Merge pull request #34 from MSE99/feature/map

Add `Map` to option package

Author: BooleanCat

option/option.go

@@ -85,3 +85,15 @@ func (o Option[T]) IsNone() bool {
 func (o Option[T]) Value() (T, bool) {
 	return o.value, o.present
 }
+
+// Map allows functions to work with option types, the returned
+// closure will only invoke fn if Option[T] is a Some variant.
+func Map[T any, U any](fn func(T) U) func(Option[T]) Option[U] {
+	return func(o Option[T]) Option[U] {
+		if o.IsNone() {
+			return None[U]()
+		}
+
+		return Some(fn(o.Unwrap()))
+	}
+}

option/option_test.go

@@ -72,6 +72,31 @@ func ExampleOption_Value() {
 	// true
 }
 
+func ExampleMap() {
+	posOnly := func(x int) option.Option[int] {
+		if x < 0 {
+			return option.None[int]()
+		}
+
+		return option.Some(x)
+	}
+
+	doubleNum := func(x int) int {
+		return x * 2
+	}
+
+	optDouble := option.Map(doubleNum)
+
+	n := posOnly(-5)
+	p := posOnly(25)
+
+	resultN := optDouble(n)
+	resultP := optDouble(p)
+
+	fmt.Println(resultN) // option.None
+	fmt.Println(resultP) // option.Some(50)
+}
+
 func TestSomeStringer(t *testing.T) {
 	assert.Equal(t, fmt.Sprintf("%s", option.Some("foo")), "Some(foo)")
 	assert.Equal(t, fmt.Sprintf("%s", option.Some(42)), "Some(42)")
@@ -139,3 +164,30 @@ func TestNoneValue(t *testing.T) {
 	assert.Equal(t, value, 0)
 	assert.False(t, ok)
 }
+
+func TestMapSome(t *testing.T) {
+	fn := func(x int) bool {
+		return x > 50
+	}
+
+	optFn := option.Map(fn)
+
+	resultWithSome := optFn(option.Some(40))
+
+	unwrappedSome, ok := resultWithSome.Value()
+	assert.True(t, ok)
+	assert.False(t, unwrappedSome)
+}
+
+func TestMapNone(t *testing.T) {
+	fn := func(x int) bool {
+		t.Error("fn was called!")
+		return x > 50
+	}
+
+	optFn := option.Map(fn)
+	resultWithNone := optFn(option.None[int]())
+
+	_, ok := resultWithNone.Value()
+	assert.False(t, ok)
+}