added format() methods for Date and Datetime

[eddelbuettel]

also rolled dev version in config.h

also adds operator<<() which doesn't seem to get picked up by compiler, ie we get the underlying date number or seconds since epoch.

[nathan-russell]

This looks good to me; my only suggestion would be possibly dropping the trailing << std::endl;, as there may be cases where the extra newline and call to flush is not desirable.

[eddelbuettel]

Thanks for looking at these. These were so far mostly for seeing what it would -- where I really want them is in the vector case of the new classes. And yes, the forced newline would be annoying there. For an individual item it may still make sense. Not sure yet how to balance it, and when to line break for vectors (every N maybe?).

[eddelbuettel]

Also annoying:

R> library(Rcpp)
R> cppFunction('void foo(Date d) { Rcpp::Rcout << d << std::endl; } ')
R> foo(Sys.Date())
17132
R> cppFunction('void bar(Date d) { Rcpp::Rcout << d.format() << std::endl; } ')
R> bar(Sys.Date())
2016-11-27
R>

I'd love for foo() to do what bar() does.

[eddelbuettel]

There is something else going on. I don't even think the new operator<<() gets called there.

[coatless]

Might be naive on my part, but: Rcpp::Rcout or Rcpp::Rstreambuf instead of std::ostream?

[eddelbuettel]

No, do a ag operator\<\< inside the repo directory. All operator<< go to ostream from which they get redirected.

But @dcdillon just reminded me that I can't do this as a member function. So it was a null-op ;-)

[nathan-russell]

I think foo is failing because operator double() is being called instead of operator<<. Changing the definition to this works for me:

        // inline std::ostream &operator<<(std::ostream & s) const {
        //     s << this->format() << std::endl;
        //     return s;
        // }
        friend std::ostream& operator<<(std::ostream& os, const Date& d) {
            os << d.format() << std::endl;
            return os;
        }

[eddelbuettel]

Yes, @dcdillon and I chatted about that. I now have this working

  // end of public block
  friend inline std::ostream &operator<<(std::ostream & s, const Date d);

  // outside class
    inline std::ostream &operator<<(std::ostream & os, const Date d) {
        os << d.format();
        return os;
    }

and that worketh even ;-)

R> library(Rcpp)
R> cppFunction('void foo(Date d) { Rcpp::Rcout << d << std::endl; } ')
R> foo(Sys.Date())
2016-11-27
R>

[eddelbuettel]

If anybody else would like to 'bless' (or even "review") it I'd feel better before merging my own PR :)

[kevinushey]

Should we check the return value of ::strftime() here? What happens to txt if the user passes in a fmt string not recognized by ::strftime()?

[eddelbuettel]

Then strftime() returns zero. I guess we could check and return an explicit std::string(""). Would be cleaner.

[kevinushey]

Since txt isn't zero-initialized (it's a plain C array), it seems like it could be possible that no null byte exists at the end of txt. Or does ::strftime() write a null byte at the end? What if the output of ::strftime() doesn't fit in txt?

[eddelbuettel]

Per previous point and man strftime, by catching a return of zero we should catch that.

[kevinushey]

Similar questions here re: zero-initialization, checking of return value?

[kevinushey]

Some paranoid checks re: state of the char array used in conjunction with ::strftime() but otherwise LGTM.

[eddelbuettel]

Thanks, @kevinushey . I extended both format() functions to be a wee bit more explicit on the return values.

[kevinushey]

Okay, LGTM!

[eddelbuettel]

Thank you. I just added two (small) sets of unit tests which I'll in a minute and then I'll merge.