[GiNaC-devel] remove_dirac_ONE() and documentation patches

[Vladimir V. Kisil]

	Dear All,

	I finally managed to check Alexey's proposition to wrap the
  throwing remove_dirac_ONE function. It indeed prevents my Windows app
  from crashing. Thus I attach the respective light-weighted patches.

  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 Thu, 23 May 2019 15:32:12 +0400, Alexey Sheplyakov <asheplyakov at YANDEX.ru> said:

    ASh> Hi,

    ASh> 23.05.2019, 10:44, "Vladimir V. Kisil"
    ASh> <kisilv at maths.leeds.ac.uk>:
    >>         Dear Alexey,
    >> 
    >>         I am attaching another iteration of the patch as
    >> suggested. The   exception-free method is used internally for a
    >> better protection.

    ASh> Firstly making two almost identical copies of remove_dirac_ONE
    ASh> is definitely a bad idea.  Two possible approaches are:

    ASh> a) wrap exception-throwing remove_dirac_ONE like this

    ASh> ex remove_dirac_ONE(const ex& e, bool& success, unsigned char
    ASh> rl, unsigned options) {          ex ret;          try {        
    ASh>         ret = remove_dirac_ONE(e, rl, options);          }
    ASh> catch (...) {                 success = false;                
    ASh> ret = _ex0;          }          return ret; }

    ASh> This way exceptions will propagate within ginac.dll itself
    ASh> only, and there's no code duplication.

    ASh> b) alternatively one could move the actual computation to
    ASh> non-throwing variant of remove_dirac_ONE, and make a wrapper
    ASh> which does throw exceptions:

    ASh> ex remove_dirac_ONE(const ex& e, unsigned char rl, unsigned
    ASh> options) {     bool success = true;     ex ret =
    ASh> remove_dirac_ONE(e, success, rl, options);     if (!success) {
    ASh>         // perhaps non-throwing variant should set an integer
    ASh> status instead of a bool flag, so a more specific exception can
    ASh> be thrown         throw std::runtime_error("some meaningful
    ASh> error message here");     }      return ret; }

    ASh> Secondly I don't quite get what's the point of replacing the
    ASh> throwing variant of remove_dirac_ONE, and throwing the very
    ASh> same exception manually:

    >> + bool success; + if (! ex_to<idx>(mu).is_dim_numeric())
    >> throw(std::invalid_argument("clifford_to_lst(): index should have
    >> a numeric dimension")); unsigned int D =
    >> ex_to<numeric>(ex_to<idx>(mu).get_dim()).to_int(); @@ -1341,7
    >> +1399,9 @@ lst clifford_to_lst(const ex & e, const ex & c, bool
    >> algebraic) || (! is_a<numeric>(pow(c.subs(mu == i,
    >> subs_options::no_pattern), 2)))) algebraic = false; lst V; - ex
    >> v0 =
    >> remove_dirac_ONE(canonicalize_clifford(e+clifford_prime(e)))/2; +
    >> ex v0 =
    >> remove_dirac_ONE(canonicalize_clifford(e+clifford_prime(e)),
    >> success)/2; + if (!success) +
    >> throw(std::invalid_argument("clifford_to_lst(): the argument is
    >> not a Clifford vector"));

    ASh> I.e. why can't we keep calling

    ASh> ex v0 =
    ASh> remove_dirac_ONE(canonicalize_clifford(e+clifford_prime(e)))/2;

    ASh> and have remove_dirac_ONE throw an appropriate exception?

    >> Previously remote_dirac_ONE() reported that an expression is not
    >> a Clifford scalar by throwing an exception.  This produced
    >> crashes in Qt applications on Windows.

    ASh> Not really. Throwing exceptions across shared libraries (DLLs)
    ASh> on Windows is a little bit tricky, but it's certainly possible.
    ASh> The crucial point is to make all DLLs use the same C++ runtime
    ASh> (which implies the C++ runtime should be linked dynamically
    ASh> into all DLLs linked into the application).

    ASh> Also patching just remove_dirac_ONE is sort of pointless, since
    ASh> most GiNaC methods and functions throw exceptions too.

    ASh> Best regards, Alexey

 
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