Add optional (#170)

* Add optional

Wrapper container with easy to understand helper methods

* Add test and rewrite test

* Add panic test

* Add TestOrElseGetHappyPath

datastructure/optional/optional.go

@@ -0,0 +1,108 @@
+package optional
+
+import (
+	"sync"
+)
+
+// Optional is a type that may or may not contain a non-nil value.
+type Optional[T any] struct {
+	value *T
+	mu    sync.RWMutex
+}
+
+// Empty returns an empty Optional instance.
+func Empty[T any]() Optional[T] {
+	return Optional[T]{}
+}
+
+// Of returns an Optional with a non-nil value.
+func Of[T any](value T) Optional[T] {
+	return Optional[T]{value: &value}
+}
+
+// OfNullable returns an Optional for a given value, which may be nil.
+func OfNullable[T any](value *T) Optional[T] {
+	if value == nil {
+		return Empty[T]()
+	}
+	return Optional[T]{value: value}
+}
+
+// IsPresent checks if there is a value present.
+func (o Optional[T]) IsPresent() bool {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+
+	return o.value != nil
+}
+
+// IsEmpty checks if the Optional is empty.
+func (o Optional[T]) IsEmpty() bool {
+	return !o.IsPresent()
+}
+
+// IfPresent performs the given action with the value if a value is present.
+func (o Optional[T]) IfPresent(action func(value T)) {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+
+	if o.value != nil {
+		action(*o.value)
+	}
+}
+
+// IfPresentOrElse performs the action with the value if present, otherwise performs the empty-based action.
+func (o Optional[T]) IfPresentOrElse(action func(value T), emptyAction func()) {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+
+	if o.value != nil {
+		action(*o.value)
+	} else {
+		emptyAction()
+	}
+}
+
+// Get returns the value if present, otherwise panics.
+func (o Optional[T]) Get() T {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+
+	if o.value == nil {
+		panic("Optional.Get: no value present")
+	}
+	return *o.value
+}
+
+// OrElse returns the value if present, otherwise returns other.
+func (o Optional[T]) OrElse(other T) T {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+
+	if o.value != nil {
+		return *o.value
+	}
+	return other
+}
+
+// OrElseGet returns the value if present, otherwise invokes supplier and returns the result.
+func (o Optional[T]) OrElseGet(supplier func() T) T {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+
+	if o.value != nil {
+		return *o.value
+	}
+	return supplier()
+}
+
+// OrElseThrow returns the value if present, otherwise returns an error.
+func (o Optional[T]) OrElseThrow(errorSupplier func() error) (T, error) {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+
+	if o.value == nil {
+		return *new(T), errorSupplier()
+	}
+	return *o.value, nil
+}