ov-null-mat.cc

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//
// Copyright (C) 2008-2025 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// This file is part of Octave.
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////////////////////////////////////////////////////////////////////////
 
#if defined (HAVE_CONFIG_H)
#  include "config.h"
#endif
 
#include "ov-null-mat.h"
#include "ops.h"
#include "defun.h"
 
DEFINE_OV_TYPEID_FUNCTIONS_AND_DATA (octave_null_matrix, "null_matrix",
                                     "double");
 
const octave_value octave_null_matrix::instance (new octave_null_matrix ());
 
static octave_base_value *
default_null_matrix_numeric_conversion_function (const octave_base_value& a)
{
  // The cast is not necessary?
  // const octave_null_matrix& v = dynamic_cast<const octave_null_matrix&> (a);
 
  return a.empty_clone ();
}
 
octave_base_value::type_conv_info
octave_null_matrix::numeric_conversion_function () const
{
  return octave_base_value::type_conv_info
         (default_null_matrix_numeric_conversion_function,
          octave_matrix::static_type_id ());
}
 
DEFINE_OV_TYPEID_FUNCTIONS_AND_DATA (octave_null_str, "null_string", "char");
 
const octave_value octave_null_str::instance (new octave_null_str ());
 
static octave_base_value *
default_null_str_numeric_conversion_function (const octave_base_value& a)
{
  // The cast is not necessary?
  // const octave_null_str& v = dynamic_cast<const octave_null_str&> (a);
 
  return a.empty_clone ();
}
 
octave_base_value::type_conv_info
octave_null_str::numeric_conversion_function () const
{
  return octave_base_value::type_conv_info
         (default_null_str_numeric_conversion_function,
          octave_char_matrix_str::static_type_id ());
}
 
DEFINE_OV_TYPEID_FUNCTIONS_AND_DATA (octave_null_sq_str, "null_sq_string",
                                     "char");
 
const octave_value octave_null_sq_str::instance (new octave_null_sq_str ());
 
static octave_base_value *
default_null_sq_str_numeric_conversion_function (const octave_base_value& a)
{
  // The cast is not necessary?
  // const octave_null_sq_str& v = dynamic_cast<const octave_null_sq_str&> (a);
 
  return a.empty_clone ();
}
 
octave_base_value::type_conv_info
octave_null_sq_str::numeric_conversion_function () const
{
  return octave_base_value::type_conv_info
         (default_null_sq_str_numeric_conversion_function,
          octave_char_matrix_sq_str::static_type_id ());
}
 
OCTAVE_BEGIN_NAMESPACE(octave)
 
DEFUN (isnull, args, ,
       doc: /* -*- texinfo -*-
@deftypefn {} {@var{tf} =} isnull (@var{x})
Return true if @var{x} is a special null array, string, or single quoted
string.
 
Indexed assignment with such a null value on the right-hand side should delete
array elements.  This function is used in place of @code{isempty} when
overloading the indexed assignment method (@code{subsasgn}) for user-defined
classes.  @code{isnull} is used to distinguish between these two cases:
 
@code{@var{A}(@var{I}) = []}
 
and
 
@code{@var{X} = []; @var{A}(@var{I}) = @var{X}}
 
In the first assignment, the right-hand side is @code{[]} which is a special
null value.  As long as the index @var{I} is not empty, this code should
delete elements from @var{A} rather than perform assignment.
 
In the second assignment, the right-hand side is empty (because @var{X} is
@code{[]}), but it is @strong{not} null.  This code should assign the empty
value to elements in @var{A}.
 
An example from Octave's built-in char class demonstrates the interpreter
behavior when @code{isnull} is used correctly.
 
@example
@group
str = "Hello World";
nm = "Wally";
str(7:end) = nm                # indexed assignment
  @result{} str = Hello Wally
str(7:end) = ""                # indexed deletion
  @result{} str = Hello
@end group
@end example
@seealso{isempty, isindex}
@end deftypefn */)
{
  if (args.length () != 1)
    print_usage ();
 
  return ovl (args(0).isnull ());
}
 
/*
%!assert (isnull ([]), true)
%!assert (isnull ([1]), false)
%!assert (isnull (zeros (0,3)), false)
%!assert (isnull (""), true)
%!assert (isnull ("A"), false)
%!assert (isnull (''), true)
%!assert (isnull ('A'), false)
%!test
%! x = [];
%! assert (isnull (x), false);
*/
 
OCTAVE_END_NAMESPACE(octave)