Address nullability issue with Arb.edgecase

[Kantis]

An Arb<T>, where T is nullable currently has no way of expressing the null edgecase, since returning null from Arb.edgecase is interpreted as "no edgecase exists" by the property testing framework.

Suggestion

Change Arb<T>.edgecase(rs: RandomSource): T? to Arb<T>.edgecase(rs: RandomSource): Sample<T>?. Returning null can still be interpreted as no edgecase exists. Sample lets us box the null edgecase so it can be represented as well.

Reference

• Ticket for nullability in Arb.lists
• Attempted fix for above, which caused performance degradation for nested lists
• Ticket failed related to performance impact

[AlexCue987]

Is this a good use case for Kotlin's own Result?

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-result/

[Kantis]

Arb interface already uses Sample to communicate samples being pulled from the Arb.

kotest/kotest-property/src/commonMain/kotlin/io/kotest/property/Gen.kt

Line 108 in 7d07732

abstract fun sample(rs: RandomSource): Sample<A>