I’m trying out the new Context Parameters feature. They can be used on properties, but seems the con...

# language-proposals

[alexhelder]

I’m trying out the new Context Parameters feature. They can be used on properties, but seems the context applies to both the getter and setter. Would it make sense to be able to specify different context for getter and setter? For example, I have Preferences and MutablePreferences, and the context for get() should be Preferences, and the context for set(value) should be MutablePreferences

[Youssef Shoaib [MOD]]

You could duplicate it maybe:

context(l: List<T>)
@set:Deprecated("", level = DeprecationLevel.HIDDEN)
var <T> first get() = l.first()
set(value) { TODO() }
context(l: MutableList<T>)
@get:JvmName("getMutFirst")
@set:JvmName("setMutFirst")
@get:Deprecated("", level = DeprecationLevel.HIDDEN)
var <T> first get() = l.first()
set(value) { l[0] = value }

fun main() = with(listOf(1)) {
    println(first)
    with(mutableListOf(1)) {
    	println(first)
        first = 2
    	println(first)
	}
}

[alexhelder]

Never would have thought of that, thanks

[Youssef Shoaib [MOD]]

I can't guarantee that this will always continue working of course. In fact, the first one had to be a var because otherwise it caused issues.

[hfhbd]

Shouldn’t it be possible with an extension?

[alexhelder]

@hfhbd this could work, but notice code duplication in `get`:

val Preferences.serverAddress: ServerAddress?
    get() = get(Keys.SERVER_HOST)
        ?.let { ServerAddress(it) }

var MutablePreferences.serverAddress: ServerAddress?
    set(serverAddress) {
        if (serverAddress == null || serverAddress.value.isEmpty()) {
            remove(Keys.SERVER_HOST)
        } else {
            set(Keys.SERVER_HOST, serverAddress.value)
        }
    }
    get() = get(Keys.SERVER_HOST)
        ?.let { ServerAddress(it) }

Preferences and MutablePreferences are from jetpack DataStore, an external lib

[Youssef Shoaib [MOD]]

val Preferences.serverAddress: ServerAddress?
    get() = get(Keys.SERVER_HOST)
        ?.let { ServerAddress(it) }

var MutablePreferences.serverAddress: ServerAddress?
    set(serverAddress) {
        if (serverAddress == null || serverAddress.value.isEmpty()) {
            remove(Keys.SERVER_HOST)
        } else {
            set(Keys.SERVER_HOST, serverAddress.value)
        }
    }
    get() = (this as Preferences).serverAddress

[alexhelder]

That’s great, thanks everyone

[ephemient]

one slight tweak and you can avoid the explicit cast

val Preferences.serverAddress: ServerAddress?
    get() { ... }

var MutablePreferences.serverAddress: ServerAddress?
    get() = run(Preferences::serverAddress)
    set(value) { ... }