Thorsten Ottosen wrote:
Hi Joel,
"Joel de Guzman" <joel@boost-consulting.com> wrote in message news:40B57D2D.6070905@boost-consulting.com...
| > 2. if we shouldn't copy a rule, why is copying not disabled? It has been a source of errors in my code that | > I forgot & on my return value. | | I believe http://www.boost.org/libs/spirit/doc/stored_rule.html | answers this question.
"The rule is a wierd C++ citizen, unlike any other C++ object. It does not have the proper copy and assignment semantics and cannot be stored and passed around by value. You cannot store rules in STL containers (vector, stack, etc) for later use and you cannot pass and return rules to and from functions by value."
I have read this page before, but I still don't get why the rule has copy and assignment semantics at all. Afterall, you admit copying and assignment does not make sense, yet it is still defined :-) What am I overlooking? Why do we need the current copy/assignment semantics?
Copy and assignment does not make sense. However, the = makes sense, yet, not in the C++ sense. Consider: rule<> a = x; or: rule<> a; a = x; How should this behave if x is an int_p? Now how should it behave if x is another rule? Consider a concrete example (snipped from the pascal parser): rule<> identifier; rule<> fileIdentifier; identifier = .... fileIdentifier = identifier; // an alias -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net