If i have such code which uses Composition using K...

# getting-started

[Vaibhav Jaiswal]

If i have such code which uses Composition using Kotlin delegate

interface Walk {
    fun walk()
}

class CatWalk : Walk {
    override fun walk(){
        println("Cat is walking")
    }
}

class Cat : Walk by CatWalk() {
    override fun walk(){
        println("Cat is running")
    }
}

fun main() {
    val cat = Cat()
    cat.walk()
}

This works fine as all functions are implemented by CatWalk
but I want Walk interface to have some function lets say eat() which i dont want CatWalk class to implement but let the class Cat provide its implementation, how can i do so?

I tried making CatWalk an abstract class and let Cat provide the implementation but it did not work that way
Is there any way to achieve such behaviour?

[CLOVIS]

interface Walk {
    fun walk()
    fun eat()
}

interface CatWalk : Walk {
    override fun walk() {
        println("Cat is walking")
    }
}

class Cat : Walk, CatWalk
// ^ doesn't compile, 'eat' isn't implemented

[CLOVIS]

If you're overriding (most) implementations provided by the delegate, you probably don't want to use delegates at all.

[Vaibhav Jaiswal]

I have a use case like this

interface Walk {
    fun walk()
    fun eat()
}

class CatWalk : Walk {
    override fun walk(){
        //how can i do this?
        showSnackBar("Cat is walking")
    }
    override fun eat() {
        showToast("Eat")
    }
}

class BaseCat {
    fun showSnackBar(message: String) {
       
    }
    
    fun showToast(message: String) {
        
    }
}

class Cat : BaseCat, Walk by CatWalk() {
}

How can i achieve this, I cannot pass the Cat instance in CatWalk constructor, it gives me error
I cant have abstract fun in CatWalk

[Vaibhav Jaiswal]

Basically, all my screens extend a BaseScreen which has such utility methods, now i want to add features to Screens using Composition, but i want to call functions which are in the base class BaseScreen
I hope you understand what i mean to say

[Vaibhav Jaiswal]

Currently i have to rely on default functions of interfaces, but that stops me from implementing variables, for which i have to create another class UseCase in this case
Example

interface PostActionHandler : KoinComponent {

    val postActionUseCase: PostActionUseCase
    val component: BaseComponent
    val onNavEvent: (AppNavEvents) -> Unit
    val navigateForRemote: Boolean
        get() = false

    fun handlePostAction(action: PostAction) = with(action) {
        trackPostAction(this)
        when (this) {
            is PostAction.AuthorClick -> handlePostAuthorClick(post)
            is PostAction.Clicked -> handlePostClick(post)
            is PostAction.GroupClick -> handleGroupClick(group)
            is PostAction.LikeToggle -> handlePostLike(post)
            is PostAction.ImageClick -> handlePostImageClick(post, index)

[CLOVIS]

Delegation isn't like inheritance. When using delegation, you are delegating to an existing object. You cannot override things from that object. The only thing you can do is 'shadow' them. I don't think you want to use delegation, here.

[Vaibhav Jaiswal]

Then whats the best approach I can go for to achieve this, my approach of leveraging default functions of interface helps, but only for functions and not variables

[CLOVIS]

If you need overrideable state, use an abstract class. But I don't really see why multiple screens would have the same state.

[Vaibhav Jaiswal]

My main use case is to add interactions
Like a feature of "Creating a Post", which if extended by any class, will have all code to do this, but as this is an interface i cannot keep any state or variable in it

[Vaibhav Jaiswal]

I have to create another class and then add wrapper variables to achieve it

Example:

interface CreatePostFeature {

    val createPostUseCase: CreatePostUseCase
    val component: BaseComponent
    val refType: PostReferenceType
    val onNavEvent: (AppNavEvents) -> Unit
    val localPostsEventBus: LocalPostEventBus

    val imagesLeft
        get() = CreatePostUseCase.maxImageCount - images.size

    val imagePickerFeature: ImagePickerFeature?
        get() = null

    val scope
        get() = component.componentScope

    val text: TextFieldValue
        get() = createPostUseCase.text

    val images
        get() = createPostUseCase.images

    val link
        get() = createPostUseCase.link

[CLOVIS]

How many different screens do you have that allow creating posts?

[Vaibhav Jaiswal]

Around 4 screens implement this interface
All they have to do is implement the variables which dont have a default getter

But i dont want this extra UseCase class for variables and add wrapper variables to access those,
Rather create the stateFlow, mutableState etc directly