CODEWITHSUNDEEP
scalafunctional-programming
PawelN
PawelN

Reputation: 848

Why Scala implement andThen function only for Function1

Why Scala has implementation of method andThen only for Function1 (which takes only one parameter). I don't see any reason why rest of functions does not have such method.

Below we have legal code which will compile:

val firstFunction: String => String = ???
val secondFunction: String => String = ???
firstFunction.andThen(secondFunction)

but this will not compile:

val firstFunction: (String,String) => String = ???
val secondFunction: String => String = ???
firstFunction.andThen(secondFunction)

Upvotes: 3

Views: 304

Answers (2)

Eduardo Pareja Tobes
Eduardo Pareja Tobes

Reputation: 3120

I guess you would want andThen to return a Function2 in your firstFunction.andThen(secondFunction) example.

You can easily add this to Function2 (or any other FunctionN):

implicit final
class Function2MulticategoryOps[A,B,C](val f: (A,B) => C) extends AnyVal {

  def andThen[X](g: C => X): (A,B) => X =
    (a,b) => g(f(a,b))
}

tupled by itself won't help much there: you also need something like untupled:

// note the awful syntax for functions with domain a tuple
implicit final
class Untuple[A,B,C](val f: ((A,B)) => C) extends AnyVal {

  def untupled: (A,B) => C =
    (a,b) => f((a,b))
}

As to why the FunctionN classes lack these methods, I don't know; surely someone would chime in with something related with performance.

PS If you ask me, I think life would be easier if there will be no FunctionN classes, and functions of several arguments would simply be functions with domain a product type; all this FunctionN business is just a convoluted and partial implementation of the representable multicategory coming from a category with products.

Upvotes: 1

Yuval Itzchakov
Yuval Itzchakov

Reputation: 149538

I don't see any reason why rest of functions does not have such method.

Because it is trivial to transform a Function2[String, String, String] to a Function1[(String, String), String], using Function.tupled:

firstFunction.tupled andThen secondFunction

This will work for functions of any arity.

Upvotes: 5

Related Questions