Proposal for custom time string formatting in std.datetime

[Brad Anderson]

On Wed, Dec 21, 2011 at 8:41 PM, Jonathan M Davis <jmdavisProg at gmx.com>wrote:

> Okay. At the moment, the time point types in std.datetime have functions
> for
> converting to and from strings of standard formats but not custom formats,
> so
> functions for that need to be added. I've come up with a proposal for how
> they're going to work and would like some feedback on it.
>
> Originally, I was going to make them work like strftime and strptime,
> since it
> was my understanding that those functions were fairly standard among
> various
> programming languags. And it _does_ look like a variety of programming
> languages have something similar (Java, Ruby, Python, etc.), but the exact
> set
> of flags that they use is not standard, so there _isn't_ really a standard
> to
> follow, just similar functions across a variety of programming languages.
> And
> honestly, strftime and strptime aren't very good. They're fairly limited
> IMHO,
> and the choice of flags is fairly arbitrary, so it seems like a good idea
> to
> design our own, assuming that we can make something better.
>
> Stewart Gordon has a library that takes a different approach (
> http://pr.stewartsplace.org.uk/d/sutil/datetime_format.html ). It does
> away
> with % flags and uses maximul munch with each of the flags being name such
> that
> they don't overlap in a way that would make certain combinations of flags
> impossible. It then requires that characters which are not part of the
> flags be
> surrounded by single quotes. It's an interesting approach, but it isn't as
> flexible as it could be because of its use of maximul munch instead of %
> flags.
>
> So, I've come up with something new which tries to take the best of both.
> On
> the whole, I think that it's fairly straightforward, and the flags are
> generally recognizable and memorable (though there are a lot). It's also
> definitely extremely flexible (e.g. you can pass it functions to generate
> portions of the string if the existing flags don't get you quite what you
> need). But I'd like some feedback on it before I spend a lot of time on the
> implementation.
>
> This page has the docs for std.datetime with everything else but the
> proposed
> custom formatting functions for SysTime stripped out of it:
>
> http://jmdavis.github.com/d-programming-language.org/std_datetime.html
>
> So, what do you think?
>
> - Jonathan M Davis
>


I must admit, I was scared by the first couple of examples on that page.
 It looks like the the general use case is more approachable though.  I've
never been much of a fan of strftime as I have to look up the syntax every
time I use it (despite writing date scheduling software for a living) and
it's difficult to look up because most languages use that name but often
have variants to the flags (as you've said) and they all show up in a
google search.  That said, it works and I wouldn't be upset if D ended up
using it.

Personally, I don't know that phobos needs a highly advanced data
formatting syntax built in. I kind of lean toward as simple of syntax as we
can get that covers 99% of what people need and maybe have something like
this offered as an third-party library for people who need its advanced
features. I do think Stewart Gordon's approach is a good fit for this
requirement.

In any case, I like how much thought you've put into this.

Regards,
Brad
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