+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.va...@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-lang-core@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! >> >> -- >> You received this message because you are subscribed to the Google Groups >> "elixir-lang-core" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to elixir-lang-core+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/elixir-lang-core/cb0ed628-3848-4de0-aa13-c0f4761e4d99n%40googlegroups.com >> <https://groups.google.com/d/msgid/elixir-lang-core/cb0ed628-3848-4de0-aa13-c0f4761e4d99n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "elixir-lang-core" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to elixir-lang-core+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4%2BNmFsMhbkRubMjnmM8c_Amq8DgmKCJtzJ1GEuM4-sVgw%40mail.gmail.com > <https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4%2BNmFsMhbkRubMjnmM8c_Amq8DgmKCJtzJ1GEuM4-sVgw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. 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