Support #OrElse() that supports to return the Option value accord…

…ing to the actual value existence

Close #20

Signed-off-by: moznion <moznion@mail.moznion.net>

README.md

@@ -60,6 +60,7 @@ and more detailed examples are here: [./examples_test.go](./examples_test.go).
 - [Option[T]#Take() (T, error)](https://pkg.go.dev/github.com/moznion/go-optional#Option.Take)
 - [Option[T]#TakeOr(fallbackValue T) T](https://pkg.go.dev/github.com/moznion/go-optional#Option.TakeOr)
 - [Option[T]#TakeOrElse(fallbackFunc func() T) T](https://pkg.go.dev/github.com/moznion/go-optional#Option.TakeOrElse)
+- [Option[T]#OrElse(fallbackOptionValue Option[T]) Option[T]](https://pkg.go.dev/github.com/moznion/go-optional#Option.OrElse)
 - [Option[T]#Filter(predicate func(v T) bool) Option[T]](https://pkg.go.dev/github.com/moznion/go-optional#Option.Filter)
 - [Option[T]#IfSome(f func(v T))](https://pkg.go.dev/github.com/moznion/go-optional#Option.IfSome)
 - [Option[T]#IfSomeWithError(f func(v T) error) error](https://pkg.go.dev/github.com/moznion/go-optional#Option.IfSomeWithError)

examples_test.go

@@ -550,3 +550,17 @@ func ExampleFlatMapOrWithError() {
 	// err is nil: false
 	//
 }
+
+func ExampleOption_OrElse() {
+	fallback := Some[string]("fallback")
+
+	some := Some[string]("actual")
+	fmt.Printf("%s\n", some.OrElse(fallback))
+
+	none := None[string]()
+	fmt.Printf("%s\n", none.OrElse(fallback))
+
+	// Output:
+	// Some[actual]
+	// Some[fallback]
+}

option.go

@@ -102,6 +102,15 @@ func (o Option[T]) TakeOrElse(fallbackFunc func() T) T {
 	return o[value]
 }
 
+// OrElse returns the Option value according to the actual value existence.
+// If the receiver's Option value is Some, this function pass-through that to return. Otherwise, this value returns the `fallbackOptionValue`.
+func (o Option[T]) OrElse(fallbackOptionValue Option[T]) Option[T] {
+	if o.IsNone() {
+		return fallbackOptionValue
+	}
+	return o
+}
+
 // Filter returns self if the Option has a value and the value matches the condition of the predicate function.
 // In other cases (i.e. it doesn't match with the predicate or the Option is None), this returns None value.
 func (o Option[T]) Filter(predicate func(v T) bool) Option[T] {

option_test.go

@@ -568,3 +568,10 @@ func TestOption_String(t *testing.T) {
 	assert.Equal(t, "Some[mystr]", Some[*MyStringer](&MyStringer{}).String())
 	assert.Equal(t, "None[]", None[*MyStringer]().String())
 }
+
+func TestOption_OrElse(t *testing.T) {
+	fallback := Some[string]("fallback")
+
+	assert.EqualValues(t, Some[string]("actual").OrElse(fallback).Unwrap(), "actual")
+	assert.EqualValues(t, None[string]().OrElse(fallback).Unwrap(), "fallback")
+}