Is there a way to control which implicit conversion will be the default used?

问题

Suppose I have this:

class String2(val x:String) {
    def *(times:Int) : String = {
        val builder = new StringBuilder()
        for( i <- 0 until times) {
            builder.append(x)
        }
        builder.toString()
    }
}

now if I add this implicit:

implicit def gimmeString2(y:String) = new String2(y)

I will get a compilation error because stringWrapper also adds this implicit. Is there a way of saying to the compiler \"ignore other implicits, use this\", so that I don\'t have to instantiate a String2 object and work on that?

I admit the example code may not be the most appropriate ( for this question ), but I think it will do.

回答1:

Scala 2.8 added a prioritization system for implicits. It's explained in this SIP on the new Java arrays:

When comparing two different applicable alternatives of an overloaded method or of an implicit, each method gets one point for having more specific arguments, and another point for being defined in a proper subclass. An alternative “wins” over another if it gets a greater number of points in these two comparisons

concluding that if alternatives have identical argument types, the one which is defined in a subclass wins. Hence I believe that you could declare implicits as follows:

trait LowPriorityImplicits {
  //lower priority conversions
}

object HighPriorityImplicits extends LowPriorityImplicits {
  //higher-order ones here
}

来源：https://stackoverflow.com/questions/1886953/is-there-a-way-to-control-which-implicit-conversion-will-be-the-default-used