Method unary_~ in class must be called with () argument

[cacapouh]

Compiler version

3.2.2

Minimized code

@main
def main() = {
  class DoubleOps(d: Double) {
    def unary_~(): Double = scala.math.ceil(d)
  }
  implicit def doubleOps(d: Double): DoubleOps = new DoubleOps(
    d
  )

  println {
    ~(0.5) // compilation error
  }
}

Output

sbt:scala3playground> compile;
[info] compiling 1 Scala source to /Users/tobita_yoshiki/work/tmp/scala3playground/target/scala-3.2.2/classes ...
[error] -- [E100] Syntax Error: /Users/tobita_yoshiki/work/tmp/scala3playground/src/main/scala/Main.scala:11:4 
[error] 11 |    ~(0.5)
[error]    |    ^^^^^^
[error]    |    method unary_~ in class DoubleOps must be called with () argument
[error]    |
[error]    | longer explanation available when compiling with `-explain`
[warn] there was 1 feature warning; re-run with -feature for details
[warn] one warning found
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 0 s, completed 2023/04/21 23:43:07

Expectation

The compilation is successful and the following output is expected to be printed to standard output:

1.0

It has been confirmed to work with Scala 2.13.10.

// Scala 2.13.10
object Main extends App {
  class DoubleOps(d: Double) {
    def unary_~(): Double = scala.math.ceil(d)
  }

  implicit def doubleOps(d: Double): DoubleOps = new DoubleOps(
    d
  )

  println {
    ~(0.5) // 1.0
  }
}

[sjrd]

unary_~ must be declared as

def unary_~ : Double = ...

without ().

[cacapouh]

I see, it seems it was not a bug after all. I will close this issue.

[He-Pin]

But the error message can be improved

[cacapouh]

But the error message can be improved

I will create an Issue to improve the error message.

[som-snytt]

It has been confirmed to work with Scala 2.13.10.

This is a "lie". It is deprecated and errors under -Xsource:3.

➜  scala -Xsource:3
Welcome to Scala 2.13.10 (OpenJDK 64-Bit Server VM, Java 19).
Type in expressions for evaluation. Or try :help.

scala>   class DoubleOps(d: Double) {
     |     def unary_~(): Double = scala.math.ceil(d)
           def unary_~(): Double = scala.math.ceil(d)
               ^
On line 2: error: unary prefix operator definition with empty parameter list is unsupported: instead, remove () to declare as `def unary_~ : Double = scala.math.ceil(d)`

The "real problem" for Scala 3 is that the warning is not reported because of the error.

This is an old "philosophical" issue, that first you resolve the errors and then you resolve the warnings.

Of course, the compiler ought to emit no warnings. The compiler should emit errors, and the linter or IDE should emit warnings (or "suggestions") that might help resolve the errors.