From 1cccb55bc11115139c15b0515160b00902e585e4 Mon Sep 17 00:00:00 2001
From: "Vladimir G." <vglazunov@renci.org>
Date: Fri, 7 Feb 2025 10:51:33 -0500
Subject: [PATCH] Added Singleton

---
 Misc/Initialization.go            | 28 ++++++++++++++++++++++++++++
 Tests/Misc/Initialization_test.go | 19 +++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 Misc/Initialization.go
 create mode 100644 Tests/Misc/Initialization_test.go

diff --git a/Misc/Initialization.go b/Misc/Initialization.go
new file mode 100644
index 0000000..53f2dba
--- /dev/null
+++ b/Misc/Initialization.go
@@ -0,0 +1,28 @@
+package Misc
+
+import "sync"
+
+type Singleton[T any] struct {
+	once sync.Once
+	Val  Nullable[T]
+	Init func() Result[T]
+}
+
+func NewSingleton[T any](f func() Result[T]) *Singleton[T] {
+	return &Singleton[T]{
+		Init: f,
+		Val:  NewNullable[T](),
+	}
+}
+
+func (this *Singleton[T]) Get() Result[T] {
+	var err error
+	this.once.Do(func() {
+		if this.Val.IsNil {
+			newObj := this.Init()
+			this.Val.Value = newObj.Value
+			err = newObj.Err
+		}
+	})
+	return Result[T]{Value: this.Val.Value, Err: err}
+}
diff --git a/Tests/Misc/Initialization_test.go b/Tests/Misc/Initialization_test.go
new file mode 100644
index 0000000..82099be
--- /dev/null
+++ b/Tests/Misc/Initialization_test.go
@@ -0,0 +1,19 @@
+package Misc
+
+import (
+	"github.com/RENCI/GoUtils/Misc"
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func Test_Singleton(t *testing.T) {
+
+	r := 1
+	s := Misc.NewSingleton(func() Misc.Result[int] {
+		r += 1
+		return Misc.NewResult(r, nil)
+	})
+	res := s.Get()
+	res = s.Get()
+	assert.Equal(t, 2, res.Value)
+}