[saga-rg] deep copy / shallow copy

[Andre Merzky]

Hi all, 

during a discussion with Hartmut today, we stumbled over the
question of copy behavious for the SAGA objects.  Consider
following code:

----------------------------------------------------------------------
   0 saga::job_description jd_1;
   1
   2 jd_1.set_attribute ("SAGA_Host", "host_1");
   3
   4 cout << jd_1.get_attribute ("SAGA_Host")) << endl;
   5
   6
   7 saga::job_description jd_2 = jd_1;
   8
   9 cout << jd_2.get_attribute ("SAGA_Host")) << endl;
  10
  11 jd_2.set_attribute ("SAGA_Host", "host_2");
  12 
  13 cout << jd_1.get_attribute ("SAGA_Hoset")) << endl;
  13 cout << jd_2.get_attribute ("SAGA_Hoset")) << endl;
----------------------------------------------------------------------

What would that print?  If the copy in line 4 is a deep
copy, it would print:

  host_1                // jd_1 orig
  host_1                // jd_2 as copy from jd_1
  host_1                // jd_1 orig still
  host_2                // jd_2 newly set

if it is a shallow copy, it would be:

  host_1                // jd_1 orig
  <not defined>         // jd_2 not defined yet
  host_1                // jd_1 orig still
  host_2                // jd_2 newly set
  
if SAGA objects are only handled as references, it would be:

  host_1                // jd_1 orig
  host_1                // jd_2 as reference to jd_1
  host_2                // jd_1 newly set (via jd_1 ref)
  host_2                // jd_2 just the same as jd_1


As the SAGA implementation should obviously show the same
behaviour (either one for now), the spec needs to define
that obviously.

We think, that a default shallow copy is the most useful
one.  If for some objects a deep copy makes sense, a clone()
method could be defined, which has the explicit semantics of
a deep copy.  If a reference is needed for some object, the
native language can usually be used to obtain such one.

So, if shallow copy as default, all three of the above cases
seem easily implementable if needed.


If there are no opinions against that, I'll add the
respective note to the spec.

Many thanks, 

  Andre.
  
  

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