[petsc-dev] declaring argument as const basic type in PETSc

[Barry Smith]

  You are absolutely correct in that it is violation of encapsulation that does not harm, it just irks me that such a great language can have a silly flaw.

   Barry

On Aug 17, 2011, at 6:27 PM, Chetan Jhurani wrote:

>> From: Barry Smith
>> 
>> On Aug 17, 2011, at 2:50 PM, Chetan Jhurani wrote:
>> 
>>> I never meant to say that one must put const ints in the
>>> declaration.
>> 
>>   Our problem is that because one compiler warns if the const is not listed in both prototype and
>> definition we must put it in both (to avoid tons of warning messages that people installing PETSc
>> should not see) we MUST put them in the declaration. Which we wanted to avoid since it is anti-
>> encapsulation.  So for now, they are forbidden in all PETSc code even though yes they can be useful in
>> implementations.
> 
> I understand.  One has to take care of many platforms and compilers
> that all behave differently.
> 
> Anyway, after this discussion I could realize why I have no problem with
> code that has const ints in declaration and definition and why it doesn't
> break encapsulation (for me).
> 
> The philosophy is that -- and I'm not telling this to convert anyone to
> my philosophy or to use my definition of encapsulation :-) -- just exposing
> inner details is not an encapsulation problem.  Rather, if the exposure
> allows the interface user to rely on it and suffer compatibility problems
> if the inner details change, only then is it an encapsulation problem (for
> me).
> 
> In the ongoing example, the user sees const int and can assume that
> function will not change the int.  If this behavior changes, say
> using a const_cast, or not having the const int in function definition,
> then it cannot affect the caller.  Inner details are exposed, but
> the caller cannot use the extra details to have any choice in a
> decision!  So nothing will break due to this exposure and no new
> dependency is created due to it.
> 
> "There is only one thing a philosopher can be relied upon to do,
> and that is to contradict other philosophers." -- William James
> 
> ;)
> 
> Chetan
> 
>