On Sep 28, 2012, at 3:01 PM, Matthew Knepley <knepley at gmail.com> wrote:
> On Fri, Sep 28, 2012 at 3:17 PM, Karl Rupp <rupp at mcs.anl.gov> wrote:
> Hi,
>
>
> > The reason we use a #define instead of typedef is because of
> (...)
>
>
> We really want to be able to const the beast in many places and I couldn't
> get it to work with typedefs in a way natural for users. If you can come up
> with a clean natural way to handle the const we can switch.
>
> Ok, I see. Let me be a bit persistent then and hunt for occurrences of
> 'VecType' without 'const':
>
> $> grep -r "VecType" *.h | grep -v "const VecType"
> petscvec.h:.seealso: VecCreate(), VecType, VecSetType()
> petscvec.h: VecType - String with the name of a PETSc vector or the
> creation function
> petscvec.h:#define VecType char*
>
>
> Alright, so
> typedef const char * VecType;
> should work here. Let's check for MatType:
>
> Unfortunately no, this does not work, or we would have done this.
The problem is we/people may want to "build" XXXType values on the fly with
string operations like strcpy, strcat etc. You cannot do that into a const
char*, thus we/people would have to declare the place they build things as
char* instead of XXXType and that is "unnatural". Keep digging; we all agree
with you that it would be good to get rid of the #define.
I view this problem as a slight "flaw" in typedef, but perhaps C typedef
has a solution?
Barry
>
> Matt
>
> $>grep -r "MatType" *.h | grep -v "const MatType"
> petscmat.h:.seealso: MatCreate(), MatType, MatSetType()
> petscmat.h: MatType - String with the name of a PETSc matrix or the
> creation function
> petscmat.h:#define MatType char*
> petscmat.h:.seealso: MatGetFactor(), Mat, MatSetType(), MatType
> petscmat.h: Notes: MATMFFD is a specific MatType which uses the MatMFFD
> data structure
>
>
> So
> typedef const char * MatType;
> should also be fine here as well. Repeating the game for all PETSc-types with
> the following bash-beast (i.e. repeat the procedure above for every #define
> XYZType char*):
> for t in `grep -hr "Type char" *.h | sed '/^#define */!d; s///;' | sed '/
> char\*/!d; s///;'` ; do grep -r "${t}" *.h | grep -v "const ${t}"; done
>
> one finds only a single function which is not using a 'const' in front of any
> *Type defined via the preprocessor:
> PETSC_EXTERN PetscErrorCode MatColoringRegister(const char[],const
> char[],const char[],PetscErrorCode(*)(Mat,MatColoringType,ISColoring *));
> Now, assuming that 'const' was simply forgotten here, what about typedef-ing
> everything to 'const char *' then? It shouldn't be too much of a painful
> day...
>
>
>
> 2) Having Vec but PetscVecType would be terribly inconsistent mess.
> Better to switch everything in one painful day.
>
> In the context of what Matt said initially (of which I wasn't aware and I
> wouldn't have expected a general PETSc-type to be defined via a preprocessor
> define), it is indeed inconsistent.
>
> Best regards,
> Karli
>
>
>
>
> --
> What most experimenters take for granted before they begin their experiments
> is infinitely more interesting than any results to which their experiments
> lead.
> -- Norbert Wiener
