Hi there! I got this code: ``` @OptIn(Experimen...

# announcements

[Jose A.]

Hi there! I got this code:

@OptIn(ExperimentalContracts::class)
    private fun OriginQueryNode.isSimpleQuery(): Boolean {
        contract {
            returns(true) implies (this@isSimpleQuery is OriginQueryNode.FilterAttributes)
        }
        return this is OriginQueryNode.FilterAttributes && ...
    }

    private fun calculateMembersLocallyIfPossible(originQuery: OriginQueryNode): MemberGaussCollection? =
        if (originQuery.isSimpleQuery()) {
            println(originQuery.fieldOnlyFilterAttributes)
        }

In the `calculateMembersLocallyIfPossible`fun I try to access the field `fieldOnlyFilterAttributes`after checking isSimpleQuery is true. The contract should let me access the field but it's not working (marks fieldOnlyFilterAttributes as not existent.

[Jose A.]

If I change the check to this:

if (originQuery.isSimpleQuery() && originQuery is OriginQueryNode.FilterAttributes) {

then it works.

[Jose A.]

Why is the contract not working?

[nanodeath]

kinda seems like the contract isn't doing anything at all from here

[Jose A.]

Yep, but I don't know why... I tried a similar example:

import kotlin.contracts.ExperimentalContracts
import kotlin.contracts.contract


sealed class A(val a: String) {
	class B(val b: String): A("a")
}

@OptIn(ExperimentalContracts::class)
fun A.isNice(): Boolean {
    contract {
        returns(true) implies (this@isNice is A.B)
    }
    return this is A.B && b == "nice"
}

fun A.printIfNice() {
    if (isNice())
    	println("It's nice! ${this.b}")
}

fun main() {
    val someB = A.B("nice")
    
    someB.printIfNice()
}

And this works as expected

[nanodeath]

those do indeed look equivalent to me. is OriginQueryNode also a sealed class?

[Jose A.]

Yep, the simple example mimics the real code

[Jose A.]

sealed class OriginQueryNode {

    class FilterAttributes(
        val attributeName: String,
        val operator: ComparisonOperator,
        val comparables: List<String>,
        val comparablesAsExpression: List<String>
    ) : OriginQueryNode()

    class SetOperation(...) : OriginQueryNode()
}

[Jose A.]

Ok... This fun was inside a class, if I put it outside the class it works

@OptIn(ExperimentalContracts::class)
    private fun OriginQueryNode.isSimpleQuery(): Boolean {
        contract {
            returns(true) implies (this@isSimpleQuery is OriginQueryNode.FilterAttributes)
        }
        return this is OriginQueryNode.FilterAttributes && ...
    }

[Jose A.]

So as extension function inside class the contract does not work or it's not properly specified (probably the last)

[nanodeath]

huh. that's...unexpected. does that sound like a bug to you?

[Jose A.]

Probably not, I'll play a little more with the simple example to be sure

[nanodeath]

I'd double-check that the correct this is being checked in the contract block

[nanodeath]

the contract says this@isSimpleQuery but then the code right after just says this

[Jose A.]

Full simple example that replicates the problem in my original code:

import kotlin.contracts.ExperimentalContracts
import kotlin.contracts.contract


sealed class A(val a: String) {
    class B(val b: String) : A("a")
}

class OtherClass {
    fun someTest(a: A) {
        a.printIfNice()
    }

    @OptIn(ExperimentalContracts::class)
    private fun A.isNice(): Boolean {
        contract {
            returns(true) implies (this@isNice is A.B)
        }
        return this is A.B && b == "nice"
    }

    private fun A.printIfNice() {
        if (isNice()) {
            println(this.b)
        }
    }
}

fun main() {
    val someB = A.B("nice")
    val c = OtherClass()
    c.someTest(someB)
}

[Jose A.]

Converting isNice() receiver to parameter makes the example work

[nanodeath]

weird