[C++-sig] question on object section of bpl tutorial

[David Abrahams]

Mark Russell <mrussell8081 at pacbell.net> writes:

> // buffstr.cpp
>
> #include "disablewarnings.h"
> #include <boost/python.hpp>
> #include <string>
>
> using namespace boost::python;
> //keeps msvc happy
> #define STR boost::python::str

I prefer to eschew macros where possible, especially in tutorial examples.

> #define STR_BASE boost::python::detail::str_base

Ooh, you shouldn't touch this.  You shouldn't touch _anything_ in
namespace boost::python::detail!  That's why it's not documented.

> class BuffStr : public STR_BASE {
> public:
> 	BuffStr(STR word) : STR_BASE(word) { count(word); }
> 	int required;
> 	std::string repr_() {
> 		std::string rtnstr = extract<std::string>(*this);
> 		return "'" + rtnstr + "'";
> 	}
> 	std::string str_() {
> 		std::string req = boost::lexical_cast<std::string>(required);
> 		std::string rtnstr = extract<std::string>(*this);
> 		return "string: " + rtnstr + " --> required buf space: " + req;
> 	}
> private:
> 	void count(STR word) {
> 		required = 4 * extract<int>(word.attr("__len__")()) + 16;
> 	}
> };

What are you trying to accomplish by deriving from str_base?
Why not just store a str data member?

> list f(list x, BuffStr y) {
> 	if(y.required <= 56) 
> 		x.append(y);
> 	else
> 		x.append("too big");
> 	return x;
> }
>
> BOOST_PYTHON_MODULE(buffstr) {
> 	class_<BuffStr>("BuffStr", init<STR>())
> 		.def_readonly("required", &BuffStr::required)
> 		.def("__repr__", &BuffStr::repr_)
> 		.def("__str__", &BuffStr::str_);
>
> 	def("f", f);
> }

Hmm, I'm not convinced this one is ready for prime-time.  If it's
supposed to be a replacement for the original example, I'd really like
to see more of the variety of object operations exploited.

-Dave

-- 
                       David Abrahams
   dave at boost-consulting.com * http://www.boost-consulting.com
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