Eric Niebler wrote:
Michael Goldshteyn wrote:
Perhaps something like unfilled(), bare(), or as you suggested is_invalid() should be added to the actual implementation, instead of user code? I would further argue that something so trivial and tightly coupled to the implementation (i.e., regex_id() being zero) should be a member function and not stand alone.
What is it about checking the regex_id() that bothers you? Is it the constant 0? You could instead write it like ...
if(rex.regex_id() == sregex().regex_id())
Default-constructing a regex is very cheap, FWIW.
I'm not very familiar with xpressive, but having a look from aside it would never come into my mind that "rex.regex_id() == 0" is an emptyness (or whatever) check. Sorry, this looks more like a hack to me. I think a clear statement is needed: is a default-constructed regex valid? If not, then why does it have a default constructor? If it is, the default-constructed state should be easily detectable, since this is a common practice in just about any domain: - Boost.Regex, containers, strings, Boost.Function provide empty() - Boost.Optional, Boost.SmartPtr provide unspecified bool conversions and operator!, or equivalent facilities. Personally, I like empty() naming, but if a more precise name can be found, I would be fine. And I agree with Michael, such a function should be a member of the class. As for application, the empty state of regex may be useful when the expression may, or may not be compiled. It's a sort of implicit optional, but a simpler and more efficient one. However, I'm sure it's not the only valid use case.