Re: mapper functions for 3.1

[John W. Eaton]

On 16-Feb-2008, David Bateman wrote:

| I see one issue with the charNDArray class. There the typedef for all
| the mapper functions are the same (i.e. int (*) (int)) but the return
| type of the mapper method itself might be different (cf isalpha to
| tolower). This is likely to cause issue with your scheme, and is in fact
| why the charNDArray mapper methods have different maps (dmap, smap,
| bmap) in my patch.. I'm not sure how to deal with that in your scheme,
| other than keeping the map names different. So you'll end up with 6
| different mapper methods in the Array<T> class at least.

I think this can be handled by using something like the following.

Add

  template <typename CT, typename RT, typename PT>
  class functor_with_conversion
  {
  private:
    typedef typename fcn_ptr<RT, PT>::TYPE fcn_ptr_type;
    fcn_ptr_type fptr;

  public:

    functor_with_conversion (fcn_ptr_type p) : fptr (p) { }

    CT operator () (PT arg) { return CT (fptr (arg)); }
  };

  template <typename CT, typename RT, typename PT>
  functor_with_conversion<CT, RT, PT>
  func_ptr_with_conversion (RT (*f) (PT))
  {
    return functor_with_conversion<CT, RT, PT> (f);
  }

to Array.h (or some other header specifically for these functor
classes) and then keep the declarations

  typedef int (*mapper) (int);
  boolNDArray bmap (mapper fcn) const;
  NDArray dmap (mapper fcn) const;
  charNDArray smap (mapper fcn) const;

in chNDArray.h and use

  boolNDArray
  charNDArray::bmap (mapper fcn) const
  {
    return MArrayN<char>::map<bool> (func_ptr_with_conversion<bool> (fcn));
  }

  NDArray
  charNDArray::dmap (mapper fcn) const
  {
    return MArrayN<char>::map<double> (func_ptr (fcn));
  }

  charNDArray
  charNDArray::smap (mapper fcn) const
  {
    return MArrayN<char>::map<char> (func_ptr_with_conversion<char> (fcn));
  }

in chNDArray.cc.  There might be a slick way to combine the functor
and functor_with_conversion classes using default template parameters
but I don't see it at the moment.

jwe