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Add error message - _* syntax - Parsers.scala:1082 #1635

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Merged
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Nov 3, 2016
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Add error message - _* syntax - Parsers.scala:1082 #1635

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3 changes: 2 additions & 1 deletion src/dotty/tools/dotc/parsing/Parsers.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1079,7 +1079,8 @@ object Parsers {
if (in.token != RPAREN) syntaxError("`_*' can be used only for last argument", uscoreStart)
Typed(t, atPos(uscoreStart) { Ident(tpnme.WILDCARD_STAR) })
} else {
syntaxErrorOrIncomplete("`*' expected"); t
syntaxErrorOrIncomplete(IncorrectRepeatedParameterSyntax())
t
}
case AT if location != Location.InPattern =>
(t /: annotations())(Annotated)
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27 changes: 26 additions & 1 deletion src/dotty/tools/dotc/reporting/diagnostic/messages.scala
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Expand Up @@ -580,7 +580,6 @@ object messages {
}
}


case class ByNameParameterNotSupported()(implicit ctx: Context)
extends Message(21) {
val kind = "Syntax"
Expand Down Expand Up @@ -729,4 +728,30 @@ object messages {
| - auxiliary constructors specify the implicit value
|"""
}

case class IncorrectRepeatedParameterSyntax()(implicit ctx: Context) extends Message(27) {
val kind = "Syntax"
val msg = "'*' expected"
val explanation =
hl"""|Expected * in '_*' operator.
|
|The '_*' operator can be used to supply a sequence-based argument
|to a method with a variable-length or repeated parameter. It is used
|to expand the sequence to a variable number of arguments, such that:
|func(args: _*) would expand to func(arg1, arg2 ... argN).
|
|Below is an example of how a method with a variable-length
|parameter can be declared and used.
|
|Squares the arguments of a variable-length parameter:
|${"def square(args: Int*) = args.map(a => a * a)"}
|
|Usage:
|${"square(1, 2, 3) // res0: List[Int] = List(1, 4, 9)"}
|
|Secondary Usage with '_*':
|${"val ints = List(2, 3, 4) // ints: List[Int] = List(2, 3, 4)"}
|${"square(ints: _*) // res1: List[Int] = List(4, 9, 16)"}
|""".stripMargin
}
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@felixmulder felixmulder Oct 28, 2016

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This can also happen in:

case class Foo(i: Int*)

(null: Foo) match {
  case Foo(i: _) => // ...
}

And providing func with arguments could also be done like: func(1, 2, 3) right? Basically I think your explanation is good, but try to explain what the _* construct does :)

}