It is worth noting that Date and friends in Elixir require a calendar
field, which is not present in Duration, and therefore Duration won't be
usable as Date (and friends).
The biggest question is if we consider the fields in Duration a unit or
not. If they are units, then the most consistent choice is to keep them
singular, to mirror System.time_unit and friends.
On Fri, Mar 8, 2024 at 4:55 AM Kip Cole <kipco...@gmail.com> wrote:
> In my head, a Date.t is semantically a duration. So it’s completely valid
> to pass it as a duration to Date.shift as I see it. Which argues for
> singular names.
>
> This conversation is a bit like “is a date a point in time or an
> interval”. And the answer is yes, depending.
>
> Sent from my iPhone
>
> On 8 Mar 2024, at 14:39, Sabiwara Yukichi <sabiw...@gmail.com> wrote:
>
>
> I'm personally leaning more towards the plural, because it feels
> semantically more correct to treat a point of time and a duration as
> separate.
>
> d.year means the same thing if d is either a date or a datetime, but for a
> duration calling it d.years emphasizes the difference.
>
> It could perhaps help catch errors as well, both for the human and the
> compiler.
> One (arguably contrived) example would be structurally typed code which
> doesn't enforce any type in particular but uses the dot access or partial
> pattern matches like %{year: ..., month: ...} in order to support both
> dates or datetimes. Passing in a duration wouldn't make sense semantically,
> having different names would make it fail properly.
>
> I also agree with other reasons mentioned, the known standard one
> especially.
>
> Le jeu. 7 mars 2024 à 16:07, 'Theo Fiedler' via elixir-lang-core <
> elixir-lang-core@googlegroups.com> a écrit :
>
>> Right, it would make using a Duration in combination with the `add/2-3`
>> functions much harder than it needs to be. So far all time units in Elixir
>> are singular, and I think we do gain something from consistently sticking
>> to that, regardless of the context of durations, calendar types and what
>> not.
>>
>> I've seen some libraries allowing both, singular and plural, which i dont
>> want to have anything to do with, except for mentioning it though haha.
>>
>> What i currently see is:
>>
>> Reasons for plural:
>> - Known standard across various libraries and programming languages
>> - Sounds natural, to shift a date by "3 months" instead of "3 month".
>>
>> Reasons for singular:
>> - Compatible with time units already defined in Elixir (also relevant for
>> extending the use of Duration later on)
>> - Reduced cognitive load as the time units are always spelled the same
>> regardless of the context
>>
>> The reasons for singular do outweigh the reasons for plural, so unless
>> we're making some very strong points for diverging from that, let's keep it
>> singular!
>>
>> On Thursday, March 7, 2024 at 7:39:15 AM UTC+1 José Valim wrote:
>>
>>> Compatibility with the other time units is an important point. My mind
>>> is back on singular again. :)
>>>
>>> On Thu, Mar 7, 2024 at 07:20 'Theo Fiedler' via elixir-lang-core <
>>> elixir-l...@googlegroups.com> wrote:
>>>
>>>> While i was strongly leaning towards singular, i understand why one
>>>> would expect plural. Given that seems to be pretty standard in wild, i am
>>>> fine changing it as well.
>>>>
>>>> What mostly put me off about was that we'd end up with `Time.add(t, 3,
>>>> :minute)` vs `Time.shift(t, minutes: 3)`, which after all, maybe isn't too
>>>> bad, as we can keep the plural keys exclusive to durations. Another reason
>>>> for going with plurals is that it _should_ make migrating from some
>>>> libraries to the standard library relatively straight forward (with the
>>>> exception of microseconds).
>>>>
>>>> On Wednesday, March 6, 2024 at 11:07:52 PM UTC+1 José Valim wrote:
>>>>
>>>>> After a quick glance on other programming languages, it seems Python,
>>>>> Java, Rust, and C# all have plural names. Erlang also uses plural in its
>>>>> helper functions in the timer module. So we might want to follow suit.
>>>>>
>>>>> On Wed, Mar 6, 2024 at 23:03 José Valim <jose....@dashbit.co> wrote:
>>>>>
>>>>>> We discussed plural vs singular and settled on singular so it mirrors
>>>>>> the calendar types. Thoughts?
>>>>>>
>>>>>> On Wed, Mar 6, 2024 at 23:01 Panagiotis Nezis <pne...@gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> +1 for this, awesome work Theo. Shifting dates/timestamps is such a
>>>>>>> common operation and a standard implementation would be beneficial for
>>>>>>> everybody.
>>>>>>>
>>>>>>> PS. I would expect plural in the duration fields.
>>>>>>>
>>>>>>> On Wed, Mar 6, 2024 at 8:23 PM José Valim <jose....@dashbit.co>
>>>>>>> wrote:
>>>>>>>
>>>>>> The main argument for having it in core is:
>>>>>>>>
>>>>>>>> * It integrates directly with the Calendar behaviour
>>>>>>>> * We could provide built-in sigils in the future to create
>>>>>>>> readable durations, such as ~P[3 hours and 10 minutes]
>>>>>>>> * Postgrex, Explorer, CLDR, etc all implement their own version
>>>>>>>> of durations
>>>>>>>>
>>>>>>>> Arguments for not having it in core: it happens that all of the
>>>>>>>> arguments above can also be solved without adding Duration to Elixir
>>>>>>>> and,
>>>>>>>> instead, by creating a custom library:
>>>>>>>>
>>>>>>>> * A separate library could extend the calendar behaviour with
>>>>>>>> shift_* functions
>>>>>>>> * Third-party sigils can also be provided by libraries
>>>>>>>> * Postgrex, Explorer, and CLDR could create or use a package with
>>>>>>>> a duratio type shared across them all
>>>>>>>>
>>>>>>>> I would love to hear the community thoughts.
>>>>>>>>
>>>>>>>> On Wed, Mar 6, 2024 at 7:16 PM 'Theo Fiedler' via elixir-lang-core <
>>>>>>>> elixir-l...@googlegroups.com> wrote:
>>>>>>>>
>>>>>>> *Preface*
>>>>>>>>>
>>>>>>>>> We currently have `add/2-3` to manipulate calendar types in the
>>>>>>>>> standard library. These functions allow adding a specified amount of
>>>>>>>>> time
>>>>>>>>> of given unit to a date/time. The standard library currently misses
>>>>>>>>> means
>>>>>>>>> to apply more complex, or logical *durations *to calendar types.
>>>>>>>>> e.g. adding a month, a week, or one month and 10 days to a date.
>>>>>>>>>
>>>>>>>>> *Reasons for it*
>>>>>>>>>
>>>>>>>>> While similar functionality exists in libraries, such as CLDR,
>>>>>>>>> Timex, Tox, adding this functionality to the standard library has
>>>>>>>>> already
>>>>>>>>> been requested and discussed at multiple occasions over the past
>>>>>>>>> years. To
>>>>>>>>> list a few examples:
>>>>>>>>>
>>>>>>>>> - https://github.com/elixir-lang/elixir/pull/10199
>>>>>>>>> -
>>>>>>>>> https://elixirforum.com/t/get-date-n-months-years-in-the-past/48346/3
>>>>>>>>> -
>>>>>>>>> https://elixir-lang.slack.com/archives/C0HEX82NR/p1709581478427009?thread_ts=1709368588.334759&cid=C0HEX82NR
>>>>>>>>>
>>>>>>>>> Furthermore the shift behaviour in the extremely popular library
>>>>>>>>> Timex changed <https://github.com/bitwalker/timex/issues/731> in
>>>>>>>>> Elixir >= 1.14.3 which may have complicated the mostly lean and
>>>>>>>>> non-breaking language upgrade Elixir has to offer.
>>>>>>>>>
>>>>>>>>> Elixir has a great set of modules and functions that deal with
>>>>>>>>> date and time, the APIs are consistent and `shift/2-3` should fit
>>>>>>>>> right in,
>>>>>>>>> solving many standard needs of various industries, be it for
>>>>>>>>> reporting,
>>>>>>>>> appointments, events, finance... the list goes on, engineers probably
>>>>>>>>> face
>>>>>>>>> the need to shift time logically more often than not in their careers.
>>>>>>>>>
>>>>>>>>> *Technical details*
>>>>>>>>>
>>>>>>>>> Duration
>>>>>>>>> A date or time must be shifted by a *duration*. There is an ISO8601
>>>>>>>>> for durations <https://en.wikipedia.org/wiki/ISO_8601#Durations>,
>>>>>>>>> which the initial implementation is loosely following. The structure
>>>>>>>>> of a
>>>>>>>>> Duration lives in its own module with its own set of functions to
>>>>>>>>> create
>>>>>>>>> and manipulate durations. One example of where it diverts from the ISO
>>>>>>>>> standard, is that it implements microseconds. Microseconds in a
>>>>>>>>> *duration* are stored in the same format as in the time calendar
>>>>>>>>> types, meaning they integrate well and provide consistency.
>>>>>>>>>
>>>>>>>>> Shift
>>>>>>>>> The shift behaviour is implemented as a callback on Calendar and
>>>>>>>>> supported by all calendar types: Date, DateTime, NaiveDateTime and
>>>>>>>>> Time.
>>>>>>>>> Date, Time and NaiveDateTime each have their own implementation of a
>>>>>>>>> "shift", while DateTime gets converted to a NaiveDateTime before
>>>>>>>>> applying
>>>>>>>>> the shift, and is then rebuilt to a DateTime in its original timezone.
>>>>>>>>> `shift/2-3` also has guaranteed output types (which isn't a given in
>>>>>>>>> many
>>>>>>>>> libraries) and follows the consistent API which is established in the
>>>>>>>>> calendar modules.
>>>>>>>>>
>>>>>>>>> Find the current state of the implementation here:
>>>>>>>>> https://github.com/elixir-lang/elixir/pull/13385
>>>>>>>>>
>>>>>>>>> *Benchmarks*
>>>>>>>>>
>>>>>>>>> There are some benchmarks + StreamData tests in the PR description.
>>>>>>>>>
>>>>>>>>> *Outlook*
>>>>>>>>>
>>>>>>>>> *After *adding the Duration type and shift behaviour to the
>>>>>>>>> standard library, the following things could be explored and derived
>>>>>>>>> from
>>>>>>>>> the initial work:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> - Implementing a protocol that allows Duration to be applied
>>>>>>>>> to any data type, not just dates and times.
>>>>>>>>> - A range-like data type that allows us to do recurring
>>>>>>>>> constructs on any data type. For example,
>>>>>>>>> Duration.interval(~D[2000-01-01],
>>>>>>>>> month: 1), when iterated, would emit {:ok, date} | {:error,
>>>>>>>>> start, duration, reason} entries
>>>>>>>>> - A sigil for easy creation of durations: ~P[3 hours and 10
>>>>>>>>> minutes]
>>>>>>>>> - Making it so add/2-3 reuses the shift_* functions
>>>>>>>>>
>>>>>>>>> *Reasons against it*
>>>>>>>>>
>>>>>>>>> While I am convinced that adding `shift/2-3` to the standard
>>>>>>>>> library would be very beneficial, nothing really speaks against the
>>>>>>>>> points
>>>>>>>>> mentioned above to be implemented in a library instead. However,
>>>>>>>>> something
>>>>>>>>> as crucial and central as date/time manipulation should still be part
>>>>>>>>> of
>>>>>>>>> the standard library, negating the risk of breaking changes,
>>>>>>>>> inconsistent
>>>>>>>>> behaviour and outdated or too unique ergonomics which aren't widely
>>>>>>>>> applicable, unlike what should be part of the standard library.
>>>>>>>>>
>>>>>>>>> Many thanks to @jose & @kip for the initial reviews and everyone
>>>>>>>>> in advance taking the time to read the proposal!
>>>>>>>>>
>>>>>>>>> Looking forward to hear other peoples ideas and opinions on the
>>>>>>>>> subject!
>>>>>>>>>
>>>>>>>>> --
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>>>>>>>>> Groups "elixir-lang-core" group.
>>>>>>>>>
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>>>>>>>>> send an email to elixir-lang-co...@googlegroups.com.
>>>>>>>>> To view this discussion on the web visit
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>>>>>>>>> .
>>>>>>>>
>>>>>>>>
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