sync: Add Locker type

container/optional.go

@@ -1,31 +1,31 @@
 package ucontainer
 
-// Optional is an optional value.
+// Optional can either hold a value, or nothing.
 type Optional[T any] struct {
 	value T
 	exists bool
 }
 
-// Value returns the value and true if the value exists. If not, it returns the
+// O creates a new optional with the specified value.
-// last set value and false.
+func O[T any] (value T) Optional[T] {
-func (this *Optional[T]) Value () (T, bool) {
+	return Optional[T] {
-	return this.value, this.exists
+		value: value,
+		exists: true,
+	}
 }
 
-// Set sets the value.
+// Void returns an optional with no value.
-func (this *Optional[T]) Set (value T) {
+func Void[T any] () Optional[T] {
-	this.value = value
+	return Optional[T] { }
-	this.exists = true
-}
-
-// Unset unsets the value.
-func (this *Optional[T]) Unset () {
-	var zero T
-	this.value = zero
-	this.exists = false
 }
 
 // Exists returns if the value is currently set.
-func (this *Optional[T]) Exists () bool {
+func (optional Optional[T]) Exists () bool {
-	return this.exists
+	return optional.exists
+}
+
+// Value returns the value and true if the value exists. If not, it returns the
+// zero value and false.
+func (optional Optional[T]) Value () (T, bool) {
+	return optional.value, optional.exists
 }

container/set.go

@@ -3,6 +3,15 @@ package ucontainer
 // Set is a set of unique items, built on top of map.
 type Set[T comparable] map[T] struct { }
 
+// NewSet creates a new set that contains all specified items.
+func NewSet[T comparable] (items ...T) Set[T] {
+	set := make(Set[T])
+	for _, item := range items {
+		set.Add(item)
+	}
+	return set
+}
+
 // Empty returns true if there are no items in the set.
 func (set Set[T]) Empty () bool {
 	return set == nil || len(set) == 0

go.mod

@@ -1,3 +1,3 @@
 module git.tebibyte.media/sashakoshka/goutil
 
-go 1.20.0
+go 1.22.0

image/color/color_test.go

@@ -1,6 +1,23 @@
 package ucolor
 
 import "testing"
+import "image/color"
+
+func TestTransparent (test *testing.T) {
+	if Transparent(color.NRGBA { A: 255 }) {
+		test.Fatal("false positive")
+	}
+	if !Transparent(color.NRGBA { A: 0 }) {
+		test.Fatal("false negative")
+	}
+}
+
+func TestToRGBA (test *testing.T) {
+	rgba := ToRGBA(color.NRGBA { R: 123, G: 100, B: 23, A: 230 })
+	if rgba != (color.RGBA { R: 111, G: 90, B: 20, A: 230 }) {
+		test.Fatalf("wrong value: %v", rgba)
+	}
+}
 
 func TestPremultiply (test *testing.T) {
 	r, g, b, a := Premultiply(0xFFFF, 0xFFFF, 0xFFFF, 0x8888)

sync/gate.go

@@ -0,0 +1,94 @@
+package usync
+
+import "sync"
+
+// Error defines errors that this package can produce
+type Error string; const (
+	ErrAlreadyClosed Error = "AlreadyClosed"
+)
+
+// Error fullfills the error interface.
+func (err Error) Error () string {
+	return string(err)
+}
+
+// Gate wraps a channel and allows the receiver to abruptly stop receiving
+// messages without causing the sender to lock up.
+type Gate[T any] struct {
+	channel    chan T
+	lock       sync.RWMutex
+	open       bool
+	bufferSize int
+}
+
+// NewGate creates a new gate with no buffer.
+func NewGate[T any] () Gate[T] {
+	return Gate[T] {
+		channel: make(chan T),
+		open:    true,
+	}
+}
+
+// NewBufferedGate creates a new gate with a buffer.
+func NewBufferedGate[T any] (buffer int) Gate[T] {
+	return Gate[T] {
+		channel:    make(chan T, buffer),
+		open:       true,
+		bufferSize: buffer,
+	}
+}
+
+// Send sends and item to the channel, returning whether the item was sent.
+func (this *Gate[T]) Send (item T) bool {
+	this.lock.RLock()
+	defer this.lock.RUnlock()
+	if !this.open { return false }
+	this.channel <- item
+	return true
+}
+
+// Receive returns a receive-only channel that can be used to receive items.
+func (this *Gate[T]) Receive () <- chan T {
+	this.lock.RLock()
+	defer this.lock.RUnlock()
+	return this.channel
+}
+
+// Close closes the gate, drains all remaining messages, and closes the channel.
+func (this *Gate[T]) Close () error {
+	this.lock.Lock()
+	if !this.open { return ErrAlreadyClosed }
+	this.open = false
+	this.lock.Unlock()
+	for len(this.channel) > 0 { <- this.channel }
+	close(this.channel)
+	return nil
+}
+
+// Reset re-opens the gate if it is closed, and creates a new channel.
+func (this *Gate[T]) Reset () error {
+	this.lock.Lock()
+	defer this.lock.Unlock()
+	this.open = true
+	if this.channel != nil { close(this.channel) }
+	this.channel = make(chan T, this.bufferSize)
+	return nil
+}
+
+// Open returns whether the gate is open.
+func (this *Gate[T]) Open () bool {
+	this.lock.RLock()
+	defer this.lock.RUnlock()
+	return this.open
+}
+
+// Len returns the amount of items in the channel.
+func (this *Gate[T]) Len () int {
+	return len(this.channel)
+}
+
+// Cap returns the amount of items the channel can hold.
+func (this *Gate[T]) Cap () int {
+	return cap(this.channel)
+}
+

sync/locker.go

@@ -0,0 +1,36 @@
+package usync
+
+import "sync"
+
+// Locker guards access to a value
+type Locker[T any] struct {
+	value T
+	mutex sync.Mutex
+}
+
+// NewLocker creates a new locker with the specified value.
+func NewLocker[T any] (value T) Locker[T] {
+	return Locker[T] {
+		value: value,
+	}
+}
+
+// Set sets the value of the locker.
+func (this *Locker[T]) Set (value T) {
+	this.mutex.Lock()
+	defer this.mutex.Unlock()
+	this.value = value
+}
+
+// Borrow borrows the value from the locker, and returns a function that must
+// immediately be deferred, like this:
+//
+//   value, done := locker.Borrow()
+//   defer done()
+//
+// From the time Borrow is called to the time the done function is called, it is
+// safe to access the locked object from within the current goroutine.
+func (this *Locker[T]) Borrow () (T, func ()) {
+	this.mutex.Lock()
+	return this.value, this.mutex.Unlock
+}

sync/select.go

@@ -0,0 +1,85 @@
+package usync
+
+import "slices"
+import "context"
+import "reflect"
+
+// ChannelRecv is a type constraint that includes all channel types that can be
+// recieved from.
+type ChannelRecv[T any] interface {
+	~chan T | ~<- chan T
+}
+
+// A type-safe wrapper around reflect.Select. Taken from:
+// https://stackoverflow.com/questions/19992334
+func Select[T any, C ChannelRecv[T]] (ctx context.Context, channels ...C) (int, T, bool) {
+	var zero T
+
+	// add all channels as select cases
+	cases := make([]reflect.SelectCase, len(channels) + 1)
+	for i, ch := range channels {
+		cases[i] = reflect.SelectCase {
+			Dir:  reflect.SelectRecv,
+			Chan: reflect.ValueOf(ch),
+		}
+	}
+
+	// add ctx.Done() as another select case to stop listening when the
+	// context is closed
+	cases[len(channels)] = reflect.SelectCase {
+		Dir:  reflect.SelectRecv,
+		Chan: reflect.ValueOf(ctx.Done()),
+	}
+	
+	// read from the channel
+	chosen, value, ok := reflect.Select(cases)
+	if !ok {
+		if ctx.Err() != nil {
+			return -1, zero, false
+		}
+		return chosen, zero, false
+	}
+
+	// cast return value
+	if ret, ok := value.Interface().(T); ok {
+		return chosen, ret, true
+	}
+	return chosen, zero, false
+	
+}
+
+// Combine returns a channel that continuously returns the result of the select
+// until all input sources are exhauste, or the context is canceled.
+func Combine[T any, C ChannelRecv[T]] (ctx context.Context, channels ...C) <- chan T {
+	channel := make(chan T)
+	// our silly slection routine
+	go func () {
+		for {
+			if len(channels) < 2 {
+				// only the context is left, stop everything
+				close(channel)
+				return
+			}
+			// read new value
+			chosen, value, ok := Select(ctx, channels...)
+			if ok {
+				// we have a value
+				channel <- value
+			} else {
+				// a channel has been closed and we need to do
+				// something about it
+				if chosen == len(channels) - 1 {
+					// the context has expired, stop
+					// everything
+					close(channel)
+					return
+				} else {
+					// a normal channel has closed, remove
+					// it from the list
+					channels = slices.Delete(channels, chosen, chosen + 1)
+				}
+			}
+		}
+	} ()
+	return channel
+}

sync/select_test.go

@@ -0,0 +1,24 @@
+package usync
+
+import "time"
+import "testing"
+import "context"
+
+func TestSelect (test *testing.T) {
+	// https://stackoverflow.com/questions/19992334
+	c1 := make(chan int)
+	c2 := make(chan int)
+	c3 := make(chan int)
+	chs := []chan int { c1, c2, c3 }
+	go func () {
+		time.Sleep(time.Second)
+		c2 <- 42
+	} ()
+	ctx, done := context.WithTimeout(context.Background(), 5 * time.Second)
+	defer done()
+
+	chosen, val, ok := Select(ctx, chs...)
+	if !ok          { test.Fatal("not ok")                  }
+	if 1  != chosen { test.Fatal("expected 1, got", chosen) }
+	if 42 != val    { test.Fatal("expected 42, got", val)   }
+}