Reference properties using `by`, `is`, or somethin...

# language-proposals

[Hullaballoonatic]

Reference properties using by, is, or something like that

current:

var foo = 3

var bar
    get() = foo
    set(v) {
        foo = v
    }

proposed:

var foo = 3
var bar by foo

[diesieben07]

This is ambiguous, since this currently means "use the value of foo as a delegated property", not "delegate to `foo`"

[diesieben07]

What would be nice though is var bar by ::foo

[igor.wojda]

BTW @Hullaballoonatic take a look at this https://stackoverflow.com/questions/45074596/delegate-property-to-another-property

[diesieben07]

Yes, but it would be nice for this to be optimized by the compiler.

[simon.vergauwen]

What would be optimized? Seems like you could make Alias from the github link inline even.

I wouldn't complicate the compiler nor the language for something that you can so elegantly solve in the language already.

[diesieben07]

seems you are right, this works nicely:

operator fun <T, R> KProperty1<T, R>.getValue(thisRef: T, prop: KProperty<*>): R = get(thisRef)
operator fun <T, R> KMutableProperty1<T, R>.setValue(thisRef: T, prop: KProperty<*>, newValue: R) = set(thisRef, newValue)

Should be able to be optimized by the JVM

[Hullaballoonatic]

@diesieben07 shame though that your solution, while elegant, cannot be used an interface (because no delegation in interfaces), while the getter setter version does

[karelpeeters]

https://youtrack.jetbrains.com/issue/KT-8658