`Tuple1SemigroupalOps` methods have different names from other `TupleNSemigroupalOps` classes about cats HOT 3 OPEN

I've just realized there's even a broader issue with Tuple1: depending on imports used, the map method for Tuple1 can change its semantic dramatically. Check this out:

import cats.syntax.functor._

scala> val t1 = Tuple1(List("A", "B"))
val t1: (List[String],) = (List(A, B),)

scala> t1.map(s => s"$s!")
val res0: (String,) = (List(A, B)!,)

However, if I use another syntax import:

scala> import cats.syntax.apply._

scala> val t1 = Tuple1(List("A", "B"))
val t1: (List[String],) = (List(A, B),)

scala> t1.map(s => s"$s!")
val res0: List[String] = List(A!, B!)

I.e. the same t1.map(s => s"$s!") call for exactly the same Tuple1(List("A", "B")) value works differently and produces results of different types depending on whether import cats.syntax.functor._ or import cats.syntax.apply._ is used.

I think it is somewhat confusing.

from cats.

Although I don't know for sure the reasoning behind such naming conventions, my guess is that despite Tuple1SemigroupalOps name its methods do not require the Semigroupal typeclass actually – but only Functor, Traverse, etc. Whereas all the other TupleNSemigrioupalOps methods for N >= 2 do require the Semigroupal typeclass.

In other words, we can assume that Tuple1[N] is isomorphic to Id[N] and therefore do not need mapN semantic.

from cats.

mapN on a Tuple1 in isolation is kind of silly - but so is any use of Tuple1 in isolation - as you say, Tuple1[N] is isomorphic to Id[N]. The only real reason for having Tuple1 (and therefore Tuple1SemigroupalOps) at all is to operate consistently on tuples of all sizes - if you have to special-case Tuple1 anyway then you might as well just operate on the value inside.

from cats.