feature: added optional

pkg/container/optional/optional.go

@@ -0,0 +1,6 @@
+package optional
+
+type Optional[T any] struct {
+	Present bool
+	Value   T
+}

pkg/container/optional/optional_factories.go

@@ -0,0 +1,23 @@
+package optional
+
+func Empty[T any]() *Optional[T] {
+	return &Optional[T]{
+		Present: false,
+	}
+}
+
+func OfAny[T any](value T) *Optional[T] {
+	return &Optional[T]{
+		Present: true,
+		Value:   value,
+	}
+}
+
+func OfNonDefault[T comparable](value T) *Optional[T] {
+	var defaultValue T
+	if value != defaultValue {
+		return Empty[T]()
+	} else {
+		return OfAny[T](value)
+	}
+}

pkg/container/optional/optional_methods.go

@@ -0,0 +1,59 @@
+package optional
+
+import "log"
+
+func (self *Optional[T]) IfPresent(action func(T)) {
+	if self.Present {
+		action(self.Value)
+	}
+}
+
+func (self *Optional[T]) OrElsePanic(err error) T {
+	return self.OrElsePanicF(func() error {
+		return err
+	})
+}
+
+func (self *Optional[T]) OrElsePanicF(errorSupplier func() error) T {
+	if self.Present {
+		return self.Value
+	}
+
+	err := errorSupplier()
+	panic(err)
+}
+
+func (self *Optional[T]) OrElseFatal(err error) T {
+	return self.OrElseFatalF(func() error {
+		return err
+	})
+}
+
+func (self *Optional[T]) OrElseFatalF(errorSupplier func() error) T {
+	if self.Present {
+		return self.Value
+	}
+
+	err := errorSupplier()
+	var returnStub T
+	log.Fatal(err)
+
+	// Компилятор без return не пропустит, но сюда никогда не дойдет из-за фатала выше.
+	return returnStub
+}
+
+func (self *Optional[T]) OrElse(defaultValue T) T {
+	if self.Present {
+		return self.Value
+	}
+
+	return defaultValue
+}
+
+func (self *Optional[T]) OrElseGet(defaultValueSupplier func() T) T {
+	if self.Present {
+		return self.Value
+	}
+
+	return defaultValueSupplier()
+}