Feature Request: toLabelledProduct

[schlichtanders]

Dear shapeless team,

having toProduct support for unnamed Hlist, it seems a natural request to have method like toLabelledProduct for named Hlist of records (like automatically derived by LabelledGeneric )

any plans on implementing this?

[milessabin]

Are you referring to the toProduct syntax for function types that's defined in shapeless/syntax/std/functions.scala?

[schlichtanders]

yes, thanks for clarification.

I am coming from a Python background and there I have the star * and doublestar ** tools for passing lists and dictionaries as function arguments respectively.

With shapeless it seems we can already support * via myfunction.toProduct(hlist) and using plain HLists
It would be great to support named arguments like in ** similarly by something like myfunction.toLabelledProduct(labelledHList)

[milessabin]

Gotcha.

Scala function types don't encode the names of their arguments, so unfortunately what you ask isn't possible. Scala methods do, but they have the limitation that they're not first class. If that isn't a problem for you, then you might be able to make some headway with RecordArgs.

[schlichtanders]

I see. Yeah that is unfortunate, but if something like this could work with methods, I would love to have it

how could the syntax look like?

[milessabin]

It does work with methods ... see the tests for RecordArgs and FromRecordArgs, or look at some of the uses in other projects :-)

[schlichtanders]

thanks a lot for the pointers!
so it seems you have to extend RecordArgs if you want to build you own custom Records HList methods, but offer "normal" interfaces. Perfect

However for interfacing already defined normal functions with FromRecordArgs it seems we have to hope that the class is inheritable, or the methods defined on a trait, so that we can create our custom wrapper class Wrapper extends Original with FromRecordArgs

Is there also support for interfacing "normal" methods which are not inheritable in such a manner?

[milessabin]

Is there also support for interfacing "normal" methods which are not inheritable in such a manner?

No there isn't.

[schlichtanders]

thanks a lot

this sounds like a class FromRecordArgsProxy[A](a: A) extends FromRecordArgs would be awesome, which is supposed to wrap a custom object of kind of arbitrary type. With such you could easily access myMethodRecord for any "normal" method.

However to the best of my knowledge such proxies are not well supported currently (haven't found a single satisfiable implementation out there for Scala). If you know about a proxy which could accomplish this, please drop me a line.

[joroKr21]

One could imagine having a toLabelledProduct where you have to pass the labels explicitly.
But I'm not sure how useful that would be.

[joroKr21]

It could also work as a macro when passed a reference to a method or a literal function.