A syntax option (function types versus arrays)

[Neal Gafter]

On Mon, Mar 1, 2010 at 4:58 PM, Joshua Bloch <jjb at google.com> wrote:
> Why do you say we won't be able to express arrays of disjunction types? Is
> there some fundamental reason it's not possible?

No, we can technically add support for anything we want, but if the
syntax can't be used safely in the language, it doesn't make much
sense.  We'd really have to go out of our way to make up a syntax that
is more awkward just to make sure we can express something that we
cannot implement.  What you're proposing is a false orthogonality.  I
understand what 308 did by adding support for annotating types in only
some (but not all) places in the language for no particular technical
reasons but absence of compelling use cases, but in this case we have
sound technical reasons as well.  (If it wasn't clear, disjunction
types are not reifiable).

> If so, then yes, they'd be
> second-class citizens (if we decided to support them). But that's no reason
> to turn function types into second class citizens when we have a choice in
> the matter.

Whether the syntax makes it obvious or not, function types would be
second-class citizens in precisely the way you're complaining about:
there's no correct way to make arrays of them.  We'd not be doing any
favors by pretending otherwise in the syntax.