Valarray

[Marc Lepage]

Gabriel Dos Reis wrote:
> 
> Current CVS trees (both GCC and libstdc++-v3) are more up-to-date.

Thanks. I'm using GCC 2.95.x and awaiting stable releases, as I am working on
production code. However, I am on this list to track development, so I know when
to begin planning for upgrade to standard C++ (e.g. string streams).  :-)


> | Why doesn't valarray use more macro shenanigans (like _DEFINE_BINARY_OPERATOR(+,
> | plus)) to declare the operators within the class? See bits/std_valarray.h:140
> | for details.
> 
> Why should them be declared within then class? Where do you draw that
> requirement from?

I don't know about requirements. My observation is that instead of declaring:

      valarray<_Tp>& operator+= (const _Tp&);
      valarray<_Tp>& operator-= (const _Tp&);
      ...
      valarray<_Tp>& operator+= (const valarray<_Tp>&);
      valarray<_Tp>& operator-= (const valarray<_Tp>&);
      ...

you could automate the declarations using macros, in this fashion:

      #define _DECLARE_VALARRAY_AUGMENTED_ASSIGNMENT(_Op)\
          valarray<_Tp>& operator##_Op##= (const _Tp&);\
          valarray<_Tp>& operator##_Op##= (const valarray<_Tp>&);

      _DECLARE_VALARRAY_AUGMENTED_ASSIGNMENT(+)
      _DECLARE_VALARRAY_AUGMENTED_ASSIGNMENT(-)
      ...

This style of macro use is already employed later to actually define the
operators:

      _DEFINE_VALARRAY_AUGMENTED_ASSIGNMENT(+, plus)
      _DEFINE_VALARRAY_AUGMENTED_ASSIGNMENT(-, minus)

so I wondered why it wasn't used to declare them as well.


> | Similarly, why aren't the function objects defined using macros in the same
> | fashion? See bits/stl_function.h:49 for details.
> 
> Please, can you exapnd on this?

The function objects are declared as follows:

    template <class _Tp>
    struct plus : public binary_function<_Tp,_Tp,_Tp> {
      _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x + __y; }
    };

    template <class _Tp>
    struct minus : public binary_function<_Tp,_Tp,_Tp> {
      _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x - __y; }
    };

I wondered why macros weren't employed as in valarray, like this:

    #define _DEFINE_FUNCTIONAL_ARITHMETIC_OPERATION(_Op, _Name)\
    template <class _Tp>\
    struct _Name : public binary_function<_Tp,_Tp,_Tp> {\
      _Tp operator()(const _Tp& __x, const _Tp& __y) const { return __x _Op __y;
}\
    };

    _DEFINE_FUNCTIONAL_ARITHMETIC_OPERATION(+, plus)
    _DEFINE_FUNCTIONAL_ARITHMETIC_OPERATION(-, minus)


> | P.S. Not related to libstdc++-v3, has anyone had any experience wrapping
> | functors/valarray in more OO fashion, for dynamic binding and persistence? I've
> | been playing with that recently, and wouldn't mind comparing notes.
> 
> What do call "more OO fashion" ?

I mean:

    class AdaptableUnaryFunction :
        public std::unary_function<std::valarray<double>, std::valarray<double>
>
    {
    public:
        virtual ~AdaptableUnaryFunction() = 0;
        virtual result_type operator ()(const argument_type& arg) const = 0;
    };

-- 
Marc Lepage
Software Developer
Molecular Mining Corporation
http://www.molecularmining.com/