Re: encode-time vs decode-time

[Paul Eggert <eggert@cs.ucla.edu>]

Adam Porter wrote:
> Forgive me for being late to this discussion.  After struggling with
> using and manipulating date/time values in Emacs, I came up with this:
> 
> https://github.com/alphapapa/ts.el

I looked briefly at it, and don't see any compatibility issues - not that I 
understand all the code, which depends on packages I don't use.

The code's comments say that format-time-string is too slow. What performance 
issues did you run into? At any rate I think you'll find that this:

   (string-to-number (format-time-string "%Y" (ts-unix struct)))

is more efficient written this way:

   (nth 5 (decode-time (ts-unix struct)))

and I expect you can speed up the code further by caching the entire result of 
decode-time instead of calling format-time-string for each component.

Also, the timestamp functions in Emacs 27 should simplify ts.el, once you can 
assume Emacs 27. For example, in Emacs 27 you can do something like this:

   (decoded-time-add X (make-decoded-time :year 10))

to add 10 years to a broken-down timestamp X.

One more thing: ts.el's extensive use of float-time is fine for calendrical 
applications but has limited resolution (2**-22 s or about 2e-7 s for today's 
timestamps) and so would be problematic for apps requiring higher-resolution 
timestamps.