more band aid coming - Object methods on 'any' tvars

Maurizio Cimadamore maurizio.cimadamore at oracle.com
Mon Jan 19 13:50:16 UTC 2015


Hi Duncan
thanks for the example - the field access at offset 1 is the one for
'isPresent' which is a boolean (regardless of how the class is
specialized) - why should there be an annotation on it?

Maurizio

On 19/01/15 13:45, MacGregor, Duncan (GE Energy Management) wrote:
> Here’s my little optional class and the output from javap. As you can see
> there is no annotation for the getField at offset 1 in public T get(), but
> there is for the getField() in public boolean isPresent().
>
> Duncan.
>
> On 19/01/2015 11:26, "Maurizio Cimadamore"
> <maurizio.cimadamore at oracle.com> wrote:
>
>> Hi Duncan,
>> I've come back to this, and don't seem to be able to reproduce the
>> problem; can you please post a bigger snippet that reproduces the issue?
>>
>> Thanks
>> Maurizio
>>
>> On 16/01/15 15:22, MacGregor, Duncan (GE Energy Management) wrote:
>>> Thanks for that, I can now write a sensible optional class and it
>>> behaves
>>> as expected.
>>>
>>> One bug I have found is that getField is not always being correctly
>>> specialised in all cases. Specifically a final boolean field used in an
>>> if
>>> statement such as
>>>
>>> if (!isPresent) { throw... } else { return otherField; }
>>>
>>> Was not marked for specialisation and caused a byte code verification
>>> error, but using a method to get the field value worked perfectly.
>>>
>>> Duncan.
>>>
>>> On 16/01/2015 12:29, "Maurizio Cimadamore"
>>> <maurizio.cimadamore at oracle.com> wrote:
>>>
>>>> I've just pushed a compiler/specializer patch that adds support for
>>>> T.default.
>>>>
>>>> This is internally handled as an 'aconst_null' which has a
>>>> BytecodeMapping entry attached to it (in case T is an 'any' type-var).
>>>> The specializer will then replace the aconst_null with the proper
>>>> XYZconst_0.
>>>>
>>>> Again, to keep things simpler at this stage, stuff like 'int.default'
>>>> will not work (parser will reject that). This should still be enough to
>>>> get you going with the experiments.
>>>>
>>>> Happy coding!
>>>>
>>>> Maurizio
>>>>
>>>>
>>>> On 15/01/15 11:35, Maurizio Cimadamore wrote:
>>>>>> That is how I was intending to implement it, but if I don¹t want to
>>>>>> subclass then I need have a type something like
>>>>>>
>>>>>> Class Optional<any T> {
>>>>>> 	final T value;
>>>>>> 	final boolean hasValue;
>>>>>> }
>>>>>>
>>>>>> And that means I need to set value to something, even for the empty
>>>>>> case.
>>>>>> Hence the need for defaults.
>>>>> Right - I hear you.
>>>>>
>>>>> Maurizio
>>>>>> Duncan.
>>>>>>



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