fieldPostBlit - what is wrong with this and workarounds

[Daniel Davidson]

On Thursday, 31 October 2013 at 15:56:45 UTC, Maxim Fomin wrote:
> On Thursday, 31 October 2013 at 14:03:28 UTC, Daniel Davidson 
> wrote:
>> Given this code:
>>
>>  import plus.tvm.rate_curve;
>>  struct T {
>>    RateCurve m;
>>  }
>>  struct S {
>>    const(T) rc;
>>  }
>>
>> I get this error: Error: mutable method 
>> plus.models.dossier.__unittestL42_1.T.__fieldPostBlit is not 
>> callable using a const object
>>
>> Is this fundamentally incorrect? I abandoned immutable in 
>> hopes that const would be more manageable and so far it has. 
>> But these types of issues still crop up and stop me in my 
>> tracks.
>>
>> What are the requirements on RateCurve and T for this to work?
>>
>> Thanks
>> Dan
>
> D language is fundamentally incorrect here. There are 
> sufficient issues in bugzilla (one which bearophile provided is 
> actually relevant, it shows same problem from a little bit 
> different aspect) and the problem tends to pop up quire 
> regularly. It looks like nothing is done because it is design 
> issue and although there were attempts to come up with, no idea 
> is viewed as final solution. The easiest way to solve problem 
> is to strip const.

I'm think you may be correct... but what specifically is 
incorrect about the language?
When I see __fieldPostBlit I get the feeling it is more an 
implementation issue than the language.

If as you suggest, D language is fundamentally broken - is it 
possible we can just get a plan for fixing it? To me this seems 
like a huge design hole and I come back to the threads with 
questions again and again and I really don't know how others 
manage the use of const/immutable.

I've already given up on immutable. If I have to strip const as 
well then that is a huge pain and unfortunate since the concept 
seems sound and well argued in TDPL. Trying to mess with 
mutable/const/immutable on mostly working code is like playing 
whack a mole.