How can Scala explicitly resolve the ambiguity of overloaded methods?

Probably, Scala cannot invoke the setDefault(Object value) method.

With dotty (Scala 3.x), it may be possible in some way (?).
https://github.com/lampepfl/dotty/issues/5792

For the time being, I can think of about three compromises.
(I excluded how to call in reflection because it is written in the questionnaire.)

Compromise 1: Consider using another library

• https://stackoverflow.com/questions/2315912/best-way-to-parse-command-line-parameters
• https://stackoverflow.com/questions/8112879/scala-command-line-parser-with-subcommand-support

Compromise 2: Call the setDefault(E...value) method

With this method, I think I can call you with the following code.

arg.setDefault(Seq("foo"):_*)

However, I think the default values displayed in Help will be as follows:
(There will be extra [])

 (default: [foo])

Compromise 3: Write helper class in Java and use it in Scala

The method used by argparse4j's Scala wrapper mdekstrand/argparse4s, under src/main/java

public static void setDefault (Argument arg, Object dft)

Define a helper class with the method

/src/main/java/net/elehack/argparse4s/ArgConfig.java

package net.elehack.argparse4s;

import net.sourceforce.argparse4j.inf.Argument;

classArgConfig {
    public static void setDefault (Argument arg, Object dft) {
        arg.setDefault (dft);
    }
}

*It seems that this Scala wrapper library itself has not been maintained as of 2019.

Is there a general way to avoid ambiguity?"That's not clear, but with this pattern, ""Would you like to take the type argument or not?""""Because of the difference, I think it is possible to call the variable length argument (although it is not a direct answer to the question) by specifying the type argument.

scala>net.sourceforce.argparse4j.ArgumentParsers.newFor("a").buildArgument().addArgument("b").setDefault("c")
<console>:14:error:ambiguous reference to overloaded definition,
both method setDefault into trace Argument of type [E] (x$1:E*) net.sourceforce.argparse4j.inf.Argument
and method setDefault into trace Argument of type (x$1:Any) net.sourceforce.argparse4j.inf.Argument
match argument types (String)
       net.sourceforce.argparse4j.ArgumentParsers.newFor("a").build().addArgument("b").setDefault("c")
                                                                                       ^

scala>net.sourceforce.argparse4j.ArgumentParsers.newFor("a").build().addArgument("b").setDefault [String]("c")
res0: net.sourceforce.argparse4j.inf.Argument=net.sourceforce.argparse4j.internal.ArgumentImpl @736cb954

Also, even if you call it by reflection, if you use structural subtyping on purpose as shown below, it will be a little shorter and more convenient.

.asInstanceOf[{defaultDefault(x:AnyRef)}].setDefault("c")

Looking at it, it seems that there is no explicit solution in Scala's description.
In the argparse4j case, we use the return value as a method chain, so we made use of Structural Subtyping in the implicit class.

implicit class_Argument(arg:Argument){
  defaultDefault2(value:Any): Argument={//←The name is appropriate, but
    import scala.language.reflectiveCalls
    arg.asInstanceOf [{defaultDefault(value:Object):Argument}:].setDefault(value)
  }
}