On 04/20/2015 11:06 AM, Paul Sandoz wrote:
Hi Peter,
We did consider supporting field and method literals in 9, leveraging the same
syntax as for method references combined with target typing. But, we have
currently concluded it would be best to punt it to post-9.
As a result there is currently no compelling need to support VarHandles in the
constant pool, which, while not particular hard AFAICT (famous last words!), is
a welcome reduction in work.
Paul.
You don't even need to have VarHandle in the constant pool,
once you have invokedynamic, you can create any constant you want at
runtime,
MethodHandles are in the constant pool only because you need it to
reference the bootstrap method of an invokedynamic, you need it to
bootstrap invokedynamic if you prefer.
That's not fully true because we may also want to have a way to
represent constant fields in annotation.
This give me an idea, invokedynamic should be used to specify the
constant values in annotation.
It will be extensible for the JDK and any (dynamic) languages that have
a more powerful annotation mechanism
(Groovy anyone?) will be able to leverage that.
At runtime, an annotation will still be a proxy but instead of using
java.lang.reflect.Proxy,
it should use the Proxy2 API [1] :)
Rémi
[1] https://github.com/forax/proxy2
On Apr 20, 2015, at 10:41 AM, Peter Levart <peter.lev...@gmail.com> wrote:
The thing that pushed us over the edge is that value types are coming. With value
types, one can create type-safe, zero-cost, specialized wrappers for
{Static,Instance,Array,Native}VarHandle<T> that wrap an underlying VH; because
these wrappers can be values, they can provide type safety with no indirection or
footprint costs. So it seemed better to provide a simple, clean, low-level API now
that doesn’t make any assumptions, let the early adopters (mostly us) deal with the
fact that type safety comes at runtime (just as with MHs), and later provide a clean
set of value wrappers on top of it.
This seems like a good plan for post-JDK9 times. But I still miss one thing in
this picture - the syntax. If purely API approach is taken, then we will still
be using Strings to identify fields and do the caching of VarHandles ourselves.
Are there any plans for specifying syntax for constant [Method|Var] handles in
Java or is this being reserved for post-JDK9 times where the syntax will be
used to produce type-safe wrappers (similar to approach taken with
MethodHandles vs. Lambdas)?
Regards, Peter
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