Proposal for custom time string formatting in std.datetime

[Jonathan M Davis]

On Friday, December 23, 2011 12:02:26 Stewart Gordon wrote:
> What is the use case for including a full date in some externally defined
> format within a longer formatted date string?  ISTM the way to do this is
> to define a function that just generates this format straight off.  In my
> library, toShortFormatString and toLongFormatString are already examples of
> this.
>
> > It also means that you can't reuse letters.
> 
> At the moment only 12 letters are used.  I can't see the whole alphabet
> being used up any time in the foreseeable future.

It's not that I want to put %ctime and %mpeg7 in the same string. It's that I 
don't want to have to go define a function for every single one of them. It's a 
much smaller hit to the API to have flags for them.

Another alternative is to supply an enum of format strings for a variety of 
formats, though that also expands the API a bit (not as badly much though). 
That may a be better approach for known formats. That doesn't work as well 
though in cases where the format strings to toCustomString and 
fromCustomString aren't identical (which happens in the case of mpeg-7, since 
it uses %cond). So, I don't know. Regardless, I think that the abliity to have 
more or less arbitrary strings used for flags is valuable.

> I think I could expand my scheme to include ISO signed-year notation easily
> enough.  In the mpeg-7 standard, does the denominator of the fractional
> second have to be the smallest possible power of 10, or is F20/1000 or
> F0/1000 allowed just as well?

If it's 0, there is no fraction, just like there's no decimal if it's 0 for 
ISO. I don't _think_ that it has to be the smallest possible power of 10, but 
I don't remember at the moment. I'm going to have to track down the info on 
the spec again. I'd figured it out for work previously, but unfortunately I 
lost whatever bookmarks I had with the info.

I don't want to shell out money for the spec if I don't have to. Even if I 
were willing to buy it, it's sold in 12 parts, and I'd probably end up buying 
several parts before I found the one with the definition of its time format, 
wasting that much more money. So, I'll have to go digging online again.

- Jonathan M Davis