Question

I’m relying on an old Java API that kinda sucks and loves to throw null pointer exceptions when data is missing. I want to create a subclass that has option type accessors but preserves the old accessors until I decide I need to create safe accessors for them. Is there a good way to create a subclass from a copy of the original object? I’d like to achieve something like the following:

SafeIssue extends Issue {
  def safeMethod: Option[Value] = { //... }
}


val issue = oldapi.getIssue()
val safeIssue = SafeIssue(issue)

//Preserves issue's methods and data if I need them
val unsafeVal = safeIssue.unsafeMethod
val maybeVal  = safeIssue.safeMethod

Answer 1

Why not try an implicit conversion instead? This works better with Java APIs that like to create their own objects. So you would

class SafeIssue(issue: Issue) {
  def original = issue
  def safeFoo = Option(issue.foo)
  // ...  You must write any of these you need
}
implicit def make_issues_safe(issue: Issue) = new SafeIssue(issue)

Then you can–as long as you’ve supplied the method–write things like

val yay = Issue.myStaticFactoryMethodThing.safeFoo.map(x => pleaseNoNull(x))

(You can then decide whether you want to carry SafeIssue or Issue around in your code, and you can always get back the Issue from SafeIssue with the exposed original method (or you could make the issue parameter a val.)