Function types versus arrays

[Alex Buckley]

Neal raises a fair point. I recognize that arrays of function types are 
as potentially unsafe at runtime as arrays of non-wildcard parameterized 
types.

And this is the same problem one sees when passing variables of 
parameterized types as varargs parameters. The varargs method body can 
silently do unsafe things, thanks to Object being a universal supertype.

Banning arrays of function types is an option. It somewhat conflicts 
with Project Coin's promotion of [] syntax to read/write collections.

I am interested in people's thoughts on the limitations of arrays of 
parameterized types. (Reification was not and is not an option, so 
please no ranting about the stupid implications of erasure.) Does anyone 
care about arrays anymore?

Alex

Rémi Forax wrote:
> Le 07/02/2010 19:41, Neal Gafter a écrit :
>> I've been asked if arrays and function types will play nicely
>> together.  Specifically, for example, whether or not something like
>> the following will be allowed:
>>
>> #String(String)[] arrayOfFunction = new #String(String)[10];
>>
>> The current draft spec, by the absence of any constraining rules,
>> implies yes.  But if I have to guess, I would say the end result of
>> project lambda will probably say no.  Although we haven't talked much
>> about implementation techniques, I'm not aware of any proposed
>> implementation technique that would allow this without opening a hole
>> in the type system.
>>
>> I don't know whether we should consider this important or not (I
>> don't; I'm perfectly happy using java.util.List), but if it is
>> important then someone should be thinking about what needs to happen
>> (VM support?) to make it work.
>>    
> 
> For the record the problem is:
> 
> #String(String)[] arrayOfFunction = new #String(String)[10];
> Object[] array = arrayOfFunction;
> array[0] = #int() (2);
> 
> The last line should raise an array store exception.
> So the VM should be aware of the precise type of the array of function.
> 
> Currently, neither the anonymous class translation nor the method handle one
> provide reified function type so array of function types are unsafe.
> 
> Because function type doesn't exist in the language, I propose to make 
> the syntax
> for an array of function type (#String(String)[]) illegal.
> 
> I'm also happy with List, perhaps we should introduce a new interface 
> ReadOnlyList
> which is a super type of List and array of objects but that another story.
> 
>> Cheers,
>> Neal
>>    
> 
> Rémi
>