I think we're on the same page regarding specialized <clinit>.
- The JVM will be handed multiple <clinit> partial methods, and the
specializer will take care of selecting the appropriate <clinit> for
each specialization.
- The erased <clinit> will contain the non-specialized static
initialization code, which ensures that it only runs once.
- The erased <clinit> will always run before the first specialization
<clinit>.
- The Java syntax is still up for discussion.
> I think this is mostly a matter of coming up with the right syntax,
which makes it clear that statics can be per-class or
per-specialization. There are a whole pile of related
specialization-related syntax issues, I'll try to get them all in one
place.
I don't think the problem will be to make it clear that statics can be
per-class or per-specialization, but rather why some parameterizations
(which to the user are synonymous with specializations) don't appear
to have specialized statics. Do we want to put erasure in the face of
users like this? It seems better to let the users deal purely with
parameterizations, and we let specialization and erasure be
implementation details.
--
Bjørn Vårdal
----- Original message -----
From: Brian Goetz <[email protected]>
To: Bjorn B Vardal/Ottawa/IBM@IBMCA,
[email protected]
Cc:
Subject: Re: Classes, specializations, and statics
Date: Thu, Feb 18, 2016 7:55 PM
Based on the example above, I think we need to be more explicit
about how the <clinit> method is handled.
There are really two different sets of statics that need to be
handled by the class initialization:
A) common statics (shared across all instantiations)
B) specialized statics
In addition to the statics, there is also common (and maybe
specialized?) code that is run as part of <clinit>.
There is a reasonable model to collapse these back into one
concept; treat "common statics" as specialized statics on the
all-erased parameterization, with a <where> clause that restricts
them to that parameterization. Not clear whether we actually want
to represent it that way or not, but its a useful mental model
that doesn't require the creation of a third thing. (Since
Class[Foo] and ParamType[Foo,erased*] describe the same class,
this is also fully binary compatible with existing classes.)
Which means we can do a similar thing with <clinit>, if we want.
I'll wave my hands because we've not yet talked much about
conditional members, but it basically looks like this:
<where T*=erased*>
<init>() { /* common static init code */
/* specializable init code */ }
<init>() { /* specializable init code */ }
Or not.
Where will the initialization code for both kinds of statics be?
The existing <clinit> method?
We have two choices:
- have a new <sclinit> block that gets run once per
specialization, and keep <clinit>
- merge the two as above, exploiting planned support for
conditional members
Either way, as you say, we have to ensure that the common init
runs exactly once.
When using *static, are we only discussing {get,put}? Or is this
also proposing invokestatic changes to allow specialized static
methods?
Methods too.
All of the technical details aside, is this something we really
want to expose to the users? They're going to have a hard time
understanding why Foo<int> (or Foo<ValueType) gets specialized
statics while Foo<String> & Foo<Bar> share the erased version.
I think this is mostly a matter of coming up with the right
syntax, which makes it clear that statics can be per-class or
per-specialization. There are a whole pile of related
specialization-related syntax issues, I'll try to get them all in
one place.
