I wrote the following functor:
struct ASCII_lower { template< typename CharT > CharT operator() (const CharT& ch) const { if (ch >= 'A' && ch <= 'Z') return ch+0x20; return ch; // unchanged } };
and when I used it to create a transformed_range, I get an error that it doesn't find result_type in ASCII_lower. Since the return type depends on the argument, how could I declare a result_type?
And why do I need it? Lambda functions don't have it, and I thought it was fairly old fashioned and optional for helping figure out the result type if necessary.
In C++0x, it is not necessary to help the compiler figure out the return type of a functor in any way - it can do it using decltype. To enable this functionality in boost, you need to define the symbol BOOST_RESULT_OF_USE_DECLTYPE Regards, Nate.