Nullability syntax

[Jonathan F]

 It seems the syntax of nullable types is extra-important for its
usability, so here’s an idea which perhaps the EG hasn’t considered. Remi
has mentioned a 2-states model? - maybe this is different:

- Assume there’s some way (any way) to specify default nullability within
some scope: to set either that String means String!, or that it means
String?. If you don’t specify anything, as now, String means unspecified
null.

- Then: if you set default nullability to ! , you’re allowed to write
String or String? but not String! (i.e. you can’t belabour the
non-nullability of a particular String)

- Likewise if you set default nullability to ? , you’re allowed to write
String or String! but not String?. Or maybe we don’t even need this default.

- (I think…) if you don’t set a default so it's 'unspecified null’ (as
now), then neither String? nor String! is allowed: they force you to set a
default.


The point of this is:

- There’s clarity in only being allowed to use 1 type of punctuation in a
class. And seeing it tells you there’s a default.

- If you see ? or ! in a sample of code you’ll know what a bare String
means: ’the opposite'.

- Pasting raw code between two classes with different nullability will
often give compile errors from mixed punctuation (unless your IDE adjusts
the code, which hopefully IDEs will).

- This fits with simple ways to convert an existing class to being
null-aware: set the default to !, so existing types are reinterpreted as
null-restricted, then fix errors by adding ? piecemeal. But if you want to
make minimal changes you may want to set the default to ? instead, then add
! piecemeal; or again maybe we don’t need that default - even simpler.

As for actually using ‘unspecified null’ (which I hope will be rare in
null-aware code) - maybe String* or even String!? is OK.

I hope that (or something like it) makes sense.

Jonathan

Jonathan Finn
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/valhalla-dev/attachments/20250410/d7dc4fa2/attachment-0001.htm>