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x/mobile/cmd/gomobile: type conversion not working on iOS #17369

jotdl opened this issue Oct 6, 2016 · 0 comments

x/mobile/cmd/gomobile: type conversion not working on iOS #17369

jotdl opened this issue Oct 6, 2016 · 0 comments


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@jotdl jotdl commented Oct 6, 2016


I have a (hopefully small) issue with type conversion related to usage of gomobile:

What version of Go are you using (go version)?

go version go1.7.1 darwin/amd64
gomobile version +6ea0bb5 Wed Oct 5 13:16:13 2016 +0000 (android,ios); androidSDK=/Users/.../Library/Android/sdk/platforms/android-23

What operating system and processor architecture are you using (go env)?


What did you do?

  1. Write code with composed interface. Can be something like
type Car interface {
    WheelCount() int
type Limousine interface {
    Seats() int
    SetSeats(seats int)

Full go code is available at Go Code
2. Generate go mobile bindings for iOS and android, e.g.
gomobile bind -target=ios data
3. Create platform specific app and call a go method which tries to do type conversion. Type conversion may be:

func PrintCar(car Car) {
    fmt.Println("Car: ", car)
    fmt.Println("Wheels: ", car.WheelCount())

    limousine, ok := car.(Limousine)
    fmt.Println("Limousine cast was ", ok, ", Content:", limousine)
    if ok {
        fmt.Println("Seats: ", limousine.Seats())

and platform specific code like this for iOS

id<GoDataLimousine> car = GoDataNewLimousine();
[car setSeats:5];
  1. Execute the program on iOS or Android

What did you expect to see?

Type conversion from Car to Limousine should be possible if the object fulfills Limousine.
Output of type conversion on Go, iOS and Android:

Car:  &{4 5}
Wheels:  4
Limousine cast was  true , Content: &{4 5}
Seats:  5

What did you see instead?

Type conversion is not possible on iOS between interfaces. Output of type conversion Go, Android (as expected):

Car:  &{4 5}
Wheels:  4
Limousine cast was  true , Content: &{4 5}
Seats:  5

iOS, fails to do type conversion. The limousine is stripped down to fulfill the car interface only and does not fulfill the limousine interface anymore:

Car:  &{42}
Wheels:  4
Limousine cast was  false , Content: <nil>

So in my understanding type conversion should work on iOS as it does on android and in normal go itself. But using gomobile on iOS, interfaces seem to loose other fulfilled interfaces once they're passed to a method which receives a specific interface only.

Or am I doing something wrong? Otherwise I would like to help solving this issue. Sadly I am new to the go mobile tooling itself. Maybe somebody can point me into the right direction?

Is this intentionally not working or is it expected to work?

Thanks for your help!

@quentinmit quentinmit added this to the Unreleased milestone Oct 6, 2016
@jotdl jotdl changed the title x/mobile/cmd/gomobile: type conversion differs on android and iOS x/mobile/cmd/gomobile: type conversion not working on iOS Oct 8, 2016
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