logical const without casts!

[Steven Schveighoffer]

On Thu, 29 Sep 2011 13:26:11 -0400, Steven Schveighoffer  
<schveiguy at yahoo.com> wrote:

> On Thu, 29 Sep 2011 13:06:55 -0400, Simen Kjaeraas  
> <simen.kjaras at gmail.com> wrote:
>
>> On Thu, 29 Sep 2011 16:54:24 +0200, Steven Schveighoffer  
>> <schveiguy at yahoo.com> wrote:
>>
>>> I just thought of an interesting way to make a logical const object  
>>> without casts.  It requires a little extra storage, but works without  
>>> changes to the current compiler (and requires no casts).
>> [snip]
>>> What do people think about this?
>>
>> This is what I think about it:
>>
>> class A {
>>      int n;
>>      void delegate( ) dg;
>> }
>>
>> pure
>> A createAnA( int n ) {
>>      A result = new A;
>>      result.n = n;
>>      result.dg = (){ result.n++; };
>>      return result;
>> }
>>
>> void main( ) {
>>      immutable A tmp = createAnA( 3 );
>>      assert( tmp.n == 3 );
>>      tmp.dg();
>>      assert( tmp.n == 3 );
>> }
>
> I agree this breaks immutability, and needs to be addressed.  I think  
> probably implicit casting of delegates (or items that containe  
> delegates) to immutable from strong-pure functions should be disallowed.
>
> But it's not the pattern I described, and uses a relatively new trick  
> (implicit immutable casting).  I'll file a bug for this case.
>

http://d.puremagic.com/issues/show_bug.cgi?id=6741

-Steve