Date
A Date struct and functions.
The Date struct contains the fields year, month, day and calendar. New dates can be built with the new/3
function or using the ~D
sigil:
iex> ~D[2000-01-01] ~D[2000-01-01]
Both new/3
and sigil return a struct where the date fields can be accessed directly:
iex> date = ~D[2000-01-01] iex> date.year 2000 iex> date.month 1
The functions on this module work with the Date
struct as well as any struct that contains the same fields as the Date
struct, such as NaiveDateTime
and DateTime
. Such functions expect Calendar.date/0
in their typespecs (instead of t/0
).
Developers should avoid creating the Date structs directly and instead rely on the functions provided by this module as well as the ones in 3rd party calendar libraries.
Comparing dates
Comparisons in Elixir using ==
, >
, <
and similar are structural and based on the Date
struct fields. For proper comparison between dates, use the compare/2
function.
Using epochs
The add/2
and diff/2
functions can be used for computing dates or retrieving the number of days between instants. For example, if there is an interest in computing the number of days from the Unix epoch (1970-01-01):
iex> Date.diff(~D[2010-04-17], ~D[1970-01-01]) 14716 iex> Date.add(~D[1970-01-01], 14716) ~D[2010-04-17]
Those functions are optimized to deal with common epochs, such as the Unix Epoch above or the Gregorian Epoch (0000-01-01).
Summary
Types
Functions
- add(date, days)
-
Adds the number of days to the given
date
- compare(date1, date2)
-
Compares two date structs
- convert(date, calendar)
-
Converts the given
date
from its calendar to the givencalendar
- convert!(date, calendar)
-
Similar to
Date.convert/2
, but raises anArgumentError
if the conversion between the two calendars is not possible - day_of_week(date)
-
Calculates the day of the week of a given
date
- days_in_month(date)
-
Returns the number of days in the given
date
month - diff(date1, date2)
-
Calculates the difference between two dates, in a full number of days
- from_erl(tuple, calendar \\ Calendar.ISO)
-
Converts an Erlang date tuple to a
Date
struct - from_erl!(tuple, calendar \\ Calendar.ISO)
-
Converts an Erlang date tuple but raises for invalid dates
- from_iso8601(string, calendar \\ Calendar.ISO)
-
Parses the extended “Dates” format described by ISO 8601:2004
- from_iso8601!(string, calendar \\ Calendar.ISO)
-
Parses the extended “Dates” format described by ISO 8601:2004
- leap_year?(date)
-
Returns true if the year in the given
date
is a leap year - new(year, month, day, calendar \\ Calendar.ISO)
-
Builds a new ISO date
- range(first, last)
-
Returns a range of dates
- to_erl(date)
-
Converts the given
date
to an Erlang date tuple - to_iso8601(date, format \\ :extended)
-
Converts the given
date
to ISO 8601:2004 - to_string(date)
-
Converts the given date to a string according to its calendar
- utc_today(calendar \\ Calendar.ISO)
-
Returns the current date in UTC
Types
t()
t() :: %Date{ calendar: Calendar.calendar(), day: Calendar.day(), month: Calendar.month(), year: Calendar.year() }
Functions
add(date, days)
add(Calendar.date(), integer()) :: t()
Adds the number of days to the given date
.
The days are counted as Gregorian days. The date is returned in the same calendar as it was given in.
Examples
iex> Date.add(~D[2000-01-03], -2) ~D[2000-01-01] iex> Date.add(~D[2000-01-01], 2) ~D[2000-01-03] iex> Date.add(~N[2000-01-01 09:00:00], 2) ~D[2000-01-03]
compare(date1, date2)
compare(Calendar.date(), Calendar.date()) :: :lt | :eq | :gt
Compares two date structs.
Returns :gt
if first date is later than the second and :lt
for vice versa. If the two dates are equal :eq
is returned.
Examples
iex> Date.compare(~D[2016-04-16], ~D[2016-04-28]) :lt
This function can also be used to compare across more complex calendar types by considering only the date fields:
iex> Date.compare(~D[2016-04-16], ~N[2016-04-28 01:23:45]) :lt iex> Date.compare(~D[2016-04-16], ~N[2016-04-16 01:23:45]) :eq iex> Date.compare(~N[2016-04-16 12:34:56], ~N[2016-04-16 01:23:45]) :eq
convert(date, calendar)
convert(Calendar.date(), Calendar.calendar()) :: {:ok, t()} | {:error, :incompatible_calendars}
Converts the given date
from its calendar to the given calendar
.
Returns {:ok, date}
if the calendars are compatible, or {:error, :incompatible_calendars}
if they are not.
See also Calendar.compatible_calendars?/2
.
Examples
Imagine someone implements Calendar.Holocene
, a calendar based on the Gregorian calendar that adds exactly 10,000 years to the current Gregorian year:
iex> Date.convert(~D[2000-01-01], Calendar.Holocene) {:ok, %Date{calendar: Calendar.Holocene, year: 12000, month: 1, day: 1}}
convert!(date, calendar)
convert!(Calendar.date(), Calendar.calendar()) :: t()
Similar to Date.convert/2
, but raises an ArgumentError
if the conversion between the two calendars is not possible.
Examples
Imagine someone implements Calendar.Holocene
, a calendar based on the Gregorian calendar that adds exactly 10,000 years to the current Gregorian year:
iex> Date.convert!(~D[2000-01-01], Calendar.Holocene) %Date{calendar: Calendar.Holocene, year: 12000, month: 1, day: 1}
day_of_week(date)
day_of_week(Calendar.date()) :: non_neg_integer()
Calculates the day of the week of a given date
.
Returns the day of the week as an integer. For the ISO 8601 calendar (the default), it is an integer from 1 to 7, where 1 is Monday and 7 is Sunday.
Examples
iex> Date.day_of_week(~D[2016-10-31]) 1 iex> Date.day_of_week(~D[2016-11-01]) 2 iex> Date.day_of_week(~N[2016-11-01 01:23:45]) 2
days_in_month(date)
days_in_month(Calendar.date()) :: Calendar.day()
Returns the number of days in the given date
month.
Examples
iex> Date.days_in_month(~D[1900-01-13]) 31 iex> Date.days_in_month(~D[1900-02-09]) 28 iex> Date.days_in_month(~N[2000-02-20 01:23:45]) 29
diff(date1, date2)
diff(Calendar.date(), Calendar.date()) :: integer()
Calculates the difference between two dates, in a full number of days.
It returns the number of Gregorian days between the dates. Only Date
structs that follow the same or compatible calendars can be compared this way. If two calendars are not compatible, it will raise.
Examples
iex> Date.diff(~D[2000-01-03], ~D[2000-01-01]) 2 iex> Date.diff(~D[2000-01-01], ~D[2000-01-03]) -2 iex> Date.diff(~D[2000-01-01], ~N[2000-01-03 09:00:00]) -2
from_erl(tuple, calendar \\ Calendar.ISO)
from_erl(:calendar.date(), Calendar.calendar()) :: {:ok, t()} | {:error, atom()}
Converts an Erlang date tuple to a Date
struct.
Only supports converting dates which are in the ISO calendar, or other calendars in which the days also start at midnight. Attempting to convert dates from other calendars will return an error tuple.
Examples
iex> Date.from_erl({2000, 1, 1}) {:ok, ~D[2000-01-01]} iex> Date.from_erl({2000, 13, 1}) {:error, :invalid_date}
from_erl!(tuple, calendar \\ Calendar.ISO)
from_erl!(:calendar.date(), Calendar.calendar()) :: t()
Converts an Erlang date tuple but raises for invalid dates.
Examples
iex> Date.from_erl!({2000, 1, 1}) ~D[2000-01-01] iex> Date.from_erl!({2000, 13, 1}) ** (ArgumentError) cannot convert {2000, 13, 1} to date, reason: :invalid_date
from_iso8601(string, calendar \\ Calendar.ISO)
from_iso8601(String.t(), Calendar.calendar()) :: {:ok, t()} | {:error, atom()}
Parses the extended “Dates” format described by ISO 8601:2004.
Examples
iex> Date.from_iso8601("2015-01-23") {:ok, ~D[2015-01-23]} iex> Date.from_iso8601("2015:01:23") {:error, :invalid_format} iex> Date.from_iso8601("2015-01-32") {:error, :invalid_date}
from_iso8601!(string, calendar \\ Calendar.ISO)
from_iso8601!(String.t(), Calendar.calendar()) :: t()
Parses the extended “Dates” format described by ISO 8601:2004.
Raises if the format is invalid.
Examples
iex> Date.from_iso8601!("2015-01-23") ~D[2015-01-23] iex> Date.from_iso8601!("2015:01:23") ** (ArgumentError) cannot parse "2015:01:23" as date, reason: :invalid_format
leap_year?(date)
leap_year?(Calendar.date()) :: boolean()
Returns true if the year in the given date
is a leap year.
Examples
iex> Date.leap_year?(~D[2000-01-01]) true iex> Date.leap_year?(~D[2001-01-01]) false iex> Date.leap_year?(~D[2004-01-01]) true iex> Date.leap_year?(~D[1900-01-01]) false iex> Date.leap_year?(~N[2004-01-01 01:23:45]) true
new(year, month, day, calendar \\ Calendar.ISO)
new(Calendar.year(), Calendar.month(), Calendar.day(), Calendar.calendar()) :: {:ok, t()} | {:error, atom()}
Builds a new ISO date.
Expects all values to be integers. Returns {:ok, date}
if each entry fits its appropriate range, returns {:error, reason}
otherwise.
Examples
iex> Date.new(2000, 1, 1) {:ok, ~D[2000-01-01]} iex> Date.new(2000, 13, 1) {:error, :invalid_date} iex> Date.new(2000, 2, 29) {:ok, ~D[2000-02-29]} iex> Date.new(2000, 2, 30) {:error, :invalid_date} iex> Date.new(2001, 2, 29) {:error, :invalid_date}
range(first, last)
range(Date.t(), Date.t()) :: Date.Range.t()
Returns a range of dates.
A range of dates represents a discrete number of dates where the first and last values are dates with matching calendars.
Ranges of dates can be either increasing (first <= last
) or decreasing (first > last
). They are also always inclusive.
Examples
iex> Date.range(~D[1999-01-01], ~D[2000-01-01]) #DateRange<~D[1999-01-01], ~D[2000-01-01]>
A range of dates implements the Enumerable
protocol, which means functions in the Enum
module can be used to work with ranges:
iex> range = Date.range(~D[2001-01-01], ~D[2002-01-01]) iex> Enum.count(range) 366 iex> Enum.member?(range, ~D[2001-02-01]) true iex> Enum.reduce(range, 0, fn _date, acc -> acc - 1 end) -366
to_erl(date)
to_erl(Calendar.date()) :: :calendar.date()
Converts the given date
to an Erlang date tuple.
Only supports converting dates which are in the ISO calendar, or other calendars in which the days also start at midnight. Attempting to convert dates from other calendars will raise.
Examples
iex> Date.to_erl(~D[2000-01-01]) {2000, 1, 1} iex> Date.to_erl(~N[2000-01-01 00:00:00]) {2000, 1, 1}
to_iso8601(date, format \\ :extended)
to_iso8601(Calendar.date(), :extended | :basic) :: String.t()
Converts the given date
to ISO 8601:2004.
By default, Date.to_iso8601/2
returns dates formatted in the “extended” format, for human readability. It also supports the “basic” format through passing the :basic
option.
Only supports converting dates which are in the ISO calendar, or other calendars in which the days also start at midnight. Attempting to convert dates from other calendars will raise an ArgumentError
.
Examples
iex> Date.to_iso8601(~D[2000-02-28]) "2000-02-28" iex> Date.to_iso8601(~D[2000-02-28], :basic) "20000228" iex> Date.to_iso8601(~N[2000-02-28 00:00:00]) "2000-02-28"
to_string(date)
to_string(Calendar.date()) :: String.t()
Converts the given date to a string according to its calendar.
Examples
iex> Date.to_string(~D[2000-02-28]) "2000-02-28" iex> Date.to_string(~N[2000-02-28 01:23:45]) "2000-02-28"
utc_today(calendar \\ Calendar.ISO)
utc_today(Calendar.calendar()) :: t()
Returns the current date in UTC.
Examples
iex> date = Date.utc_today() iex> date.year >= 2016 true
© 2012 Plataformatec
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/elixir/1.6.6/Date.html