Scala Implicit function within a function call

Question

I've defined a class that has a method in it that is trying to make use of a function with an implicit parameter in it. Unfortunately it's failing to compile

class Test {
    def useImplicit(implicit a: Boolean) = a
    def getAnswer() = if (useImplicit) println("yes") else println("no") 
}

object Preferences {
    implicit val yes = false
    implicit val no = false
}

The problem is that when I go to compile the class to try and test it out I get the error

could not find implicit value for parameter a: Boolean
   def getAnswer() = if (useImplicit) println("yes") else println("no")

I'm not exactly sure what is going on here. The reason for me trying it this way is I am ultimately wanting to overload hashCode and determine at runtime whether I should run my overloaded version or call the parent implementation. If this isn't possible I suppose I could make the class take an implicit

Michael Zajac · Accepted Answer · 2014-12-03 23:37:02Z

1

getAnswer is calling useImplicit, but there is no implicit Boolean within the scope of Test. getAnswer will also require the implicit parameter to work:

def getAnswer(implicit a: Boolean) = if(useImplicit) println("yes") else println("no")

The alternative is making Test require the implicit on instantiation, as you say.

answered Dec 3, 2014 at 23:37

Michael Zajac

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1 Comment

Adam Ritter Over a year ago

The ultimate problem is I'm trying to override a function at runtime. I can't add the parameter to the getAnswer method due to the fact that it would change the method signature and therefor not be executed by the calling code. I just realized I need to use a trait and mix it in at run time when creating the object.

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