Compose execution observers in order

internal/observation/compose.go

@@ -0,0 +1,19 @@
+package observation
+
+// Compose copies and synchronously invokes non-nil observers in order.
+func Compose[T any, F ~func(T)](observers ...F) F {
+	selected := make([]F, 0, len(observers))
+	for _, observer := range observers {
+		if observer != nil {
+			selected = append(selected, observer)
+		}
+	}
+	if len(selected) == 0 {
+		return nil
+	}
+	return func(event T) {
+		for _, observer := range selected {
+			observer(event)
+		}
+	}
+}