[Proto] possible loss of expression wrappers in pass-through transforms

[Robert Valkenburg <rj.valkenburg@…>]

extended expressions seem to be getting unwrapped in proto pass through transforms.

Others have not observed this effect so it may be a compiler/platform issue (or programmer of course)

I've attached a smallish (~160 lines) file that only depends on "boost/proto/proto.hpp"

The results are as follows (gcc 4.4.1 linux FC 11, x86_64 platform)

g++ -Wall -I/home/users/robert/linux_x86_64/src/boost_1_42_0 test_boost_proto.cpp -o test_boost_proto

test_boost_proto.cpp: In function ‘void clifford::evaluate(Res&, const clifford::ga_expr<Expr>&) [with Res = clifford::multivector<clifford::cga3::rotator_basis, clifford::cga3::cga3>, Expr = boost::proto::exprns_::expr<clifford::tag::reverse_, boost::proto::argsns_::list1<clifford::ga_expr<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const clifford::multivector<clifford::cga3::ebivector_basis, clifford::cga3::cga3>&>, 0l> > >, 1l>]’:

test_boost_proto.cpp:126: instantiated from ‘clifford::multivector<B, A>& clifford::multivector<B, A>::operator=(const clifford::ga_expr<T>&) [with T = boost::proto::exprns_::expr<clifford::tag::reverse_, boost::proto::argsns_::list1<clifford::ga_expr<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const clifford::multivector<clifford::cga3::ebivector_basis, clifford::cga3::cga3>&>, 0l> > >, 1l>, B = clifford::cga3::rotator_basis, A = clifford::cga3::cga3]’

test_boost_proto.cpp:164: instantiated from here

test_boost_proto.cpp:103: error: no matching function for call to ‘evaluate_expr(clifford::multivector<clifford::cga3::rotator_basis, clifford::cga3::cga3>&, boost::proto::exprns_::expr<clifford::tag::reverse_, boost::proto::argsns_::list1<const clifford::ga_expr<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const clifford::multivector<clifford::cga3::ebivector_basis, clifford::cga3::cga3>&>, 0l> >&>, 1l>)’

The clifford::ga_expr<> got removed so it was unable to find evaluate_expr()

[Robert Valkenburg <rj.valkenburg@…>]

self contained program which shows expression unwrapping

[Eric Niebler]

(In [61782]) pass_through transform doesn't strip expression wrappers, fixes #4175