2 Commits

Author SHA1 Message Date
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
11 changed files with 334 additions and 395 deletions

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@@ -114,9 +114,6 @@ linters:
# Reports uses of functions with replacement inside the testing package. # Reports uses of functions with replacement inside the testing package.
- usetesting - usetesting
# Reports mixed receiver types in structs/interfaces.
- recvcheck
settings: settings:
revive: revive:
rules: rules:

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

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@@ -68,22 +68,21 @@ func FuzzInsertLookup(f *testing.F) {
for _, step := range scenario.steps { for _, step := range scenario.steps {
if step.drop { if step.drop {
ok := actual.Drop(step.key) err := actual.Drop(step.key)
_, has := expected[step.key] assert.NoError(err)
assert.Equal(ok, has)
delete(expected, step.key) delete(expected, step.key)
_, ok = actual.Get(step.key) _, err = actual.Get(step.key)
assert.False(ok) assert.Error(err)
} else { } else {
err := actual.Put(step.key, step.value) err := actual.Put(step.key, step.value)
assert.NoError(err) assert.NoError(err)
expected[step.key] = step.value expected[step.key] = step.value
found, ok := actual.Get(step.key) found, err := actual.Get(step.key)
assert.True(ok) assert.NoError(err)
assert.Equal(step.value, found) assert.Equal(step.value, found)
} }

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@@ -108,12 +108,12 @@ func TestGetMany(t *testing.T) {
} }
for i := range 2_000 { for i := range 2_000 {
value, ok := table.Get(i) value, err := table.Get(i)
if i < 1_000 { if i < 1_000 {
assert.True(ok) assert.NoError(err)
assert.Equal(value, true) assert.Equal(value, true)
} else { } else {
assert.False(ok) assert.Error(err)
} }
} }
} }
@@ -124,9 +124,9 @@ func TestDropExistingItem(t *testing.T) {
table := cuckoo.New[int, bool]() table := cuckoo.New[int, bool]()
(table.Put(key, value)) (table.Put(key, value))
had := table.Drop(key) err := table.Drop(key)
assert.True(had) assert.NoError(err)
assert.Equal(0, table.Size()) assert.Equal(0, table.Size())
assert.False(table.Has(key)) assert.False(table.Has(key))
} }
@@ -136,9 +136,9 @@ func TestDropNoItem(t *testing.T) {
key := 0 key := 0
table := cuckoo.New[int, bool]() table := cuckoo.New[int, bool]()
had := table.Drop(key) err := table.Drop(key)
assert.False(had) assert.NoError(err)
assert.Equal(0, table.Size()) assert.Equal(0, table.Size())
assert.False(table.Has(key)) assert.False(table.Has(key))
} }
@@ -152,9 +152,10 @@ func TestDropItemCapacity(t *testing.T) {
) )
startingCapacity := table.TotalCapacity() startingCapacity := table.TotalCapacity()
table.Drop(key) err := table.Drop(key)
endingCapacity := table.TotalCapacity() endingCapacity := table.TotalCapacity()
assert.NoError(err)
assert.Equal(0, table.Size()) assert.Equal(0, table.Size())
assert.Equal(uint64(128), startingCapacity) assert.Equal(uint64(128), startingCapacity)
assert.Equal(uint64(64), endingCapacity) assert.Equal(uint64(64), endingCapacity)
@@ -202,9 +203,9 @@ func TestDropResizeCapacity(t *testing.T) {
err1 := table.Put(0, true) err1 := table.Put(0, true)
err2 := table.Put(1, true) err2 := table.Put(1, true)
table.Drop(1) err3 := table.Drop(1)
assert.NoError(errors.Join(err1, err2)) assert.NoError(errors.Join(err1, err2, err3))
assert.Equal(uint64(20), table.TotalCapacity()) assert.Equal(uint64(20), table.TotalCapacity())
} }

3
doc.go
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@@ -5,8 +5,5 @@
// a table with any key type using [NewCustom]. Custom [Hash] functions and // a table with any key type using [NewCustom]. Custom [Hash] functions and
// key comparison are also supported. // 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 // See more: https://en.wikipedia.org/wiki/Cuckoo_hashing
package cuckoo package cuckoo

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@@ -14,19 +14,19 @@ func Example_basic() {
fmt.Println("Put error:", err) fmt.Println("Put error:", err)
} }
if item, ok := table.Get(1); !ok { if item, err := table.Get(1); err != nil {
fmt.Println("Not Found 1!") fmt.Println("Error:", err)
} else { } else {
fmt.Println("Found 1:", item) fmt.Println("Found 1:", item)
} }
if item, ok := table.Get(0); !ok { if item, err := table.Get(0); err != nil {
fmt.Println("Not Found 0!") fmt.Println("Error:", err)
} else { } else {
fmt.Println("Found 0:", item) fmt.Println("Found 0:", item)
} }
// Output: // Output:
// Found 1: Hello, World! // Found 1: Hello, World!
// Not Found 0! // Error: key '0' not found
} }

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@@ -7,9 +7,9 @@ import (
// A Hash function maps any data to a fixed-length value (in this case, a // A Hash function maps any data to a fixed-length value (in this case, a
// [uint64]). // [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 // 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]. // [maphash.Comparable].
// //
// [chaotic]: https://en.wikipedia.org/wiki/Avalanche_effect // [chaotic]: https://en.wikipedia.org/wiki/Avalanche_effect

237
hash_table.go Normal file
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@@ -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 buckets, 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 [HashTable.growthFactor]. 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 [HashTable.growthFactor]. 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 h2: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...)
}

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@@ -2,39 +2,34 @@ package cuckoo
import "fmt" import "fmt"
// DefaultCapacity is the initial capacity of a [Table]. It is inspired from // DefaultCapacity is the initial capacity of a [HashTable]. It is inspired from
// Java's [HashMap] implementation, which also uses 16. // Java's [HashMap] implementation, which also uses 16.
// //
// [HashMap]: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#HashMap-- // [HashMap]: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#HashMap--
const DefaultCapacity uint64 = 16 const DefaultCapacity uint64 = 16
// DefaultGrowthFactor is the standard resize multiplier for a [Table]. Most // DefaultGrowthFactor is the standard resize multiplier for a [HashTable]. Most
// implementations use 2. // implementations use 2.
const DefaultGrowthFactor uint64 = 2 const DefaultGrowthFactor uint64 = 2
// defaultMinimumLoad is the default lowest acceptable occupancy of a [Table]. // defaultMinimumLoad is the default lowest acceptable occupancy of a [HashTable].
// The higher the minimum load, the more likely that a [Table.Put] will not // The higher the minimum load, the more likely that a [HashTable.Put] will not
// succeed. The value of 5% is taken from [libcuckoo]. // succeed. The value of 5% is taken from [libcuckoo].
// //
// [libcuckoo]: https://github.com/efficient/libcuckoo/blob/656714705a055df2b7a605eb3c71586d9da1e119/libcuckoo/cuckoohash_config.hh#L21 // [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 { type settings struct {
growthFactor uint64 growthFactor uint64
minLoadFactor float64 minLoadFactor float64
bucketSize uint64 bucketSize uint64
} }
// An Option modifies the settings of a [Table]. It is used in its constructors // An Option modifies the settings of a [HashTable]. It is used in its constructors
// like [New], for example. // like [New], for example.
type Option func(*settings) type Option func(*settings)
// Capacity modifies the starting capacity of each subtable of the [Table]. The // Capacity modifies the starting capacity of each bucket of the [HashTable]. The
// value must be non-negative. // value must be non-negative.
func Capacity(value int) Option { func Capacity(value int) Option {
if value < 0 { if value < 0 {
@@ -44,7 +39,7 @@ func Capacity(value int) Option {
return func(s *settings) { s.bucketSize = uint64(value) } return func(s *settings) { s.bucketSize = uint64(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. // it must resize. The value must be greater than 1.
func GrowthFactor(value int) Option { func GrowthFactor(value int) Option {
if value < 2 { if value < 2 {

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@@ -1,107 +0,0 @@
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),
}
}

306
table.go
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@@ -1,283 +1,103 @@
package cuckoo package cuckoo
import ( type entry[K, V any] struct {
"errors" key K
"fmt" value V
"iter"
"math/bits"
"strings"
)
// 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 {
tableA, tableB *subtable[K, V]
growthFactor uint64
minLoadFactor float64
} }
// TotalCapacity returns the number of slots allocated for the [Table]. To get the type slot[K, V any] struct {
// number of slots filled, look at [Table.Size]. entry[K, V]
func (t *Table[K, V]) TotalCapacity() uint64 { occupied bool
return t.tableA.capacity + t.tableB.capacity
} }
// Size returns how many slots are filled in the [Table]. type table[K, V any] struct {
func (t *Table[K, V]) Size() int { hash Hash[K]
return int(t.tableA.size + t.tableB.size) slots []slot[K, V]
capacity, size uint64
compare EqualFunc[K]
} }
func log2(n uint64) (m int) { // location determines where in the bucket a certain key would be placed. If the
return max(0, bits.Len64(n)-1) // 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 { func (t table[K, V]) get(key K) (value V, found bool) {
return 3 * log2(t.TotalCapacity()) if t.capacity == 0 {
}
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
}
return float64(t.Size()) / float64(t.TotalCapacity())
}
// 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 return
} }
if t.tableB.update(entry.key, entry.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 return
} }
for range t.maxEvictions() { slot := &t.slots[t.location(key)]
if entry, homeless = t.tableA.insert(entry); !homeless {
return
}
if entry, homeless = t.tableB.insert(entry); !homeless { if slot.occupied && t.compare(slot.key, key) {
return slot.occupied = false
} t.size--
return true
} }
return entry, true return false
} }
// resized creates an empty copy of the table, with a new capacity for each func (t *table[K, V]) resize(capacity uint64) {
// bucket. t.slots = make([]slot[K, V], capacity)
func (t *Table[K, V]) resized(capacity uint64) *Table[K, V] { t.capacity = capacity
return &Table[K, V]{ t.size = 0
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 func (t table[K, V]) update(key K, value V) (updated bool) {
// the array, and replaces the current table. It is a helper function for if t.capacity == 0 {
// [Table.grow] and [Table.shrink]; use them instead. return
func (t *Table[K, V]) resize(capacity uint64) bool {
updated := t.resized(capacity)
for k, v := range t.Entries() {
if _, failed := updated.insert(entry[K, V]{k, v}); failed {
return false
}
} }
*t = *updated slot := &t.slots[t.location(key)]
return true
}
// grow increases the table's capacity by the growth factor. If the if slot.occupied && t.compare(slot.key, key) {
// capacity is 0, it increases it to 1. slot.value = value
func (t *Table[K, V]) grow() bool { return true
var newCapacity uint64
if t.TotalCapacity() == 0 {
newCapacity = 1
} else {
newCapacity = t.tableA.capacity * t.growthFactor
} }
return t.resize(newCapacity) return false
} }
// shrink reduces the table's capacity by the growth factor. It may func (t *table[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
// reduce it down to 0. if t.capacity == 0 {
func (t *Table[K, V]) shrink() bool { return insertion, true
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 { slot := &t.slots[t.location(insertion.key)]
return item, true
if !slot.occupied {
slot.entry = insertion
slot.occupied = true
t.size++
return
} }
return if t.compare(slot.key, insertion.key) {
} slot.value = insertion.value
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) {
_, exists = t.Get(key)
return
}
// Put sets the value for a key. If it cannot be set, an error is returned.
func (t *Table[K, V]) Put(key K, value V) (err error) {
var (
entry = entry[K, V]{key, value}
homeless bool
)
for range defaultGrowthLimit {
if entry, homeless = t.insert(entry); !homeless {
return
}
// 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) insertion, slot.entry = slot.entry, insertion
return insertion, true
} }
// Drop removes a value for a key in the table. Returns whether the key had func newTable[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) table[K, V] {
// existed. return table[K, V]{
func (t *Table[K, V]) Drop(key K) bool { hash: hash,
occupied := t.tableA.drop(key) || t.tableB.drop(key) capacity: capacity,
compare: compare,
if t.load() < t.minLoadFactor { size: 0,
// The error is not handled here, because table-shrinking is an internal slots: make([]slot[K, V], capacity),
// optimization.
t.shrink()
}
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] {
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 *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()
}
// NewCustom creates a [Table] 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) *Table[K, V] {
settings := &settings{
growthFactor: DefaultGrowthFactor,
bucketSize: DefaultCapacity,
minLoadFactor: defaultMinimumLoad,
}
for _, option := range options {
option(settings)
}
return &Table[K, V]{
growthFactor: settings.growthFactor,
minLoadFactor: settings.minLoadFactor,
tableA: newSubtable[K, V](settings.bucketSize, hashA, compare),
tableB: newSubtable[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 [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 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) },
options...,
)
}
// 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
// [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...)
}