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Remove unused parameters from methods #1867

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Remove unused parameters from methods #1867

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505d286
Remove unused parameters from methods
Alistair-Johnson Aug 27, 2017
d6f7052
Revert change to MonadError
Alistair-Johnson Aug 27, 2017
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2 changes: 1 addition & 1 deletion core/src/main/scala/cats/data/Validated.scala
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Expand Up @@ -278,7 +278,7 @@ object Validated extends ValidatedInstances with ValidatedFunctions{
* Uses the [[http://typelevel.org/cats/guidelines.html#partially-applied-type-params Partially Applied Type Params technique]] for ergonomics.
*/
private[data] final class CatchOnlyPartiallyApplied[T](val dummy: Boolean = true ) extends AnyVal{
def apply[A](f: => A)(implicit T: ClassTag[T], NT: NotNull[T]): Validated[T, A] =
def apply[A](f: => A)(implicit T: ClassTag[T]): Validated[T, A] =
try {
valid(f)
} catch {
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2 changes: 1 addition & 1 deletion core/src/main/scala/cats/syntax/either.scala
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Expand Up @@ -24,7 +24,7 @@ object EitherSyntax {
* Uses the [[http://typelevel.org/cats/guidelines.html#partially-applied-type-params Partially Applied Type Params technique]] for ergonomics.
*/
private[syntax] final class CatchOnlyPartiallyApplied[T](val dummy: Boolean = true ) extends AnyVal {
def apply[A](f: => A)(implicit CT: ClassTag[T], NT: NotNull[T]): Either[T, A] =
def apply[A](f: => A)(implicit CT: ClassTag[T]): Either[T, A] =
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While the NT parameter isn't referenced at runtime, it serves an important compile-time role. Consider that you wanted to do something like the following:

scala> Either.catchOnly[NumberFormatException]("foo".toInt)
res2: Either[NumberFormatException,Int] = Left(java.lang.NumberFormatException: For input string: "foo")

If you forget to add the type parameter before this PR you get a compile-time error:

scala> Either.catchOnly("foo".toInt)
<console>:18: error: ambiguous implicit values:
 both method If you are seeing this, you probably need to add an explicit type parameter somewhere, because Null is being inferred. in object NotNull of type => cats.NotNull[Null]
 and method catsAmbiguousNotNullNull2 in object NotNull of type => cats.NotNull[Null]
 match expected type cats.NotNull[Null]
       Either.catchOnly("foo".toInt)

However, with this PR you get a runtime error because Null is inferred as the type parameter:

scala> Either.catchOnly("foo".toInt)
java.lang.NumberFormatException: For input string: "foo"
  at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
  at java.lang.Integer.parseInt(Integer.java:580)
  at java.lang.Integer.parseInt(Integer.java:615)
  at scala.collection.immutable.StringLike.toInt(StringLike.scala:301)
  at scala.collection.immutable.StringLike.toInt$(StringLike.scala:301)
  at scala.collection.immutable.StringOps.toInt(StringOps.scala:29)
  at .$anonfun$res0$1(<console>:15)
  at scala.runtime.java8.JFunction0$mcI$sp.apply(JFunction0$mcI$sp.java:12)
  at cats.syntax.EitherSyntax$CatchOnlyPartiallyApplied$.apply$extension(either.scala:29)
  ... 39 elided

I think that the correct change to make here is to document why this NotNull parameter exists. The same goes for the Validated case.

try {
Right(f)
} catch {
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2 changes: 1 addition & 1 deletion core/src/main/scala/cats/syntax/partialOrder.scala
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Expand Up @@ -8,7 +8,7 @@ trait PartialOrderSyntax extends EqSyntax {
new PartialOrderOps[A](a)
}

final class PartialOrderOps[A](lhs: A)(implicit A: PartialOrder[A]) {
final class PartialOrderOps[A](lhs: A) {
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Can someone who knows machinist better than I do weigh in on whether this change is fine (I suspect so, but I want to make sure). cc @non @johnynek

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I have no idea about the macro expansion in machinist.

I am not sure that is what is going on here anyway. I think it may be to prevent this class from being allocated without a PartialOrder.

We could I'm not sure if this is even tested sadly.

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This seems no longer relevant, since macros have been now removed in preparation for Dotty.

def >(rhs: A): Boolean = macro Ops.binop[A, Boolean]
def >=(rhs: A): Boolean = macro Ops.binop[A, Boolean]
def <(rhs: A): Boolean = macro Ops.binop[A, Boolean]
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