In the following code (mentioned in another answer, but leads to a separate question), a so-called evidence parameter is used to indicate to the compiler that the A parameter is of type string via a context bound.
case class Foo[A](a:A) { // 'A' can be substituted with any type
// type constraint ensures type A
def getStringLength(implicit evidence: A =:= String) = a.length
}
But, why not simply define the class without a type parameter at all? I mean, if you parameterize the type being used, then you want a generic class; otherwise, why not just omit the type parameter as in the following?
case class Foo(a: String) {
def getStringLength(implicit evidence: A) = a.length
}
What is an example where the context bound leads to an advantage?
