[GiNaC-devel] Why does this program crash?

[Vladimir V. Kisil]

	Dear All,

	I investigated the crash. It is caused by an infinite loop of calls

in GiNaC::ex::ex at /usr/include/ginac/ex.h:265
in GiNaC::symbol::eval at /usr/include/ginac/symbol.h:49
in GiNaC::ex::construct_from_basic(GiNaC::basic const&) from /usr/lib/libginac.so.5

  This happens because the assignment

  symbol x("x");
  x = realsymbol("y");

  is done through the inherited operator
  const basic & basic::operator=()

  which resets the status_flags::evaluated (for different classes) and
  this flag is never set again for symbols.

  Now the first question is: do we really want a symbol to be assigned
  through operator=? If the answer is "yes" then there is the second
  question is: to repair the situation either
  * an adjusted symbol::operator=() shall be provided, which sets the
  flag evaluated; or
  * at ex:eval() we shall set status_flags::evaluated for GiNaC::symbol and its
  children?

  Another option is: basic::operator= shall reset status_flags::evaluated
  only if another object is not of a child class.

  My understanding of GiNaC is not sufficient to take decision on this
  matter.  

  Best wishes,
  Vladimir
-- 
Vladimir V. Kisil                 http://www.maths.leeds.ac.uk/~kisilv/
  Book:     Geometry of Mobius Transformations     http://goo.gl/EaG2Vu
  Software: Geometry of cycles          http://moebinv.sourceforge.net/
>>>>> On Sat, 14 May 2016 10:03:26 +0100, "Vladimir V. Kisil" <kisilv at maths.leeds.ac.uk> said:

    VVK> 	Dear Jan,

    VVK> 	Please accept my apology, you did send a complete
    VVK> example and I have overseen that. In my opinion, the issue is
    VVK> not with the inheritance as such. Symbol x is not assumed to be
    VVK> a left value. There are GiNaC::ex for this.

    VVK>   Best wishes, Vladimir -- Vladimir V. Kisil
    VVK> http://www.maths.leeds.ac.uk/~kisilv/ Book: Geometry of Mobius
    VVK> Transformations http://goo.gl/EaG2Vu Software: Geometry of
    VVK> cycles http://moebinv.sourceforge.net/
>>>>> On Sat, 14 May 2016 09:21:23 +0100, "Vladimir V. Kisil"
    VVK> <kisilv at maths.leeds.ac.uk> said:

>>>>> On Sat, 14 May 2016 04:53:54 +0200, Jan Rheinländer <jrheinlaender at gmx.de> said:

    JR> Dear Vladimir, realsymbol is not my derived class. See
    JR> ginac/symbol.h !

    VVK> Yes, and as far as I am aware there is no problem with
    VVK> realsymbol in GiNaC. Furthermore, in my own project (see the
    VVK> end of the email) I have successfully derived several new
    VVK> classes following the advise from the GiNaC tutorial.

    VVK> If you are looking for an assistance you need to provide a
    VVK> complete piece of software, including the full description of
    VVK> your derived class, which causes the issue.

    VVK> Best wishes, Vladimir -- Vladimir V. Kisil
    VVK> http://www.maths.leeds.ac.uk/~kisilv/ Book: Geometry of Mobius
    VVK> Transformations http://goo.gl/EaG2Vu Software: Geometry of
    VVK> cycles http://moebinv.sourceforge.net/
    VVK> _______________________________________________ GiNaC-devel
    VVK> mailing list GiNaC-devel at ginac.de
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