From 6c7506e5c476f49ef2700e45128d81baedeccfc7 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sat, 17 Aug 2024 23:12:23 -0400
Subject: Val

---
 val.go | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 val.go

diff --git a/val.go b/val.go
new file mode 100644
index 0000000..4d35fb9
--- /dev/null
+++ b/val.go
@@ -0,0 +1,53 @@
+package share
+
+// Val is a concurrent interface to a piece of shared data.
+//
+// A client can read the data by sending a channel via request, and the stored value will
+// be sent back via the channel. The client is responsible for closing the channel.
+//
+// The stored value can be changed by sending the new value via Set. Requests block until
+// the first value is received on Set.
+//
+// Val should be closed after use.
+type Val[T any] struct {
+	Request chan<- chan T
+	Set     chan<- T
+}
+
+func NewVal[T any]() Val[T] {
+	request := make(chan chan T)
+	set := make(chan T)
+	go func() {
+		val := <-set // wait for initial value
+		for {
+			select {
+			case v, ok := <-set:
+				if !ok { // closed
+					return
+				}
+				val = v
+			case req, ok := <-request:
+				if !ok { // closed
+					return
+				}
+				go func() { // don't wait for client to receive
+					req <- val
+				}()
+			}
+		}
+	}()
+	return Val[T]{request, set}
+}
+
+// Get makes a synchronous request and returns the stored value.
+func (v Val[T]) Get() T {
+	c := make(chan T)
+	defer close(c)
+	v.Request <- c
+	return <-c
+}
+
+func (v Val[T]) Close() {
+	close(v.Request)
+	close(v.Set)
+}
-- 
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