In my kmp iOS app, I'm trying to create a `Set<Foo>`, where `Foo` is just a simple interface w...

# multiplatform

[Sterling Albury]

In my kmp iOS app, I'm trying to create a Set<Foo>, where Foo is just a simple interface with a couple of functions defined in commonMain, and if I try to declare or instantiate this set in swift, I get the error "Type 'Foo' does not conform to protocol 'Hashable'". Is there a way to make my interface Hashable or is there another good way to have sets of my interface?

[Paul Woitaschek]

You can wrap it in a swift struct and implement the protocol there and delegate for the values

[Sterling Albury]

ok cool, I'll give that a shot. thanks!

[Sterling Albury]

actually I'm confused...am I wrapping the set in the struct? I have a swift classes that implement the interface, but how do I define the set?

[Paul Woitaschek]

Can you post the code you are talking about?

[Sterling Albury]

so in my common main, I have

interface Foo {
    fun something()
}

and in my swift code I want to have a set of Foo, like so

var fooSet: Set<Foo>

but this line gives me that error about Foo not being Hashable.
I have implementations of Foo that I want to create the set from, in kotlin and swift, but how do I even declare the set?

[Paul Woitaschek]

From what I understand you can't. It doesn't confirm hashable

[Paul Woitaschek]

But you can go with SwiftFoo and implement the protocol there

[Sterling Albury]

that's really unfortunate. I don't need to implement the interface, I need the data structure to hold it. maybe I have to use a list or an array?

[Paul Woitaschek]

Yeah that will work

[Sterling Albury]

it's crazy to me that I can't have set's of my class in swift. Even if I define a class that has, say a function with a param of a Set<Foo> , I can't use it in swift? It's actually going to be pretty rough to try and change that data structure

[Sterling Albury]

maybe i can use expect/actual to create a delegate somehow

[Sterling Albury]

if I try to use KotlinMutableSet or KotlinArray, I get an error 'KotlinArray' is ambiguous for type lookup in this context ..any idea what that's about?

[Grégory Lureau]

Maybe you can define hashCode/equals method in your interface?
No default implementation, just the standard definition from Any functions. I presume that Any enforce those methods but you could pass an instance from Swift that doesn't matches those requirements.

[Grégory Lureau]

interface Foo {
    override operator fun equals(other: Any?): Boolean
    override fun hashCode(): Int
}

[russhwolf]

Try defining extension Foo: Hashable in Swift.

[Sterling Albury]

adding those functions didn't seem to work.
if I try to define extension Foo : Hashable I get an error "Extension of protocol 'Foo' cannot have an inheritance clause".