[Octave-bug-tracker] [bug #49421] Can't set properties in a subclass after chaining constructors in base class

[Mike Miller]

Update of bug #49421 (project octave):

                Category:                    None => Interpreter            
              Item Group:                    None => Matlab Compatibility   
                  Status:                    None => Need Info              
        Operating System:               GNU/Linux => Any                    
                 Summary: Can't set properties in a subclass => Can't set
properties in a subclass after chaining constructors in base class

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Follow-up Comment #1:

I am able to reproduce this error with the following minimal example:


$ cat @base/base.m 
classdef base < handle
  properties
    x;
    y;
  endproperties
  methods
    function self = base (a, b)
      if (nargin == 0)
        self.x = 0;
        self.y = pi;

      else
        self = base ();
        self.x = a;
        self.y = b;

      endif
    endfunction
  endmethods
endclassdef


$ cat @derived/derived.m 
classdef derived < base
  properties
    z;
  endproperties
  methods
    function self = derived (a = 0, b = pi, c = 42)
      address@hidden (a, b);
      self = builtin ("subsasgn", self, substruct (".", "z"), c);
    endfunction
  endmethods
endclassdef




The key part of this minimal example is that the base constructor overwrites
the "self" object with a new instance of type base, when it really should be a
derived object. Thus the derived constructor gets back a base object instead
of the one it originally started with, and it doesn't have the expected
properties.

What does Matlab do? Is there a correct way to do constructor chaining if this
is not the right way to do it? Instead of doing something like "self = base
()" should that be "address@hidden ()" instead? Should both work?

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  <http://savannah.gnu.org/bugs/?49421>

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