On Mon, 10 May 2004 14:00:41 +0100, Reece Dunn wrote
Is there a boost library that allows...
No, but there is a template in date_time that does something close. It's called constrained_value. http://www.crystalclearsoftware.com/libraries/gdtl/gdtl_ref_guide/classboost... When an out of range value is found during construction or assignment the config class on_error function is called. From there you can throw an exception or do whatever error handling you like: So in the case of date_time there are 2 steps: 1) define a unique exception type 2) use the simple_exception_policy helper to configure the constrained_value struct bad_month : public std::out_of_range { bad_month() : std::out_of_range(std::string("Month number is out of range 1..12")) {} }; //! Build a policy class for the greg_month_rep typedef CV::simple_exception_policy<unsigned short, 1, 12, bad_month> greg_month_policies; //! A constrained range that implements the gregorian_month rules typedef CV::constrained_value<greg_month_policies> greg_month_rep; Now the following code will throw bad_month exception: greg_month_rep m(13); //throws bad_month greg_month_rep m(0); //throws bad_month greg_month_rep m(12); //ok
you to specify the range that a number can take, e.g.
boost::range< int, 1, 12 > month;
generating an error on an invalid range, e.g.
month = 20; // [1] oops!
Also, is it possible to distinguish between a number literal like the above and a variable assignment, like:
month = m; // [2]
Not sure. constrained_value doesn't.
The logic behind this is to provide compile-time checks where possible, so [1] would produce a compile-time error and [2] would be a run-time error. You could also do something like:
inline char & string::operator[]( boost::range< int, 5, 10 > i ){ ... } // ... string s; s[ 1 ] = 'a'; // oops!
and
class date { boost::range< int, 1, 12 > month; public: inline date( boost::range< int, 1, 12 > m ): month( m ){} };
Exactly -- and your code isn't littered with all sorts of range checking logic... Jeff