Elixir v1.9.2 Date View Source
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
(see Kernel.sigil_D/2
) 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 third-party calendar libraries.
Comparing dates
Comparisons in Elixir using ==/2
, >/2
, </2
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).
Link to this section Summary
Functions
Adds the number of days to the given date
.
Compares two date structs.
Converts the given date
from its calendar to the given calendar
.
Similar to Date.convert/2
, but raises an ArgumentError
if the conversion between the two calendars is not possible.
Calculates the day-of-era and era for a given
calendar date
.
Calculates the day of the week of a given date
.
Calculates the day of the year of a given date
.
Returns the number of days in the given date
month.
Calculates the difference between two dates, in a full number of days.
Converts an Erlang date tuple to a Date
struct.
Converts an Erlang date tuple but raises for invalid dates.
Parses the extended "Dates" format described by ISO 8601:2004.
Parses the extended "Dates" format described by ISO 8601:2004.
Returns true
if the year in the given date
is a leap year.
Returns the number of months in the given date
year.
Builds a new ISO date.
Calculates the quarter of the year of a given date
.
Returns a range of dates.
Converts the given date
to an Erlang date tuple.
Converts the given date
to
ISO 8601:2004.
Converts the given date to a string according to its calendar.
Returns the current date in UTC.
Calculates the year-of-era and era for a given calendar year.
Link to this section Types
Specs
t() :: %Date{ calendar: Calendar.calendar(), day: Calendar.day(), month: Calendar.month(), year: Calendar.year() }
Link to this section Functions
Specs
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]
iex> Date.add(~D[-0010-01-01], -2)
~D[-0011-12-30]
Specs
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
Specs
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}}
Specs
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}
Specs
day_of_era(Calendar.date()) :: {Calendar.day(), non_neg_integer()}
Calculates the day-of-era and era for a given
calendar date
.
Returns a tuple {day, era}
representing the
day within the era and the era number.
Examples
iex> Date.day_of_era(~D[0001-01-01])
{1, 1}
iex> Date.day_of_era(~D[0000-12-31])
{1, 0}
Specs
day_of_week(Calendar.date()) :: Calendar.day()
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
iex> Date.day_of_week(~D[-0015-10-30])
3
Specs
day_of_year(Calendar.date()) :: Calendar.day()
Calculates the day of the year of a given date
.
Returns the day of the year as an integer. For the ISO 8601 calendar (the default), it is an integer from 1 to 366.
Examples
iex> Date.day_of_year(~D[2016-01-01])
1
iex> Date.day_of_year(~D[2016-11-01])
306
iex> Date.day_of_year(~D[-0015-10-30])
303
iex> Date.day_of_year(~D[2004-12-31])
366
Specs
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
Specs
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[0000-01-02], ~D[-0001-12-30])
3
iex> Date.diff(~D[2000-01-01], ~N[2000-01-03 09:00:00])
-2
Specs
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}
Specs
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
Specs
from_iso8601(String.t(), Calendar.calendar()) :: {:ok, t()} | {:error, atom()}
Parses the extended "Dates" format described by ISO 8601:2004.
The year parsed by this function is limited to four digits.
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}
Specs
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
Specs
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
Specs
months_in_year(Calendar.date()) :: Calendar.month()
Returns the number of months in the given date
year.
Example
iex> Date.months_in_year(~D[1900-01-13])
12
Specs
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}
Specs
quarter_of_year(Calendar.date()) :: non_neg_integer()
Calculates the quarter of the year of a given date
.
Returns the day of the year as an integer. For the ISO 8601 calendar (the default), it is an integer from 1 to 4.
Examples
iex> Date.quarter_of_year(~D[2016-10-31])
4
iex> Date.quarter_of_year(~D[2016-01-01])
1
iex> Date.quarter_of_year(~N[2016-04-01 01:23:45])
2
iex> Date.quarter_of_year(~D[-0015-09-30])
3
Specs
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
Specs
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}
Specs
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"
Specs
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"
iex> Date.to_string(~D[-0100-12-15])
"-0100-12-15"
Specs
utc_today(Calendar.calendar()) :: t()
Returns the current date in UTC.
Examples
iex> date = Date.utc_today()
iex> date.year >= 2016
true
Specs
year_of_era(Calendar.date()) :: {Calendar.year(), non_neg_integer()}
Calculates the year-of-era and era for a given calendar year.
Returns a tuple {year, era}
representing the
year within the era and the era number.
Examples
iex> Date.year_of_era(~D[0001-01-01])
{1, 1}
iex> Date.year_of_era(~D[0000-12-31])
{1, 0}
iex> Date.year_of_era(~D[-0001-01-01])
{2, 0}