Proposal: Improved Type Inference for Generic Instance Creation
Joseph D. Darcy
Joe.Darcy at Sun.COM
Sat Feb 28 00:02:29 PST 2009
Jeremy Manson wrote:
> Hey Neal,
> I think you might have missed where I asked for an example where G1
> and G2 might have different numbers of type parameters or they might
> have corresponding parameters in a different order. I'm probably
> missing a very obvious example, and I'm sure you have an example in
> On Fri, Feb 27, 2009 at 11:33 PM, Neal Gafter <neal at gafter.com> wrote:
>> Adding conversions doesn't make type inference work. Each conversion
>> that you want to affect type inference has to be accommodated
>> specifically in the type inference algorithm.
> I wasn't suggesting that adding conversions would make type inference
> work. I was suggesting that the conversion could be done in place of
> the type inference.
>> I disagree with your suggestion that this should fail:
>> List<?> list = new ArrayList<>(); // should fail
>> The equivalent code using static factories works just fine. It isn't
>> clear why this feature should behave differently, or what part of your
>> specification makes it fail.
> Basically, because I specifically disallowed wildcards under the
> sample spec. See the second bullet point under "Semantics and
> Compilation". However, I wasn't convinced that that was a good idea
> either, which is why I put it under Additional Features (at the end).
> The described technique under that header would make this example work
> (probably -- I'd have to double-check the JLS).
>> I don't think supporting casts adds value to the feature. You can
>> already assign, for example, from ArrayList to List<String> without a
> That was where Josh was leaning when I asked him about it, too. The
> reason I thought it made sense was just for consistency's sake;
> basically, it is the only one of the five conversion contexts where
> this technique might work, but it doesn't. For assignments and method
> parameters, it will work, and for String and numeric conversions, it
> doesn't make any sense. Casting was the only one left.
>> If you want to hear about the approach that Joe is working on, I'll be
>> happy to describe it in person at your convenience (with Joe, if he
> I would definitely like to hear about it! How close is Joe to
> finishing a draft?
Joe hasn't started a draft!
Neal and I discussed some implementation strategies that could also
guide a specification. I'll send out more in the next few days.
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