alexarchambault/scalacheck-shapeless

Generation of arbitrary case classes / ADTs with scalacheck and shapeless

Luciano

@lJoublanc

I'll try it out.

Luciano

@lJoublanc

yeah that doesn't work :( trying to do Arbitrary[Int :+: Long]. On the other hand Arbitrary[AnyVal] does work, but I get lots of stuff I don't want (Unit) for example.

Georgi Krastev

@joroKr21

There is definitely an Arbitrary for Coproducts somewhere in there, maybe it's just not exposed. Look around the source code.

found it - MkCoproductArbitrary

Luciano

@lJoublanc

Thanks @joroKr21 will check it out today.

Marko Dimjašević

@mdimjasevic

Hi everyone!

I'd like to generate sequences of valid state machine transitions. Any idea how to do this with scalacheck-shapeless? I was thinking of using IndexedStateT from https://github.com/typelevel/cats/blob/master/core/src/main/scala/cats/data/IndexedStateT.scala to encode an input and output state of a transition.

Ihor Kaharlichenko

@kaharlichenko

Hi. Is there any way I could customize the generator for a case class? Suppose I have case class Person(name: String, age: Int) and I want age to be generated as Gen.posNum, while the rest of the field generators being derived?

Olli Helenius

@liff

@kaharlichenko well if you have arbPerson: Arbitrary[Person] you could do something like:

implicit val properArbPerson: Arbitrary[Person] = Arbitrary(arbPerson.arbitrary.flatMap(person => Gen.posInt.map(age => person.copy(age = age))))

alternatively you could create a distinct type for age, possibly with refined, newtype or otherwise. then you could just create an arbAge: Arbitrary[Age] and not worry about how a Person is generated

Ihor Kaharlichenko

@kaharlichenko

Well, changing the type of age is not an option, since that would involve changing the production code for the sake of testing. The second option is viable, though. Thank you.

Jason Pickens

@steinybot

Do the generated Arbitrarys ignore other implicits in scope? I haven’t been able to confirm or deny yet but it seems to be the case. For example:

case class Foo(bar: Bar)
implicit val arbBar: Arbitrary[Bar] = somePredefinedArbitraryForBar // This is not used
implicit val arbFoo: Arbitrary[Foo] = MkArbitrary[Foo].arbitrary

Jason Pickens

@steinybot

may have been a PBKAC error

Jason Pickens

@steinybot

Does the library work with recursive types?

I’m getting a StackOverflowError but it might just be me again

Paul Snively

@PaulAtFormation

Could someone please offer an example of generating a Shapeless Coproduct, presumably using the aforementioned MkCoproductArbitrary? I'm getting:

could not find implicit value for parameter mkArb: org.scalacheck.derive.MkCoproductArbitrary[takt.data.valkyrie.deployables.etl.VAL1081.ValkyrieType]

Alex

@unthingable

Hello. How does one confine generated String vals for a given case class to non-Unicode characters?

Daniel Sebban

@dsebban

Hi I am getting at runtime

ava.lang.IllegalArgumentException: requirement failed: Duration is limited to +-(2^63-1)ns (ca. 292 years)
[info]  at scala.concurrent.duration.FiniteDuration.<init>(Duration.scala:583)
[info]  at scala.concurrent.duration.Duration$.apply(Duration.scala:31)
[info]  at scala.concurrent.duration.package$DurationLong$.durationIn$extension(package.scala:48)
[info]  at scala.concurrent.duration.package$DurationLong.durationIn(package.scala:48)

is there a way to override the Duration generator implicit with a correct one

Gabriel Assis Bezerra

@gabriel-bezerra

as far as I know, the Arbitrary[T]s in scope are preferred instead of the derived ones

import /*the automatic derivation from the library*/

implicit val arbitraryDuration: Arbitrary[Duration] = ...

implicitly[Arbitrary[SomethingThatNeedsDuration]] // this should use arbitraryDuration

Luciano

@lJoublanc

Was just about to post practically the same question as above ... I have:

case class Dense[K: Field](layout: Layout, stride: Int)

but if I put an implicit val stride: Arbitrary[Int] = ... before forAll, in order to limit the values of stride, it's not being picked up. It sounds like the same problem as above?

Luciano

@lJoublanc

@dsebban how did you finally resolve your issue?

Luciano

@lJoublanc

Ah figured it out - it's the old 'shrink' problem ...

Edmondo Porcu

@edmondo1984

Hello everyone, how can I get my arbitrary for "integers"

to override a default one only for a specific field of a case class?

Luciano

@lJoublanc

Don't think you can do that. You may be able to override the arbitrary for that specific case-class instead though.

Dario Abdulrehman

@dabd

I may be using it incorrectly but I attempted to use scalacheck-shapeless to automatically generate data for a sealed trait hierarchy. It turned out that the generators are very generic and not very useful for my purposes. For example a case class with a String field apparently uses Arbitrary.arbString and that is too generic for my application. Is there a way to customise the generators for a field using the library?

Dario Abdulrehman

@dabd

The only way around it I found is to use tagged types and write Arbitrary implicits.

Georgi Krastev

@joroKr21

I guess depending on your taste you could also just import your own implicit Arbitrary[String]

If you don't mind having orphan typeclass instances

Dario Abdulrehman

@dabd

I suppose @edmondo1984 was asking a similar question above

Dario Abdulrehman

@dabd

@joroKr21 and what if your case class has two different fields of type String which need different instances of Arbitrary. I think in this case you have to use tagged types.

Georgi Krastev

@joroKr21

I'm not sure I would have to check

Dario Abdulrehman

@dabd

The implicit mess + tagged types makes it easier to just hand-craft the case class generators.

Georgi Krastev

@joroKr21

yeah if you want customization might be easier to handroll it

you could use https://christopherdavenport.github.io/cats-scalacheck/

with mapN

In theory it would be easy to make it work with LabelledGeneric

And customize your generators based on the field name

But I don't think it exists in scalacheck-shapeless ATM

Akhtiam Sakaev

@asakaev

Hello. I am getting compiler "stackoverflow" when trying to derive generators for scalapb data.

at scala.tools.nsc.typechecker.Implicits$ImplicitSearch.scala$tools$nsc$typechecker$Implicits$ImplicitSearch$$typedImplicit(Implicits.scala:622)
        at scala.tools.nsc.typechecker.Implicits$ImplicitSearch$ImplicitComputation.rankImplicits(Implicits.scala:1213)
        at scala.tools.nsc.typechecker.Implicits$ImplicitSearch$ImplicitComputation.findBest(Implicits.scala:1248)
        at scala.tools.nsc.typechecker.Implicits$ImplicitSearch.searchImplicit(Implicits.scala:1305)
        at scala.tools.nsc.typechecker.Implicits$ImplicitSearch.bestImplicit(Implicits.scala:1730)
        at scala.tools.nsc.typechecker.Implicits.inferImplicit1(Implicits.scala:112)
        at scala.tools.nsc.typechecker.Implicits.inferImplicit(Implicits.scala:91)
        at scala.tools.nsc.typechecker.Implicits.inferImplicit$(Implicits.scala:88)
        at scala.tools.nsc.Global$$anon$5.inferImplicit(Global.scala:483)
        at scala.tools.nsc.typechecker.Implicits.$anonfun$inferImplicit$1(Implicits.scala:144)
        at scala.tools.nsc.typechecker.Implicits.inferImplicit(Implicits.scala:144)
        at scala.tools.nsc.typechecker.Implicits.inferImplicit$(Implicits.scala:142)
        at scala.tools.nsc.Global$$anon$5.inferImplicit(Global.scala:483)
        at scala.reflect.macros.contexts.Typers.inferImplicitValue(Typers.scala:56)
        at scala.reflect.macros.contexts.Typers.inferImplicitValue$(Typers.scala:54)
        at scala.reflect.macros.contexts.Context.inferImplicitValue(Context.scala:18)
        at scala.reflect.macros.contexts.Context.inferImplicitValue(Context.scala:18)
        at shapeless.LazyMacros$DerivationContext$State$.resolveInstance(lazy.scala:303)
        at shapeless.LazyMacros$DerivationContext.resolve0(lazy.scala:421)
        at shapeless.LazyMacros$DerivationContext.$anonfun$deriveLowPriority$1(lazy.scala:449)
        at scala.Option.flatMap(Option.scala:283)
        at shapeless.LazyMacros$DerivationContext.helper$2(lazy.scala:446)
        at shapeless.LazyMacros$DerivationContext.deriveLowPriority(lazy.scala:483)
        at shapeless.LazyMacros$DerivationContext.derive(lazy.scala:494)
        at shapeless.LazyMacros$DerivationContext$State$.deriveInstance(lazy.scala:327)
        at shapeless.LazyMacrosCompat.deriveInstance(lazymacros.scala:50)
        at shapeless.LazyMacrosCompat.deriveInstance$(lazymacros.scala:33)
        at shapeless.LazyMacros$.deriveInstance(lazy.scala:573)
        at shapeless.LazyMacros.mkImpl(lazy.scala:216)
        at shapeless.LazyMacros.mkStrictImpl(lazy.scala:209)
        at shapeless.LazyMacrosRef.mkStrictImpl(lazyref.scala:39)
        at scala.reflect.macros.runtime.JavaReflectionRuntimes$JavaReflectionResolvers.$anonfun$resolveJavaReflectionRuntime$5(JavaReflectionRuntimes.scala:45)

Can I do something with this or I have big nested type that can not be derived?

Georgi Krastev

@joroKr21

You could try bumping up the stack

I usually go for -Xss2m

Akhtiam Sakaev

@asakaev

@joroKr21 4m already, doesn't helps 🤷‍♂️

Georgi Krastev

@joroKr21

But do you see a loop in the stack trace? From the part you shared I don't.

Also how big is this nested type?

One thing you might try is break it up, i.e. derive generators for the inner types first and then for the outer ones.

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