> High five, Karl. High five! :-)
> On Sep 30, 2012 6:46 AM, "Karl Rupp" <rupp at mcs.anl.gov > <mailto:rupp at mcs.anl.gov>> wrote: > > Hi, > > >>> ^^^ Note that this const is superfluous. > > Why is it superfluous? Isn't the second argument type const > char* const this way? > > It's superfluous for the same reason we don't "set" by > passing "const PetscInt". The const is irrelevant to the > caller. All it means is that the implementation doesn't > change the *its* copy (pass by value) and even that isn't > type checked with respect to the public declaration. It's > just clutter and suggests that the person who wrote it > doesn't understand types. > > > Which clearly I don't :-( > > So do we just go with typedef const char* VecType and > then all signatures are VecType? > > > yes, Jed is absolutely right on that. The important thing to keep in > mind here is that typedef is atomic, i.e. it is not a 'string > replacement' as opposed to what the C preprocessor does. > > Example: > #define VecType char* > int Set(const VecType) > expands to > int Set(const char*) > > However, with > typedef const char* VecType > int Set(const VecType) > there is no immediate string replacement, i.e. it is NOT the same as > int Set(const const char*) > with the compiler ignoring one of the const keywords. Instead, > denoting the precedence using brackets, the type passed to the Set() is > const {const char*} > which is a const copy to a const char*. Now, as 'const char*' is > copied when passed to the function anyways, the first 'const' is > superfluous as Jed pointed out. As a consequence, we can simply use > Set(VecType); > Get(VecType*); > which is pretty much the standard prototype for any pair of > Getter/Setter and also the way arguments of type PetscInt are handled. > > In conclusion, we have not only eliminated the preprocessor magic, > we are also able to provide a cleaned-up interface for XYZSetType() > and XYZGetType(). Thanks, Barry, for making the decision in favor of > a typedef :-) > > Best regards, > Karli > >
