Morning, is there a way to detail the inherited pr...

# announcements

[dasz]

Morning, is there a way to detail the inherited property type and still override it from the base class?
Example:

interface A; class AI: A; interface B (val a: A); class BI (override val a: AI): B

conversion from A -> to AI where AI derives from A

[Pavlo Liapota]

https://pl.kotl.in/QHS1kHqjn

[dasz]

Seems like it is up to Kotlin version

[dasz]

error: type of 'x' doesn't match the type of the overridden var-property 'public abstract var x: Line_0.FooBase defined in Line_0.BarBase'
        override var x: FooChild

Kotlin version 1.3.21 (JRE 1.8.0_152-release-1343-b01)

[dasz]

I've changed the 'x' to var

[diesieben07]

If it's a var it would violate the Liskov Substitution Principle:
The interface specifies that any interface instance can be assigned, but the implementation restricts that to only specific classes.

[diesieben07]

thats why it's not allowed

[diesieben07]

Example:

interface A {
    var foo: Any
}
class B : A(var foo: String)

val a: A = B("foo")
a.foo = 123 // compiles, because A.foo is any, but it's actually a B, which requires a String...

[dasz]

You are right, however where is the difference between var and val in that case? In both cases it breaks the Liskov Substitution Principle, however with 'val' it compiles as @Pavlo Liapota pointed

[diesieben07]

val only allows getting values out of the class. If the interface specifies "you can get an Any here" then "you can get a `String`" here satisfies that

[diesieben07]

With var however it breaks:
"You can put Any in here" is not satisfied by "You can put String in here"

[dasz]

Ok, thank you, I got your point