[Octave-bug-tracker] [bug #58105] isfield needs time proportional to number of fields

[anonymous]

Follow-up Comment #1, bug #58105 (project octave):

The "map_value" member of classes "octave_struct" and "octave_scalar_struct"
is very inefficient because it copies all the objects in the container. A fix
would be adding member  "isfield" in the classes "octave_value" ,
"octave_base_value" , "octave_struct" and "octave_scalar_struct" that
redirects call to "isfield" member in classes "octave_map" and
"octave_scalar_map" and changing "/libinterp/octave-value/ov-struct.cc
line:1920" 
from

      octave_map m = args(0).map_value ();

to

      const octave_value& m = args(0);


However extensive use of "map_value" in the internal API has the effect of
overall reduction in the performance. A more general fix would be adding
members "map_ref" and "scalar_map_ref" in "octave_value" and the related
classes


const map_ref& () const;

const scalar_map_ref& () const;


Users should be encouraged to use them instead of "map_value" if they need a
read only view to map object.

As a workaround you can define "isfield" as:


function c = isfield (a, b)
  try
    a.(b);
    c = 1;
  catch
    c = 0;
  end
endfunction


Or a more  complete workaround:

function c = isfield (a, b)
  if b.iscell ()
    c = ismember (b, fieldnames (a));
  else
    try
      a.(b);
      c = 1;
    catch
      c = 0;
    end
  end
end




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