I created a function like this:

def doit(implicit f: => Int) = i * 2

Of course in my actual program "doit" actually does something and only evaluates f occasionally.

The f parameter is implicit because I want callers to be able to use an implicit default value when they know that f will never actually be evaluated:

implicit val default = 0

Unfortunately there seems to be no way to create a val, var, or def in such a way that Scala will choose it as the implicit argument to doit. I tried the following:

implicit def default = 0
implicit val default = { () => 0 }
implicit val default: => Int = 0

Of course the third one doesn't even compile.

If the compiler allows the creation of an implicit by-name parameter, then it should be willing to select an implicit argument for it. If not, then it should be illegal to create the implicit by-name parameter in the first place.