(j3.2006) How to assign to the declared-type part of a polymorphic allocatable array?

[Van Snyder]

Here's a nearly-as-ugly solution:

type :: H_t_0
  type(lon_t) :: Lon
  type(lat_t) :: Lat
end type H_t_0

type, extends(h_t_0) :: H_t
end type H_t

geo%h_t_0 = z%ZOT_to_geo()

Ugh.

On Thu, 2016-09-22 at 13:46 -0700, Van Snyder wrote:
> Here's an ugly solution, that gets uglier and uglier as more extensions
> of a type are created:
> 
> On Wed, 2016-09-21 at 19:57 -0700, Van Snyder wrote:
> > Is there a way to assign to the declared-type part of a polymorphic
> > allocatable array, other than one component at a time?
> > 
> > I have a type H_t (for horizontal geolocation) that contains latitude
> > and longitude.  It's agnostic whether the latitude is geocentric or
> > geodetic.  It has extensions H_Geoc (for geocentric latitude) and H_Geod
> > (for geodetic latitude), H_V_t (including a height component V, agnostic
> > whether geocentric or geodetic), H_V_Geoc (geocentric latitude and
> > height), H_V_Geod (geodetic latitude and height), and others.
> > 
> > I have an object
> > 
> >   class(h_t), allocatable :: Geo(:)
> > 
> > which I allocate
> > 
> >   if ( geodetic ) then
> >     allocate ( h_v_geod :: geo(n) )
> >   else
> >     allocate ( h_v_geoc :: geo(n) )
> >   end if
> 
> select type ( geo )
> class is ( h_geoc ) ! h_v_geoc is an extension of h_geoc
>   geo%h_t = z%ZOT_to_geo()
> class is ( h_geod ) ! h_v_geod is an extension of h_geod
>   geo%h_t = z%ZOT_to_geo()
> end select
> 
> I can't use a class default block because therein the declared type of
> geo would be h_t, and it wouldn't have a nonpolymorphic h_t component to
> which I can assign.
> 
> > I then want to fill the horizontal geolocations by applying an elemental
> > type-bound function to an array of a type ZOT_t, from which latitudes
> > and longitudes are computed.  The type ZOT_t represents a uniform
> > triangular grid on a (-1:1 X -1:1) square, which is then projected by a
> > zenitial orthogonal transformation onto a sphere.  The grid is developed
> > to a specified refinement, without regard to whether latitudes computed
> > from it will be ultimately interpreted as geocentric or geodetic.
> > Therefore, the result of the type-bound function ZOT_to_Geo is
> > type(H_t), not class(H_t).  So after allocating Geo, I'd like to assign
> > to its horizontal geolocation components using
> > 
> >   geo%h_t = z%ZOT_to_geo()
> > 
> > (size(z) == n) but we've only provided for a parent component, not a
> > "self" component, so geo%h_t doesn't exist.  I can't use
> > 
> >   geo = z%ZOT_to_geo()
> > 
> > for two reasons.  First, geo is polymorphic.  Second, it has a "v"
> > component, that I'm not yet ready to fill.
> > 
> > Is there something simpler than this:
> > 
> >   block
> >     type(h_t) :: T
> >     integer :: I
> >     do i = 1, n
> >       t = z(i)%ZOT_to_geo()
> >       geo(i)%lat = t%lat
> >       geo(i)%lon = g%lon
> >     end do
> >   end block
> > 
> > Ignoring for a while the "v" component of h_v_geod, I tried
> > 
> >   allocate ( geo, source=h_geod(h_t=z%zot_to_geo()) )
> > 
> > but that doesn't work because structure constructors aren't elemental
> > (how could they be?).  Maybe I could overload h_geod with an elemental
> > function; I haven't tried that yet.
> > 
> > I tried
> > 
> >   allocate ( h_geod :: geo, source = z%zot_to_geo() )
> > 
> > but that doesn't work because it has both a type spec and a source.
> > 
> > I did finally make this work, but it seems like a needlessly wordy
> > kludge:
> > 
> >   allocate ( geo, source = [ ( h_v_geod(h_t=z(i)%zot_to_geo(),v=0), i = 1, n ) ] )
> > 
> > Isn't there something simpler?
> > 
> > [BTW, it doesn't work with ifort 15.0.2.164.  It complains about a
> > missing field [LAT] not being initialized.  Maybe it's been repaired
> > already.  I have not yet been able to convince our SA to install the
> > latest Intel release.]
> > 
> > 
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