Reified generics in Java

Neal Gafter post a blog entry
about adding reified generics to Java.
I likethat proposal mostly because
developpers will have the choice betweeen reified or not reified
generics.

About the syntax, i think it's better to use an anotation
than to re-use the keyword class. Annotating a type variable
is not currently allowed but it seems that the upcoming
JSR 308
will allow that.

 class ArrayList&lt;<strong>@Reified</strong> E&gt; {
   ...
 }

 class ArrayList&lt;<strong>class</strong> E&gt; {
   ...
 }

The big question is why tagging the type variable
and not the parametrized type.


I'm not sure that allowing to declare on a same parametrized type
refied type variable and non refied is a good idea,
because i don't see a use case.

 class HashMap<@Reified K,V> {

 }

Here, HashMap is not refiable because V
is not refiable. So what is the need of half reified type ?

Else, i not sure about the fact that allowing reified generics
requires to change collection interfaces.
Allowing reified interfaces will just allow safe cast/instanceof,
i wonder if it worth all problems linked to the introduction
of a new collection hierarchy.
It's perhaps up to a collection implementor to decide if a
collection implentation will use or not reified generics.

To end, i've recently read a paper of Mirko Viroli about
how to represent wildcard types at compiler level
but i'am not aware of any work about that at VM level.

Rémi