Why private members are not passed from Cadence activities?

I noticed that when I use a struct consisting of both public and private members, then the private ones are not copied(?) by Cadence activities.

For example I have a struct:

package foo

type Foo struct {
    Name        string
    PublicList  []string
    privateList []string
}

func NewFoo() *Foo {
    return &Foo{
        Name:        "Test",
        PublicList:  []string{"A", "B", "C"},
        privateList: []string{"one", "two"},
    }
}

func (f *Foo) ShowLists() {
    fmt.Println("PublicList: ", f.PublicList, ", privateList: ", f.privateList)
}

I also use other struct, registered as activities struct:

package activities 

type FooActivities struct{}

func (a *FooActivities) NewFoo(ctx context.Context) (*foo.Foo, error) {
    return foo.NewFoo(), nil
}

func (a *FooActivities) ShowLists(ctx context.Context, f *foo.Foo) error {
    f.ShowLists()
    return nil
}

My workflow calls these two activities in a following way:

var f *foo.Foo
workflow.ExecuteActivity(ctx, fooActivities.NewFoo).Get(ctx, &f)
workflow.ExecuteActivity(ctx, fooActivities.ShowLists, f).Get(ctx, nil)

The result, printed by ShowLists function:

PublicList: [A B C] , privateList: []

Why is the private list not initialized as expected? Is this a bug or feature? I couldn't find answer for this question in the Cadence documentation.

Cadence (and Temporal) by default use json.Marshal to serialize and json.Unmarshall to deserialize activity arguments. It doesn't serialize private fields.

Here is a possible workaround.