
+
+There is no simple analog.
+
+A close neighbor is `it2 := m.Entries()`.
+Users can use this in a for-loop, and pick out just the values:
+
+```go
+for _, v := range m.Entries() {
+  // ...
+}
+```
+
+</details>
+
+<details>
+<summary>❌ <code>m := maps.Collect(seq)</code></summary>
+
+There is no analog.
+
+</details>
+
+<details>
+<summary>❌ <code>maps.Insert(m, seq)</code></summary>
+
+There is no analog.
+
+</details>
+
+## Target State
+
+### Solving Congruency
+
+We should make the following changes to accomodate for congruency:
+
+<details>
+<summary><code>ok := maps.EqualFunc(m1, m2, fn)</code></summary>
+
+We should implement a new function:
+
+```go
+func EqualFunc[K, V1, V2 any](t1 *Table[K, V1], t2 *Table[K, V2], eq func(V1, V2) bool) bool
+```
+
+This function is free, and not bound as a receiver function.
+(It is called `cuckoo.Equal(t1, t2)`, not `t1.Equals(t2)`.)
+The latter implies `t1` has authority, when in fact neither do.
+
+We define equality as:
+
+1. Neither table has a key the other doesn't.
+2. Each key has the same value in each table.
+   Parameter `eq` determines this equality.
+
+Custom `EqualFunc`'s complicate this, as they modulate key identity in tables.
+If two tables may differ on whether two keys are different, this function might break.
+So, we must assume that:
+
+- Both tables have `EqualFunc`'s which 'agree' on the identity of the keys present in the tables.
+  Agreement is defined as: if two keys are distinct in one table, they are distinct in the other.
+
+The name `EqualFunc` is already taken by `EqualFunc[K, V]`: an alias for `func(a, b K) bool`.
+Inlining `EqualFunc[K, V]` would solve this problem.
+We will move the documentation attached to it to `DefaultEqualFunc`.
+
+</details>
+
+<details>
+<summary><code>ok := maps.Equal(m1, m2)</code></summary>
+
+We should implement a new function, to conform with the standard library:
+
+```go
+func Equal[K any, V comparable](t1, t2 *Table[K, V]) bool
+```
+
+It uses the same equality check as in `EqualFunc`.
+Once again, the function is free because it is symmetric.
+
+</details>
+
+<details>
+<summary><code>maps.Insert(m, seq)</code></summary>
+
+We should implement a new receiver for the table:
+
+```go
+func (t *Table[K, V]) Insert(seq iter.Seq2[K, V]) error
+```
+
+A receiver fits better even though `maps.Insert` is a free function, because copying it is asymmetric.
+Map `dst` receives entries from map `src`.
+It's only free because Go's standard map is built into the language, and so cannot have receivers.
+
+In terms of naming, `t.Extend` is more accurate, and has precedent in [Python](docs.python.org/3/tutorial/datastructures.html#more-on-lists) and [Rust](https://doc.rust-lang.org/std/iter/trait.Extend.html).
+When [adding iterator function](https://github.com/golang/go/issues/61900) to the `maps` package, the Go team chose to frame it as 'sources' and 'sinks'.
+With this model, `maps.Insert` made more sense than `maps.Extend`.
+Ultimately, `t.Insert()` is a better choice to be consistent with `maps`.
+
+</details>
+
+<details>
+<summary><code>maps.Copy(dst, src)</code></summary>
+
+We should implement a new receiver for the table:
+
+```go
+func (t *Table[K, V]) Copy(src *Table[K, V]) error
+```
+
+It's functionality should match that of `t.Insert()`.
+
+A receiver fits better even though `maps.Copy` is a free function, 'copying' it is asymmetric: `dst` is writen into by `src`.
+It is only free because Go's standard map is built into the language, and so cannot have receivers.
+
+The name `t.Merge()` might be more accurate, but it does work because:
+
+- `t.Copy()` matches Go's built-in `copy()`, and `io.Copy()`. The Go team used [the same logic](https://github.com/golang/go/discussions/47330#discussioncomment-1167799) to name `maps.Copy()`.
+  In this case, `t.Merge()` would be an outlier.
+- `t.Merge()` implies some sort of conflict-resolution, when there is not.
+  It simply overwrites the values.
+
+</details>
+
+<details>
+<summary><code>maps.DeleteFunc(m, fn)</code></summary>
+
+We should implement a new receiver for the table:
+
+```go
+func (t *Table[K, V]) DeleteFunc(del func(K, V) bool)
+```
+
+It would have the same functionality as `maps.DeleteFunc`.
+
+A free function could work here, but `t` has clear authority over `del`.
+Other than being consistent with the `maps` package, `t.DeleteFunc` follows the Go convention of appending `Func` to higher-order equivalents of functions.
+This trumps names like `t.DeleteIf`, which lend more to [Java](https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#removeIf-java.util.function.Predicate-) or [C++](https://en.cppreference.com/cpp/algorithm/remove).
+The word `Delete` is also convention, tying back to the built-in `delete()`.
+
+</details>
+
+<details>
+<summary><code>m := maps.Collect(seq)</code></summary>
+
+We should implement a new constructor.
+
+```go
+func Collect[K comparable, V any](seq iter.Seq2[K, V]) (*Table[K, V], error)
+```
+
+It would create a `New()` table, and insert all entries in `seq`.
+
+This reveicer only supports the standard table constructor, with comparable keys.
+It is tempting to add `CollectBy` or `CollectCustom` to support all table types, but doing so would pollute the public interface.
+
+It would be just one more line to initialize the table and then call `t.Insert` directly:
+
+```go
+t := // ...
+err := t.Insert(seq)
+```
+
+</details>
+
+<details>
+<summary><code>m := map[K]V{...}</code></summary>
+
+We should make a new constructor, because entries are generic.
+So, creating an option with inialized entries doesn't work.
+
+With the previous additions, users have a few options.
+If they want to use a `New()` table, `t.Collect` matches well:
+
+```go
+t, err := cuckoo.Collect(func(yield func(K, V) bool) {
+    yield(key1, val1)
+    yield(key2, val2)
+})
+```
+
+For `NewCustom()` or `NewBy()` tables, users can call `t.Insert` after initialization:
+
+```go
+t := // ...
+err := t.Insert(func(yield func(K, V) bool) {
+    yield(key1, val1)
+    yield(key2, val2)
+})
+```
+
+It is one more line.
+But, the alternative is polluting the public interface with corresponding `*WithEntries` constuctors.
+
+</details>
+
+<details>
+<summary><code>m := make(map[K]V, hint)</code></summary>
+
+We should add a new option:
+
+```go
+func ExpectedSize(n int) Option
+```
+
+When fed to a table, it will allocate enough space to hold `n` entries without a resize.
+
+</details>
+
+<details>
+<summary><code>clear(m)</code></summary>
+
+We should implement a new receiver:
+
+```go
+func (t *Table[K, V]) Clear()
+```
+
+It will remove all entries from the table.
+
+</details>
+
+<details>
+<summary><code>m2 := maps.Clone(m)</code></summary>
+
+We should implement a matching function:
+
+```go
+func (t *Table[K, V]) Clone() *Table[K, V]
+```
+
+Also, it will copy the hash, equality function, and options used in the table.
+
+</details>
+
+<details>
+<summary><code>it := maps.Keys(m)</code></summary>
+
+We should implement a matching function:
+
+```go
+func (t *Table[K, V]) Keys() iter.Seq[K]
+```
+
+It is tempting to just have `All()`, but it returns a `Seq2`, not a `Seq`.
+There is no iterator adaptor between `Seq` and `Seq2`, and will not be for the foreseeable future.
+This function, while it feels superfluous, is required.
+
+</details>
+
+<details>
+<summary><code>it := maps.Values(m)</code></summary>
+
+We should implement a matching function:
+
+```go
+func (t *Table[K, V]) Values() iter.Seq[V]
+```
+
+For the same reason we need `Keys()`, we also need `Values()`.
+
+</details>

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

@@ -1,73 +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),
-	}
-}

compare.go

@@ -2,7 +2,7 @@ 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].
+// 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.

compare_example_test.go

@@ -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))
 

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.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 {
+				ok := actual.Drop(step.key)
+				_, has := expected[step.key]
+				assert.Equal(ok, has)
+
+				delete(expected, step.key)
+
+				_, ok = actual.Get(step.key)
+				assert.False(ok)
+			} else {
+				err := actual.Put(step.key, step.value)
+				assert.NoError(err)
+
+				expected[step.key] = step.value
+
+				found, ok := actual.Get(step.key)
+				assert.True(ok)
+				assert.Equal(step.value, found)
+			}
+
+			assert.Equal(expected, maps.Collect(actual.Entries()))
 		}
 	})
 }

cuckoo_internal_test.go

@@ -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())
 	}
 }

cuckoo_test.go

@@ -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)
@@ -107,24 +108,119 @@ func TestGetMany(t *testing.T) {
 	}
 
 	for i := range 2_000 {
-		value, err := table.Get(i)
+		value, ok := table.Get(i)
 		if i < 1_000 {
-			assert.NoError(err)
+			assert.True(ok)
 			assert.Equal(value, true)
 		} else {
-			assert.Error(err)
+			assert.False(ok)
 		}
 	}
 }
 
-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))
+	had := table.Drop(key)
 
-	err := table.Put(0, true)
-	assert.NoError(err)
-
-	assert.True(table.Has(0))
+	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.New[int, bool]()
+
+	had := table.Drop(key)
+
+	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.New[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.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)
+	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.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"}))
 }

doc.go

@@ -1,9 +1,12 @@
 // 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.
 //
+// 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

doc_example_test.go

@@ -8,25 +8,25 @@ 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)
 	}
 
-	if item, err := table.Get(1); err != nil {
-		fmt.Println("Error:", err)
+	if item, ok := table.Get(1); !ok {
+		fmt.Println("Not Found 1!")
 	} else {
 		fmt.Println("Found 1:", item)
 	}
 
-	if item, err := table.Get(0); err != nil {
-		fmt.Println("Error:", err)
+	if item, ok := table.Get(0); !ok {
+		fmt.Println("Not Found 0!")
 	} else {
 		fmt.Println("Found 0:", item)
 	}
 
 	// Output:
 	// Found 1: Hello, World!
-	// Error: key '0' not found
+	// Not Found 0!
 }

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=
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+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.
 //
@@ -7,14 +9,20 @@ package cuckoo
 const DefaultCapacity uint64 = 16
 
 // DefaultGrowthFactor is the standard resize multiplier for a [Table]. Most
-// hash table implementations use 2.
+// 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
@@ -23,23 +31,25 @@ type settings struct {
 }
 
 // An Option modifies the settings of a [Table]. It is used in its constructors
-// like [NewTable], for example.
+// 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 subtable of the [Table]. The
+// 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) }
 }

subtable.go

@@ -0,0 +1,107 @@
+package cuckoo
+
+// 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]
+	occupied bool
+}
+
+type subtable[K, V any] struct {
+	hash           Hash[K]
+	slots          []slot[K, V]
+	capacity, size uint64
+	compare        EqualFunc[K]
+}
+
+// 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
+}
+
+func (t *subtable[K, V]) get(key K) (value V, found bool) {
+	if t.capacity == 0 {
+		return
+	}
+
+	slot := t.slots[t.location(key)]
+	return slot.value, slot.occupied && t.compare(slot.key, key)
+}
+
+func (t *subtable[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
+}
+
+func (t *subtable[K, V]) resized(capacity uint64) *subtable[K, V] {
+	return &subtable[K, V]{
+		slots:    make([]slot[K, V], capacity),
+		capacity: capacity,
+		hash:     t.hash,
+		compare:  t.compare,
+	}
+}
+
+func (t *subtable[K, V]) update(key K, value V) (updated bool) {
+	if t.capacity == 0 {
+		return
+	}
+
+	slot := &t.slots[t.location(key)]
+
+	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) {
+	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 newSubtable[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) *subtable[K, V] {
+	return &subtable[K, V]{
+		hash:     hash,
+		capacity: capacity,
+		compare:  compare,
+		size:     0,
+		slots:    make([]slot[K, V], capacity),
+	}
+}

table.go

@@ -1,126 +1,206 @@
 package cuckoo
 
 import (
+	"errors"
 	"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].
+// ErrBadHash occurs when the hashes given to a [Table] cause too many key
+// 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. A different [Hash] algorithm.
+var ErrBadHash = errors.New("bad hash")
+
+// A Table which uses cuckoo hashing to resolve collision. Create
+// one with [New]. Or if you want more granularity, use [NewBy] or
+// [NewCustom].
 type Table[K, V any] struct {
-	bucketA, bucketB bucket[K, V]
-	growthFactor     uint64
-	minLoadFactor    float64
+	tableA, tableB *subtable[K, V]
+	growthFactor   uint64
+	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 {
-	return t.bucketA.capacity + t.bucketB.capacity
+func (t *Table[K, V]) TotalCapacity() uint64 {
+	return t.tableA.capacity + t.tableB.capacity
 }
 
 // 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)
+func (t *Table[K, V]) Size() int {
+	return int(t.tableA.size + t.tableB.size)
 }
 
 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())
+func (t *Table[K, V]) maxEvictions() int {
+	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})
+func (t *Table[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
 	}
 
-	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.tableA.update(entry.key, entry.value) {
+		return
+	}
+
+	if t.tableB.update(entry.key, entry.value) {
+		return
+	}
+
+	for range t.maxEvictions() {
+		if entry, homeless = t.tableA.insert(entry); !homeless {
+			return
+		}
+
+		if entry, homeless = t.tableB.insert(entry); !homeless {
+			return
 		}
 	}
 
-	return nil
+	return entry, true
 }
 
-// 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
+// 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,
+		tableA:        t.tableA.resized(capacity),
+		tableB:        t.tableB.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
+		}
 	}
 
-	if item, ok := t.bucketB.get(key); ok {
-		return item, nil
+	*t = *updated
+	return true
+}
+
+// grow increases the table's capacity by the growth factor. 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.tableA.capacity * t.growthFactor
 	}
 
-	return value, fmt.Errorf("key '%v' not found", key)
+	return t.resize(newCapacity)
+}
+
+// shrink reduces the table's capacity by the growth factor. It may
+// reduce it down to 0.
+func (t *Table[K, V]) shrink() bool {
+	return t.resize(t.tableA.capacity / t.growthFactor)
+}
+
+// Get fetches the value for a key in the [Table]. Matches the comma-ok pattern
+// of a builtin map; see [Table.Find] for plain indexing.
+func (t *Table[K, V]) Get(key K) (value V, ok bool) {
+	if item, ok := t.tableA.get(key); ok {
+		return item, true
+	}
+
+	if item, ok := t.tableB.get(key); ok {
+		return item, true
+	}
+
+	return
+}
+
+// Find fetches the value of a key. Matches direct indexing of a builtin map;
+// see [Table.Get] for a comma-ok pattern.
+func (t *Table[K, V]) Find(key K) (value V) {
+	value, _ = t.Get(key)
+	return
 }
 
 // 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
+func (t *Table[K, V]) Has(key K) (exists bool) {
+	_, exists = t.Get(key)
+	return
 }
 
-// Put sets the value for a key. Returns error if its value cannot be set.
+// 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) {
-	if t.bucketA.update(key, value) {
-		return nil
-	}
+	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 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 fmt.Errorf("could not redistribute entries into larger table: %w", 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
+// existed.
+func (t *Table[K, V]) Drop(key K) bool {
+	occupied := t.tableA.drop(key) || t.tableB.drop(key)
+
 	if t.load() < t.minLoadFactor {
-		return fmt.Errorf("bad hash: resize on load %d/%d = %f", t.Size(), t.Capacity(), t.load())
+		// The error is not handled here, because table-shrinking is an internal
+		// optimization.
+		t.shrink()
 	}
 
-	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")
+	return occupied
 }
 
 // Entries returns an unordered sequence of all key-value pairs in the table.
-func (t Table[K, V]) Entries() iter.Seq2[K, V] {
+func (t *Table[K, V]) Entries() iter.Seq2[K, V] {
 	return func(yield func(K, V) bool) {
-		for _, slot := range t.bucketA.slots {
+		for _, slot := range t.tableA.slots {
 			if slot.occupied {
 				if !yield(slot.key, slot.value) {
 					return
@@ -128,7 +208,7 @@ func (t Table[K, V]) Entries() iter.Seq2[K, V] {
 			}
 		}
 
-		for _, slot := range t.bucketB.slots {
+		for _, slot := range t.tableB.slots {
 			if slot.occupied {
 				if !yield(slot.key, slot.value) {
 					return
@@ -139,8 +219,8 @@ func (t Table[K, V]) Entries() iter.Seq2[K, V] {
 }
 
 // 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 {
+// "table[k1:v1 k2:v2 ...]".
+func (t *Table[K, V]) String() string {
 	var sb strings.Builder
 	sb.WriteString("table[")
 
@@ -158,13 +238,13 @@ func (t Table[K, V]) String() string {
 	return sb.String()
 }
 
-// NewCustomTable creates a [Table] with custom [Hash] and [EqualFunc]
+// NewCustom 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] {
+func NewCustom[K, V any](hashA, hashB Hash[K], compare EqualFunc[K], options ...Option) *Table[K, V] {
 	settings := &settings{
 		growthFactor:  DefaultGrowthFactor,
 		bucketSize:    DefaultCapacity,
-		minLoadFactor: DefaultMinimumLoad,
+		minLoadFactor: defaultMinimumLoad,
 	}
 
 	for _, option := range options {
@@ -174,8 +254,8 @@ func NewCustomTable[K, V any](hashA, hashB Hash[K], compare EqualFunc[K], option
 	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),
+		tableA:        newSubtable[K, V](settings.bucketSize, hashA, compare),
+		tableB:        newSubtable[K, V](settings.bucketSize, hashB, compare),
 	}
 }
 
@@ -183,10 +263,10 @@ 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
+// NewBy 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](
+func NewBy[K, V any, C comparable](keyFunc func(K) C, options ...Option) *Table[K, V] {
+	return NewCustom[K, V](
 		pipe(keyFunc, NewDefaultHash[C]()),
 		pipe(keyFunc, NewDefaultHash[C]()),
 		func(a, b K) bool { return keyFunc(a) == keyFunc(b) },
@@ -194,10 +274,10 @@ func NewTableBy[K, V any, C comparable](keyFunc func(K) C, options ...Option) *T
 	)
 }
 
-// NewTable creates a [Table] using the default [Hash] and [EqualFunc]. Use
+// New 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...)
+// [NewBy] or [NewCustom].
+func New[K comparable, V any](options ...Option) *Table[K, V] {
+	return NewCustom[K, V](NewDefaultHash[K](), NewDefaultHash[K](), DefaultEqualFunc[K], options...)
 }