Valhalla EG notes Jan 16, 2019

John Rose john.r.rose at
Tue Jan 29 23:29:01 UTC 2019

On Jan 29, 2019, at 11:10 AM, Remi Forax <forax at> wrote:
> currently the result of the expression "new Object()" is a reference type, so it should be a RefObject, but we have created an Object not a RefObject,
> so it's at best weird. 

I'd like to rationalize this in two steps.

First, allow `new I(x…)` where `I` is an interface,
to be treated as shorthand for `I.F(x…)` where
the method `F` is somehow declared by `I` as
its canonical factory.  I'm thinking `List.of` is
a good one.  (Maybe also extend this rule to classes
with non-public constructors.)

Second, since `Object` is an honorary interface,
change the meaning of `new Object()` to be
`Object.newReference()` (or some such), by
having `Object` declare `newReference` (of
no arguments) as its canonical factory.

Moving `new` statements to factories is coherent,
also, with changing the translation strategy for Java
to deprecate the new/init dance outside of the class
being constructed, and eventually make it illegal in
bytecode outside of the nest of the class being made.
In other words, if I could go back in a time machine
and rewrite the translation strategy, I'd insist that
each class (or the JVM itself) would define a canonical
factory for each constructor of that class, and require
all other classes to allocate via the canonical factory.
The new/init dance would be legal inside the class
but nowhere else.  That attack surface has been a
painful one.  And value types have to use factories
from the get-go, so we've got to figure it out sooner
or later.  The name of the canonical factory can be,
in fact, fixed as '<init>'.

— John

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