Test for functional argument passing (#336)

* Test for functional argument passing

testdata/calls.go

@@ -4,6 +4,22 @@ type Thing struct {
 	name string
 }
 
+type ThingOption func(*Thing)
+
+func WithName(name string) ThingOption {
+	return func(t *Thing) {
+		t.name = name
+	}
+}
+
+func NewThing(opts ...ThingOption) *Thing {
+	t := &Thing{}
+	for _, opt := range opts {
+		opt(t)
+	}
+	return t
+}
+
 func (t Thing) String() string {
 	return t.name
 }
@@ -36,6 +52,12 @@ func main() {
 	runFunc(func(i int) {
 		println("inside fp closure:", thing.String(), i)
 	}, 3)
+
+	// functional arguments
+	thingFunctionalArgs1 := NewThing()
+	thingFunctionalArgs1.Print("functional args 1")
+	thingFunctionalArgs2 := NewThing(WithName("named thing"))
+	thingFunctionalArgs2.Print("functional args 2")
 }
 
 func runFunc(f func(int), arg int) {

testdata/calls.txt

@@ -7,3 +7,5 @@ Thing.Print: foo arg: bar
 bound method: foo
 thing inside closure: foo
 inside fp closure: foo 3
+Thing.Print:  arg: functional args 1
+Thing.Print: named thing arg: functional args 2