experiences with prototype

Peter Levart peter.levart at gmail.com
Tue Feb 3 21:05:14 UTC 2015


Hi Maurizio,

I see. I thought this could be a nice idiom for boxing, since the following:

(Object) 42

...is legal and results in an Integer object at runtime.

But I don't know if a checkcast is actually inserted for (Object). Could 
javac redundantly do it in case casting to Object is from expression of 
<any> type and also equip checkcast with BMA indicating the type of 
expression so that specialization could replace it with boxing code?

Regards, Peter


On 02/03/2015 08:09 PM, Maurizio Cimadamore wrote:
>
> On 03/02/15 18:46, Maurizio Cimadamore wrote:
>> I will also investigate on the crash you are getting... 
> Hi Peter,
> the crash is coming from this code in AbstractCollection (see code in 
> bold):
>
>     public boolean contains(Object o) {
>         __WhereVal(E) {
>             Iterator<E> it = iterator();
>             if (o == null) {
>                 return false;
>             } else {
>                 while (it.hasNext())
> *if (o.equals((Object) it.next()))*
>                         return true;
>             }
>             return false;
>         }
>         __WhereRef(E) {
>             Iterator<E> it = iterator();
>             if (o == null) {
>                 while (it.hasNext())
>                     if (it.next() == null)
>                         return true;
>             } else {
>                 while (it.hasNext())
>                     if (o.equals(it.next()))
>                         return true;
>             }
>             return false;
>         }
>     }
>
> I believe that, apart from the obvious javac bug, the code has an 
> issue, as it.next() is supposed to return a value there, but you are 
> casting to Object?
>
> For the records - a simpler test case for the bug is this:
>
> class Foo<any E> {
>     E e;
>     E get() { return e; }
>
>     void test() {
>         __WhereVal(E) {
>             Object o = (Object)get();
>         }
>     }
> }
>
> Maurizio



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