Lambda and JSR 292 method handle

[Howard Lovatt]

You could reify lambda's, see:

http://www.artima.com/weblogs/viewpost.jsp?thread=277879

for details. This would solve many of the erasure 'issues'. But as Neal's
example shows, not in all cases.

2009/12/23 Neal Gafter <neal at gafter.com>

> I don't think there is an option to reify function types.  That's because
> generics are already non-reified.  In this code
>
> *<T> #T() constant(T t) {
>     return #() t;
> }
> *
>
> the returned lambda cannot, in principle, be reified if generics are not
> reified.  This is independent of whether function types are mapped to
> interfaces, method handles, or something else.  There may be issues with it,
> but they aren't "disadvantages" except by comparison to a scheme that does
> not have these issues, and no such scheme has been proposed.
>
>
> On Wed, Dec 23, 2009 at 1:06 PM, Howard Lovatt <howard.lovatt at iee.org>wrote:
>
>> Presumably the problems with using generic style annotations and erasing
>> the
>> actual type include:
>>
>>   1. Can't have two methods of the same name only distinguished by lambda
>>
>>   type, e.g. filter( #boolean(int) ) and filter( #boolean(float) )
>>
>
> These are distinguished in CfJ, but not in a hypothetical erasure to
> MethodHandle.
>
>
>>   2. Can't have arrays of lambdas that are type safe, e.g. new #(int)()[ n
>>   ]; // Illegal
>>
>
> Right.
>
>
>>   3. Can't have instanceof tests (this might be possible since type
>>
>>   information is carried at runtime)
>>
>
> No, type information cannot, in principle, be guaranteed to be available at
> runtime unless generics are reified.
>
>
>>   4. Can't have primitive types (this might be fixable with an extension
>> to
>>   the signature attribute)
>>   5. Can't have static fields that are lambdas (this might be fixable with
>>
>>   an extension to the signature attribute)
>>
>
> Right: the signature attributes would be extended to express function
> types, addressing these two issues.
>
>
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-- 
 -- Howard.