Hi, continuing to work through the user guide boost_1_38_0/doc/html/proto/users_guide.html, I reached the section Retaining POD-ness with BOOST_PROTO_EXTENDS() I fail to compile the following code with intel10: --------------------------CODE----------------------------- #include <iostream> #include <vector> #include <cmath> #include <boost/proto/core.hpp> #include <boost/proto/tags.hpp> #include <boost/proto/context.hpp> #include <boost/proto/domain.hpp> #include <boost/mpl/assert.hpp> using namespace boost; // Define a placeholder type template<int I> struct placeholder {}; // A type to be used as a domain tag (to be defined below) struct calculator_domain; struct calculator_context : proto::callable_context< calculator_context const > { // Values to replace the placeholders std::vector<double> args; // Define the result type of the calculator. // (This makes the calculator_context "callable".) typedef double result_type; // Handle the placeholders: template<int I> double operator()(proto::tag::terminal, placeholder<I>) const { return this->args[I]; } }; // The calculator<> expression wrapper makes expressions // function objects. template< typename Expr> struct calculator { // Use BOOST_PROTO_BASIC_EXTENDS() instead of proto::extends<> to // make this type a Proto expression extension: BOOST_PROTO_BASIC_EXTENDS(Expr, calculator<Expr>, calculator_domain) // Define operator[] to build expression templates: BOOST_PROTO_EXTENDS_SUBSCRIPT() // Define operator= to build expression templates: BOOST_PROTO_EXTENDS_ASSIGN() typedef double result_type; // Hide base_type::operator() by defining our own which // evaluates the calculator expression with a calculator context. result_type operator()( double d1 = 0.0, double d2 = 0.0 ) const { // As defined in the Hello Calculator section. calculator_context ctx; // ctx.args is a vector<double> that holds the values // with which we replace the placeholders (e.g., _1 and _2) // in the expression. ctx.args.push_back( d1 ); // _1 gets the value of d1 ctx.args.push_back( d2 ); // _2 gets the value of d2 return proto::eval(*this, ctx ); // evaluate the expression } }; // Define a calculator domain. Expression within // the calculator domain will be wrapped in the // calculator<> expression wrapper. struct calculator_domain : proto::domain< proto::generator<calculator> > {}; int main() { calculator< proto::terminal< placeholder<0> >::type > const _1 = {{{}}}; calculator< proto::terminal< placeholder<1> >::type > const _2 = {{{}}}; std::cout << ((_1 + _2)(45., 56.)) << std::endl; } -------------------------------- END CODE -------------------------------- The error is: 1>using typeof emulation 1>C:\Program Files (x86)\boost_1_38_0\boost/proto/generate.hpp(153): error: no suitable user-defined conversion from "const boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>> &, const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>> &>, 2L>" to 1> "calculator<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>> &, const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>> &>, 2L>>" exists 1> return Extends<Expr>(expr); 1> ^ 1> detected during: 1> instantiation of "Extends<Expr> boost::proto::generatorns_::generator<Extends>::operator()(const Expr &) const [with Extends=calculator, Expr=boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>> &, const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>> &>, 2L>]" at 1> line 145 of "C:\Program Files (x86)\boost_1_38_0\boost/proto/operators.hpp" 1> instantiation of "Left::proto_domain::result<void (boost::proto::exprns_::expr<Tag, boost::proto::argsns_::list2<Left &, Right &>, boost::proto::argsns_::list2<Left &, Right &>::arity>)>::type boost::proto::detail::as_expr_if<Tag, Left, Right, Left::proto_is_expr_, Right::proto_is_expr_>::make(Left &, Right &) [with Tag=boost::proto::tag::plus, Left=const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>>, 1> Right=const calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>>]" at line 290 of "C:\Program Files (x86)\boost_1_38_0\boost/proto/operators.hpp" 1> instantiation of "const boost::proto::detail::as_expr_if<boost::proto::tag::plus, const Left, const Right, void, void>::type boost::proto::exprns_::operator+(const Left &, const Right &) [with Left=calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<0>>, 0L>>, Right=calculator<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1>>, 0L>>]" at line 120 of ".\Test4.cpp" 1> 1>compilation aborted for .\Test4.cpp (code 2)