* 27.0.60; Asymmetry between (days-to-time) and (time-to-days)
@ 2020-03-24 9:18 Kevin Liu
2020-03-24 16:51 ` Paul Eggert
0 siblings, 1 reply; 2+ messages in thread
From: Kevin Liu @ 2020-03-24 9:18 UTC (permalink / raw)
To: emacs-devel
The asymmetry between (days-to-time) and (time-to-days) is quite surprising:
(format-time-string "%Y" (days-to-time (time-to-days (current-time))))
"3989"
One could work around this by using (time-to-number-of-days) which uses
the epoch time like (days-to-time), but that itself is awkwardly
asymmetric as it returns a float, as well as the asymmetric naming.
It's probably unrealistic that any existing behavior be changed, but it
would at least be nice to have a builtin function that is the inverse of
(time-to-days). Org-mode, for example, seems to use the Gregorian
convention of (time-to-days) throughout, and to convert a (org-today) to
a time requires this mess:
(format-time-string "%Y" (days-to-time (- (org-today) 719162)))
"2020"
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: 27.0.60; Asymmetry between (days-to-time) and (time-to-days)
2020-03-24 9:18 27.0.60; Asymmetry between (days-to-time) and (time-to-days) Kevin Liu
@ 2020-03-24 16:51 ` Paul Eggert
0 siblings, 0 replies; 2+ messages in thread
From: Paul Eggert @ 2020-03-24 16:51 UTC (permalink / raw)
To: Kevin Liu; +Cc: emacs-devel
On 3/24/20 2:18 AM, Kevin Liu wrote:
> The asymmetry between (days-to-time) and (time-to-days) is quite surprising:
>
> (format-time-string "%Y" (days-to-time (time-to-days (current-time))))
> "3989"
Even if time-to-days and days-to-time were inverses, this usage would be dubious
since the conversion back and forth would discard the fractional date and that
could cause format-time-string to do the wrong thing when the timestamp was near
a year boundary in a non-UTC timezone.
> It's probably unrealistic that any existing behavior be changed, but it
> would at least be nice to have a builtin function that is the inverse of
> (time-to-days).
We could add an optional argument to days-to-time; if it's t then days-to-time
could add 719162 to its argument before converting (or whatever the magic number
happens to be; I didn't check this).
^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-03-24 9:18 27.0.60; Asymmetry between (days-to-time) and (time-to-days) Kevin Liu
2020-03-24 16:51 ` Paul Eggert
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