sync: Add Locker type

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

@@ -4,9 +4,15 @@ 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] (ctx context.Context, channels ...chan T) (int, T, bool) {
+func Select[T any, C ChannelRecv[T]] (ctx context.Context, channels ...C) (int, T, bool) {
 	var zero T
 
 	// add all channels as select cases
@@ -39,11 +45,12 @@ func Select[T any] (ctx context.Context, channels ...chan T) (int, T, bool) {
 		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] (ctx context.Context, channels ...chan T) <- chan T {
+func Combine[T any, C ChannelRecv[T]] (ctx context.Context, channels ...C) <- chan T {
 	channel := make(chan T)
 	// our silly slection routine
 	go func () {