2011/5/2 alfC

Hi, Does Phoenix support conditional expression? I know if supports if_ *statements* but it seems that there's is no conditional (expression*. The question what is is the equivalent for

"(x>2.)?(1.):(-1.)"

in general. For example, I tryed with if_[].else_[] hoping that the statement is used as result but with no luck:

#include #include<iostream> using namespace boost::phoenix; using namespace boost::phoenix::arg_names; int main(){ std::clog << (arg1*arg1)(2.) << std::endl; //returns correctly 4 std::clog << (if_(arg1>2.)[val(1.)].else_[val(-1.)])(2.) << std::endl; //syntax error return 0; }

The syntax error points that the expression fails to evaluate as a number. Any ideas? -- Thanks, Alfredo

See: http://tinyurl.com/4xqsezx simply: std::clog << if_else(arg1>2., 1., -1.)(2.) << std::endl; HTH

On Mon, May 2, 2011 at 11:58 AM, alfC wrote:

Hi,  Does Phoenix support conditional expression? I know if supports if_ *statements* but it seems that there's is no conditional (expression*. The question what is is the equivalent for

 "(x>2.)?(1.):(-1.)"

in general. For example, I tryed with if_[].else_[] hoping that the statement is used as result but with no luck:

#include #include<iostream> using namespace boost::phoenix; using namespace boost::phoenix::arg_names; int main(){        std::clog << (arg1*arg1)(2.) << std::endl; //returns correctly 4        std::clog <<                (if_(arg1>2.)[val(1.)].else_[val(-1.)])(2.)         << std::endl; //syntax error        return 0; }

The syntax error points that the expression fails to evaluate as a number. Any ideas? -- Thanks, Alfredo

if_(...)[...] and if_(...)[...].else_[...] always return void. This is the problem you are seeing. There is a solution to this problem: http://goo.gl/gjH7F ... if_else(arg1 > 2., val(1.), val(-1.)) ... Regards, Thomas