> On Jul 7, 2017, at 8:56 AM, Maurizio Cimadamore
> <[email protected]> wrote:
>
> Hi,
> over the last few weeks we've been exploring the twisted relationship between
> patterns and nulls. This document:
>
> http://cr.openjdk.java.net/~mcimadamore/nulls-patterns.html
>
> provides some (hopefully helpful) insights into what the design space looks
> like.
>
> tl;dr;
>
> Looks like trying to force the same rule on all patterns, regardless of where
> they appear, leads to problems. Distinguishing between toplevel and nested
> patterns provides a good basis to handle null in a more predictable/flexible
> fashion.
>
Nice write-up! But there is one other direction that it does not seem to
explore: extending the type system to have explicitly non-null reference types
(an old idea, but perhaps the correct solution for patterns).
String can be String or null
String! cannot be null
if (o matches String! x) { … o cannot be null here … }
if (o matches LinkedList(Object! head, LinkedList tail)) { … head cannot be
null here … }
Not sure it’s where we want to go, but at least it should be explicitly
considered, if only to explicitly reject it.
—Guy
