You continue to astound me with your responsiveness, José. Thank you for
all you have done!
Truncating and zeroing out certainly are different things, and there's no
simple way to implement both perfectly. I would be thrilled to get some
improvement implemented, however the community decides is best.
I recommend against making perfect the enemy of the good. My hunch is that
many people seeking to zero out hours or minutes would go looking for the
`truncate/2` function and not even consider the difference. The distinction
between truncation (of sub-second values) and zeroing (of minutes and
seconds to truncate to the nearest hour or minute) could be
mentioned/explained in the function's @doc section.
Currently, `truncate/2` enables neither truncating nor zeroing out. If true
truncation is indeed a "large change" with significant downstream
implications for existing apps, as I'm sure it is, then it's probably not
something we'll ever want to implement. Providing the zeroing out
functionality inside `truncate/2` would give users the option to do so. It
wouldn't satisfy all use cases, but -- as you note -- true truncation is
arguably prohibitively impactful.
Cheers,
James
On Friday, January 26, 2024 at 11:39:12 AM UTC-5 José Valim wrote:
> This is complicated because "truncate" is about removing the precision,
> and we cannot have a minute precision. The way to support it properly would
> be to allow seconds to be nil and then we would print it as "2022-12-31
> 13:45", without the seconds component, but I think this would be a large
> change (and applications would need to deal with the fact seconds could be
> nil).
>
> Perhaps we could introduce another function to "zerofy" certain fields,
> while perhaps keeping precision. Although, in your case, the easiest is to
> truncate and then directly zerofy the fields in the struct.
>
> On Fri, Jan 26, 2024 at 5:27 PM James Lavin <coder.ja...@gmail.com> wrote:
>
>> Hi:
>>
>> Thank you, Elixir community, for building this incredible language and
>> ecosystem!
>>
>> I just had a need to truncate a NaiveDateTime to the nearest minute and
>> was surprised to see that option isn't available.
>>
>> I'd like to propose something like the following (which I just typed out
>> but haven't tested):
>>
>> ```
>> @doc """
>> Returns the given naive datetime truncated to the given precision
>> (`:microsecond`, `:millisecond`, `:second`, `:minute` or `:hour`).
>>
>> The given naive datetime is returned unchanged if it already has lower
>> precision
>> than the given precision.
>>
>> ## Examples
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456],
>> :microsecond)
>> ~N[2017-11-06 00:23:51.123456]
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456],
>> :millisecond)
>> ~N[2017-11-06 00:23:51.123]
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456], :second)
>> ~N[2017-11-06 00:23:51]
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456], :minute)
>> ~N[2017-11-06 00:23:00]
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456], :hour)
>> ~N[2017-11-06 00:00:00]
>>
>> """
>> @doc since: "1.6.0"
>> @spec truncate(t(), :microsecond | :millisecond | :second | :minute |
>> :hour) :: t()
>> def truncate(%NaiveDateTime{microsecond: microsecond} = naive_datetime,
>> :hour) do
>> %{naive_datetime | minute: 0, second: 0, microsecond:
>> Calendar.truncate(microsecond, :second)}
>> end
>>
>> def truncate(%NaiveDateTime{microsecond: microsecond} = naive_datetime,
>> :minute) do
>> %{naive_datetime | second: 0, microsecond:
>> Calendar.truncate(microsecond, :second)}
>> end
>>
>> def truncate(%NaiveDateTime{microsecond: microsecond} = naive_datetime,
>> precision) do
>> %{naive_datetime | microsecond: Calendar.truncate(microsecond,
>> precision)}
>> end
>> ```
>>
>> Thank you for considering this idea.
>>
>> Cheers,
>>
>> James Lavin
>>
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