Implement Show typeclass about hamsters

[oraclewalid]

To use the macro from external project, I think user must add
addCompilerPlugin("org.scalameta" % "paradise" % "3.0.0-M10" cross CrossVersion.full) to build.sbt, then external projet can call ShowMacro

[dgouyette]

+1

[dgouyette]

No need to use macro for that. We juste have to provide implicit for primitive, no ?

[loicdescotte]

How do you get the field names (name, age) without reflection?
The goal is to avoid to pass it explicitly

[oraclewalid]

If you want show filed names, I think use of macro is mandatory

[dgouyette]

you don't want something like ? : https://github.com/typelevel/cats/blob/master/tests/src/test/scala/cats/tests/ShowTests.scala
Or you want the macro to do something like public String toString() { return new ToStringBuilder(this, ToStringStyle.MULTI_LINE_STYLE).append("Name", name).append("Age", age).toString(); }
Does it work with case class, class, sealed trait ?

[loicdescotte]

I was thinking of something very simple, to help debugging for example, with automatic generation like this : https://github.com/milessabin/kittens/blob/master/README.md#derive-show

But if a macro can generate automatically a default implicit, then I guess it would easy to pass a custom implicit too.

[dgouyette]

Ok, i take the point

[loicdescotte]

Great!
I have a draft without the macro, I'll try to clean it/put it in a branch before tonight.

[loicdescotte]

Here is the branch : https://github.com/scala-hamsters/hamsters/tree/show

Edit : I've added a test case for deep case class formatting

[dgouyette]

i made a pull request a few minutes ago.
it doesn't take case class with companion objects and it doesn't take other primitives than String and Int

[loicdescotte]

Thanks, really great! 👍 Le sam. 14 oct. 2017 à 08:45, GOUYETTE Damien <[email protected]> a écrit :

…

i made a pull request a few minutes ago. it doesn't take case class with companion objects and it doesn't take other primitives than String and Int — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#34 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAm8xohjE3hg1dd-x3LVfds_6hKBwHeYks5ssFiUgaJpZM4PcjzA> .

[loicdescotte]

For future improvements, do you think it would be possible to generate an implicit via the macro rather than annotating the case class?

Something like :

case class Person(name: String, age: Int)
implicit val personShowable = Show.format[Person]
val p = Person("bob", 40)
Show.show(p) // takes personShowable as implicit

For example it works this way with Play JSON :

implicit val personJsonFormat = Json.format[Person]
val jsonString = Json.toJson(p) // takes personJsonFormat  as implicit

The main reason about this is that people usually don't want to annotate their case class, and I think the macro is not usable from the hamsters jar when it's compiled, am I wrong?

[dgouyette]

It seems to be possible with Scala meta 2.0.0-M1. But we'll lose scala 2.11 support (see scalacenter/macros#1) .

Exemple : https://github.com/scalamacros/sbt-example-newstyle.

Maybe we could do something like :

import ShowableSyntax._
val p = Person("bob", 40)
println(p.show)

Which one do you prefer ?
I would like to give a try to def macros

[loicdescotte]

@dgouyette it seems to work in Play even with scala 2.10, is it a different use case?
About the syntax yes I like it, I think it would be nice to have Show.show and p.show (via syntax implicit class).
@oraclewalid macros are not included in the jar so it would not work.

[loicdescotte]

Remaining tasks for a first version of Show (using show branch) :

• make the macro usable from the tests (should work for any client of the lib too)
• move the case classes outside the Show.scala file (move to the right test)
• move show tests at the same level as other tests