diff options
| -rw-r--r-- | src/dotty/tools/dotc/parsing/Parsers.scala | 2 | ||||
| -rw-r--r-- | src/dotty/tools/dotc/reporting/diagnostic/messages.scala | 24 |
2 files changed, 25 insertions, 1 deletions
diff --git a/src/dotty/tools/dotc/parsing/Parsers.scala b/src/dotty/tools/dotc/parsing/Parsers.scala index 8fc99f072..6871916dd 100644 --- a/src/dotty/tools/dotc/parsing/Parsers.scala +++ b/src/dotty/tools/dotc/parsing/Parsers.scala @@ -692,7 +692,7 @@ object Parsers { else { for (t <- ts) if (t.isInstanceOf[ByNameTypeTree]) - syntaxError("no by-name parameter type allowed here", t.pos) + syntaxError(ByNameParameterNotSupported()) val tuple = atPos(start) { makeTupleOrParens(ts) } infixTypeRest(refinedTypeRest(withTypeRest(simpleTypeRest(tuple)))) } diff --git a/src/dotty/tools/dotc/reporting/diagnostic/messages.scala b/src/dotty/tools/dotc/reporting/diagnostic/messages.scala index b0ce5b132..f76512bc7 100644 --- a/src/dotty/tools/dotc/reporting/diagnostic/messages.scala +++ b/src/dotty/tools/dotc/reporting/diagnostic/messages.scala @@ -581,4 +581,28 @@ object messages { } } + + case class ByNameParameterNotSupported()(implicit ctx: Context) extends Message(21) { + val kind = "Syntax" + + val msg = "By-name parameter type not allowed here." + + val explanation = + hl"""|By-name parameters act like functions that are only evaluated when referenced, + |allowing for lazy evaluation of a parameter. + | + |An example of using a by-name parameter would look like: + |${"def func(f: => Boolean) = f // 'f' is evaluated when referenced within the function"} + | + |An example of the syntax of passing an actual function as a parameter: + |${"def func(f: (Boolean => Boolean)) = f(true)"} + | + |or: + | + |${"def func(f: Boolean => Boolean) = f(true)"} + | + |And the usage could be as such: + |${"func(bool => // do something...)"} + |""".stripMargin + } } |