Javari's Reference Immutability

[Regan Heath]

But java has immutable strings, right?
http://www.janeg.ca/scjp/pkglang/immutable.html

That in itself is a form of 'const' covering the most common use cases.

Regan

On Tue, 25 Jul 2006 18:21:58 -0600, Hasan Aljudy <hasan.aljudy at gmail.com>  
wrote:
> I think the question is: what's the point?
> Clearly, Java's lack of const didn't prevent it from the having some of  
> the best libraries there are.
>
> Reiner Pope wrote:
>> I've read the paper on Javari's reference immutability (thanks to  
>> Bruno) and it has an interesting idea: a synthesis of dynamic and  
>> static checking.  This makes it easier to interface const-aware code  
>> with const-unaware code. It can be demonstrated as follows:
>>  Date a = new Date(); // a mutable date
>> readonly Date b = a; // A readonly view of a
>> Date c = (mutable) b; // The compiler bypass static checking, but  
>> inserts dynamic checks.
>> a.modify(); // OK
>> b.modify(); // Compile-time error
>> c.modify(); // Runtime error
>>   How could you implement the runtime checking? A first thought would  
>> be to add the following assert to the in contract of every mutating  
>> method:
>>    assert(!isConst);
>>  But that requires that the /class/ knows the const-ness of the  
>> reference it is accessed through, which I don't think it does.
>>  The other alternative seems to be a much easier one: simply modify the  
>> vtbl so that all mutating functions point to a single line:
>>    assert(false, "Trying to modify a class through a readonly view");
>>  The problem with that is that I suspect the vtable is stored with the  
>> class, not the reference, so modifying the vtable will modify it for  
>> all other references, even if they aren't readonly.
>>  Clearly, Javari manages such checking, and it claims to manage it in a  
>> Java-compatible (backwards-compatible) way. How is it done in Javari,  
>> and how could it be done in D?
>>   Cheers,
>>  Reiner