[GiNaC-devel] [BUG] clifford::op() versus tensor::replace_contr_index

[Sheplyakov Alexei]

Dear all,

I've tried making ex_to<T> functions [more] type-safe, like this:

diff --git a/ginac/ex.h b/ginac/ex.h
index 3070b7a..79f872b 100644
--- a/ginac/ex.h
+++ b/ginac/ex.h
@@ -949,7 +949,8 @@ inline bool is_exactly_a(const ex &obj)
 template <class T>
 inline const T &ex_to(const ex &e)
 {
-	GINAC_ASSERT(is_a<T>(e));
+	if (__builtin_expect(! is_a<T>(e), 0))
+		throw std::bad_cast();
 	return static_cast<const T &>(*e.bp);
 }

and got failure in exam_clifford (to be more specific, last expression
in clifford_check4 triggered bad_cast). I've found a simple[r] example
which fails in the same way:

#include <iostream>
#include <stdexcept>
#include "ginac.h"
using namespace GiNaC;

int main(int argc, char** argv)
{
	symbol d("D");
	varidx mu(symbol("mu"), d),
				 nu(symbol("nu"), d);
	ex e = lorentz_g(mu, nu)*dirac_gamma(nu.toggle_variance());
	e = e.simplify_indexed();
	return 0;
}

The reason of this error seems to be inconsistency between clifford::op
and tensor::replace_contr_index. tensor::replace_contr_index expects
any subexpression of `indexed' referenced via op() to be `idx' (see
tensor.cpp:398). On the other hand, `clifford' objects make their
representation label accessible via op(), so this assumption is incorrect.

So, the questions are:

1) Any ideas how to fix this?
2) In general, is it OK for class derived from indexed return something
   which is *not* idx (or derived from it) via op()?

Best regards,
 Alexei

-- 
All science is either physics or stamp collecting.

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