x/mobile/bind: support slices of supported structs

[scisci]

Just want to know if it will ever be possible to support slices of supported. I currently have to write a wrapper object around an array to pass it back and forth between IOS and Go.

[bradfitz]

/cc @crawshaw @hyangah

[hyangah]

It will not be impossible and eventually it should be supported. I don't know anyone who's currently working on this problem.

[dcu]

yeah this is the most frustrating issue for me right now

[weitzj]

Do you have any ideas when this will be done? What I could do?

I tried and failed using: https://golang.org/pkg/container/list/ as an alternative

[ioArchman]

+1
Would highly recommend this as currently falling short without this.

[mpiannucci]

This is stopping me from using gomobile in anything worthwhile at the moment

[ioArchman]

@scisci - If you don't mind can you please share across a gist on how you handle the problem currently as said? My requirement would be to return an array/slice of custom modal class objects with 4 string properties.

[scisci]

hi @ioArchman, I made a quick repo here:

https://github.com/scisci/go-mobile-collection

If you think it can work for you, you will probably want to fork it and modify the render.go function to add/remove the methods you want on your collection wrapper. Feel free to make a comment on the project if you have any questions. Its pretty directly adapted from another tutorial on go generics, which you can find here http://www.onebigfluke.com/2014/12/generic-programming-go-generate.html

Keep in mind, I don't consider this a good solution. It feels hacky working with a wrapper on the objective-c/swift side, but it does work. Really would prefer something that feels more natural.

[ioArchman]

Thanks @scisci. Will look into this and try utilizing for now. Agreed on your last point too.

[scisci]

hi @hyangah, do you have any hints on how this would be technically implemented in case someone wanted to attempt it from outside the gomobile team?

[anacrolix]

👍

[anacrolix]

This is very limiting.

[kmcrawford]

Is this still on the road map? I found this library and would like to use it, but this issue may be keep me from using gomobile.

[kliron]

It seems this is a show-stopper for many people. Are there any plans to support this?

[4h0q]

What's the status of this issue? It has been around for quite a while. It looks like the main show stopper for many people.

CC: @hyangah @crawshaw

[dradtke]

I just ran into this, and it would be great to be able to support slices.

[saurabha5]

Just linking the stack overflow question here : https://stackoverflow.com/questions/44382115/golang-gomobile-tool-for-cross-platform-slices-of-struct-return-type

[nhatlee]

have any update for this issue?

[gituser9]

Will there be any news?

[hyangah]

Currently no one is working on the x/mobile project and adding this feature is not a small project.

Not ideal but need to work around by writing a wrapper package for binding, or using what @scisci mentioned for now.

[gituser9]

Does the project have a future?

[bradfitz]

It's community supported at this point, so its future depends on you. There are others from the community working on it, but not full time.

[MariusVanDerWijden]

Anyone currently working on this? If not, could you give some pointers where to start with this?

[makivlach]

As a really slow and dumb bypass, you could serialize the data into JSON, pass the string and unserialize it on the other side. Use this only as a last resort, though.

[korovan-software]

A workaround from my real project. Maybe will helpful for someone.
On Go side:

type Field struct {
    Key       string
    Value     string
    Protected bool
}

type FieldReceiver interface {
    Add(field *Field)
}

func GetEntryFields(receiver FieldReceiver) {
    for _, v := range entry.Values {
        field := Field{
            Key:       v.Key,
            Value:     v.Value.Content,
            Protected: v.Value.Protected}
        receiver.Add(&field)
    }
}

Android side:

val fields = mutableListOf<Field>()
Mylib.getEntryFields() { field ->
    run {
        fields += Field(field.key, field.value, field.protected)
    }
}

[nrobi144]

A workaround with String as an example:

type StringCollection interface {
	Add(s string) StringCollection
	Get(i int) string
	Size() int
}

// TODO solve this with generics
type StringArray struct {
	items []string
}

func (array StringArray) Add(s string) StringArray {
	array.items = append(array.items, s)
	return array
}

func (array StringArray) Get(i int) string {
	return array.items[i]
}

func (array StringArray) Size() int {
	return len(array.items)
}

Usage in go:

func GetExampleStringArray() *StringArray {
	strings := []string{"example1", "example2"}
	return &StringArray{items: strings}
}

On Android you can use this extension to convert it to a List<String>:

fun StringArray.toStringList(): List<String> {
    val list = mutableListOf<String>()
    for (i in 0 until size()) {
        list.add(get(i))
    }
    return list
}

fun main() {
    GoPackage.getExampleStringArray().toStringList()
}

[tex0l]

Is there any news? I was very surprised that this isn't implemented by default, I need to make very ugly workarounds to make my binding work.

[coder-free]

Is there any news?

[kevmo314]

I've implemented most of the work required for slices of structs here: golang/mobile#101

I could certainly use some help on the final stretch though, especially if you've managed to get the gobind test environment working correctly. In particular, I think the last bits necessary are to:

1. Update the go-side refnum marshalling
2. Add an Obj-C implementation
3. Test that it all works

[gopherbot]

Change https://go.dev/cl/583196 mentions this issue: bind: support slices of structs