# <!-- rdoc-file=ext/date/date_core.c -->
# date and datetime class - Tadayoshi Funaba 1998-2011
#
# 'date' provides two classes: Date and DateTime.
#
# ## Terms and Definitions
#
# Some terms and definitions are based on ISO 8601 and JIS X 0301.
#
# ### Calendar Date
#
# The calendar date is a particular day of a calendar year, identified by its
# ordinal number within a calendar month within that year.
#
# In those classes, this is so-called "civil".
#
# ### Ordinal Date
#
# The ordinal date is a particular day of a calendar year identified by its
# ordinal number within the year.
#
# In those classes, this is so-called "ordinal".
#
# ### Week Date
#
# The week date is a date identified by calendar week and day numbers.
#
# The calendar week is a seven day period within a calendar year, starting on a
# Monday and identified by its ordinal number within the year; the first
# calendar week of the year is the one that includes the first Thursday of that
# year. In the Gregorian calendar, this is equivalent to the week which includes
# January 4.
#
# In those classes, this is so-called "commercial".
#
# ### Julian Day Number
#
# The Julian day number is in elapsed days since noon (Greenwich Mean Time) on
# January 1, 4713 BCE (in the Julian calendar).
#
# In this document, the astronomical Julian day number is the same as the
# original Julian day number. And the chronological Julian day number is a
# variation of the Julian day number. Its days begin at midnight on local time.
#
# In this document, when the term "Julian day number" simply appears, it just
# refers to "chronological Julian day number", not the original.
#
# In those classes, those are so-called "ajd" and "jd".
#
# ### Modified Julian Day Number
#
# The modified Julian day number is in elapsed days since midnight (Coordinated
# Universal Time) on November 17, 1858 CE (in the Gregorian calendar).
#
# In this document, the astronomical modified Julian day number is the same as
# the original modified Julian day number. And the chronological modified Julian
# day number is a variation of the modified Julian day number. Its days begin at
# midnight on local time.
#
# In this document, when the term "modified Julian day number" simply appears,
# it just refers to "chronological modified Julian day number", not the
# original.
#
# In those classes, those are so-called "amjd" and "mjd".
#
# ## Date
#
# A subclass of Object that includes the Comparable module and easily handles
# date.
#
# A Date object is created with Date::new, Date::jd, Date::ordinal,
# Date::commercial, Date::parse, Date::strptime, Date::today, Time#to_date, etc.
#
#     require 'date'
#
#     Date.new(2001,2,3)
#      #=> #<Date: 2001-02-03 ...>
#     Date.jd(2451944)
#      #=> #<Date: 2001-02-03 ...>
#     Date.ordinal(2001,34)
#      #=> #<Date: 2001-02-03 ...>
#     Date.commercial(2001,5,6)
#      #=> #<Date: 2001-02-03 ...>
#     Date.parse('2001-02-03')
#      #=> #<Date: 2001-02-03 ...>
#     Date.strptime('03-02-2001', '%d-%m-%Y')
#      #=> #<Date: 2001-02-03 ...>
#     Time.new(2001,2,3).to_date
#      #=> #<Date: 2001-02-03 ...>
#
# All date objects are immutable; hence cannot modify themselves.
#
# The concept of a date object can be represented as a tuple of the day count,
# the offset and the day of calendar reform.
#
# The day count denotes the absolute position of a temporal dimension. The
# offset is relative adjustment, which determines decoded local time with the
# day count. The day of calendar reform denotes the start day of the new style.
# The old style of the West is the Julian calendar which was adopted by Caesar.
# The new style is the Gregorian calendar, which is the current civil calendar
# of many countries.
#
# The day count is virtually the astronomical Julian day number. The offset in
# this class is usually zero, and cannot be specified directly.
#
# A Date object can be created with an optional argument, the day of calendar
# reform as a Julian day number, which should be 2298874 to 2426355 or
# negative/positive infinity. The default value is `Date::ITALY`
# (2299161=1582-10-15). See also sample/cal.rb.
#
#     $ ruby sample/cal.rb -c it 10 1582
#         October 1582
#      S  M Tu  W Th  F  S
#         1  2  3  4 15 16
#     17 18 19 20 21 22 23
#     24 25 26 27 28 29 30
#     31
#
#     $ ruby sample/cal.rb -c gb  9 1752
#        September 1752
#      S  M Tu  W Th  F  S
#            1  2 14 15 16
#     17 18 19 20 21 22 23
#     24 25 26 27 28 29 30
#
# A Date object has various methods. See each reference.
#
#     d = Date.parse('3rd Feb 2001')
#                                  #=> #<Date: 2001-02-03 ...>
#     d.year                       #=> 2001
#     d.mon                        #=> 2
#     d.mday                       #=> 3
#     d.wday                       #=> 6
#     d += 1                       #=> #<Date: 2001-02-04 ...>
#     d.strftime('%a %d %b %Y')    #=> "Sun 04 Feb 2001"
#
class Date
  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - new(p1 = v1, p2 = v2, p3 = v3, p4 = v4)
  # -->
  #
  def initialize: (?Integer year, ?Integer month, ?Integer mday, ?Integer start) -> void

  include Comparable

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._httpdate(string, limit: 128)  ->  hash
  # -->
  # Returns a hash of parsed elements.
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self._httpdate: (String str) -> Hash[Symbol, Integer]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._iso8601(string, limit: 128)  ->  hash
  # -->
  # Returns a hash of parsed elements.
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self._iso8601: (String str) -> Hash[Symbol, Integer]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._jisx0301(string, limit: 128)  ->  hash
  # -->
  # Returns a hash of parsed elements.
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self._jisx0301: (String str) -> Hash[Symbol, Integer]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._parse(string[, comp=true], limit: 128)  ->  hash
  # -->
  # Parses the given representation of date and time, and returns a hash of parsed
  # elements.
  #
  # This method *does not* function as a validator.  If the input string does not
  # match valid formats strictly, you may get a cryptic result.  Should consider
  # to use `Date._strptime` or `DateTime._strptime` instead of this method as
  # possible.
  #
  # If the optional second argument is true and the detected year is in the range
  # "00" to "99", considers the year a 2-digit form and makes it full.
  #
  #     Date._parse('2001-02-03') #=> {:year=>2001, :mon=>2, :mday=>3}
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self._parse: (String str, ?boolish complete) -> Hash[Symbol, Integer]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._rfc2822(string, limit: 128)  ->  hash
  #   - Date._rfc822(string, limit: 128)   ->  hash
  # -->
  # Returns a hash of parsed elements.
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self._rfc2822: (String str) -> Hash[Symbol, Integer | String]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._rfc3339(string, limit: 128)  ->  hash
  # -->
  # Returns a hash of parsed elements.
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self._rfc3339: (String str) -> Hash[Symbol, Integer | String]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._rfc2822(string, limit: 128)  ->  hash
  #   - Date._rfc822(string, limit: 128)   ->  hash
  # -->
  # Returns a hash of parsed elements.
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self._rfc822: (String str) -> Hash[Symbol, Integer | String]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._strptime(string[, format='%F'])  ->  hash
  # -->
  # Parses the given representation of date and time with the given template, and
  # returns a hash of parsed elements.  _strptime does not support specification
  # of flags and width unlike strftime.
  #
  #     Date._strptime('2001-02-03', '%Y-%m-%d')
  #                               #=> {:year=>2001, :mon=>2, :mday=>3}
  #
  # See also strptime(3) and #strftime.
  #
  def self._strptime: (String str, ?String format) -> Hash[Symbol, Integer]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date._xmlschema(string, limit: 128)  ->  hash
  # -->
  # Returns a hash of parsed elements.
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self._xmlschema: (String str) -> Hash[Symbol, Integer]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.civil([year=-4712[, month=1[, mday=1[, start=Date::ITALY]]]])  ->  date
  #   - Date.new([year=-4712[, month=1[, mday=1[, start=Date::ITALY]]]])    ->  date
  # -->
  # Creates a date object denoting the given calendar date.
  #
  # In this class, BCE years are counted astronomically.  Thus, the year before
  # the year 1 is the year zero, and the year preceding the year zero is the year
  # -1.  The month and the day of month should be a negative or a positive number
  # (as a relative month/day from the end of year/month when negative).  They
  # should not be zero.
  #
  # The last argument should be a Julian day number which denotes the day of
  # calendar reform.  Date::ITALY (2299161=1582-10-15), Date::ENGLAND
  # (2361222=1752-09-14), Date::GREGORIAN (the proleptic Gregorian calendar) and
  # Date::JULIAN (the proleptic Julian calendar) can be specified as a day of
  # calendar reform.
  #
  #     Date.new(2001)            #=> #<Date: 2001-01-01 ...>
  #     Date.new(2001,2,3)        #=> #<Date: 2001-02-03 ...>
  #     Date.new(2001,2,-1)       #=> #<Date: 2001-02-28 ...>
  #
  # See also ::jd.
  #
  def self.civil: (?Integer year, ?Integer month, ?Integer mday, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.commercial([cwyear=-4712[, cweek=1[, cwday=1[, start=Date::ITALY]]]])  ->  date
  # -->
  # Creates a date object denoting the given week date.
  #
  # The week and the day of week should be a negative or a positive number (as a
  # relative week/day from the end of year/week when negative).  They should not
  # be zero.
  #
  #     Date.commercial(2001)     #=> #<Date: 2001-01-01 ...>
  #     Date.commercial(2002)     #=> #<Date: 2001-12-31 ...>
  #     Date.commercial(2001,5,6) #=> #<Date: 2001-02-03 ...>
  #
  # See also ::jd and ::new.
  #
  def self.commercial: (?Integer cwyear, ?Integer cweek, ?Integer cwday, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.gregorian_leap?(year)  ->  bool
  #   - Date.leap?(year)            ->  bool
  # -->
  # Returns true if the given year is a leap year of the proleptic Gregorian
  # calendar.
  #
  #     Date.gregorian_leap?(1900)        #=> false
  #     Date.gregorian_leap?(2000)        #=> true
  #
  def self.gregorian_leap?: (Integer year) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.httpdate(string='Mon, 01 Jan -4712 00:00:00 GMT'[, start=Date::ITALY], limit: 128)  ->  date
  # -->
  # Creates a new Date object by parsing from a string according to some RFC 2616
  # format.
  #
  #     Date.httpdate('Sat, 03 Feb 2001 00:00:00 GMT')
  #                                               #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self.httpdate: (String str, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.iso8601(string='-4712-01-01'[, start=Date::ITALY], limit: 128)  ->  date
  # -->
  # Creates a new Date object by parsing from a string according to some typical
  # ISO 8601 formats.
  #
  #     Date.iso8601('2001-02-03')        #=> #<Date: 2001-02-03 ...>
  #     Date.iso8601('20010203')          #=> #<Date: 2001-02-03 ...>
  #     Date.iso8601('2001-W05-6')        #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self.iso8601: (String str, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.jd([jd=0[, start=Date::ITALY]])  ->  date
  # -->
  # Creates a date object denoting the given chronological Julian day number.
  #
  #     Date.jd(2451944)          #=> #<Date: 2001-02-03 ...>
  #     Date.jd(2451945)          #=> #<Date: 2001-02-04 ...>
  #     Date.jd(0)                #=> #<Date: -4712-01-01 ...>
  #
  # See also ::new.
  #
  def self.jd: (Integer jd, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.jisx0301(string='-4712-01-01'[, start=Date::ITALY], limit: 128)  ->  date
  # -->
  # Creates a new Date object by parsing from a string according to some typical
  # JIS X 0301 formats.
  #
  #     Date.jisx0301('H13.02.03')                #=> #<Date: 2001-02-03 ...>
  #
  # For no-era year, legacy format, Heisei is assumed.
  #
  #     Date.jisx0301('13.02.03')                 #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self.jisx0301: (String str, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.julian_leap?(year)  ->  bool
  # -->
  # Returns true if the given year is a leap year of the proleptic Julian
  # calendar.
  #
  #     Date.julian_leap?(1900)           #=> true
  #     Date.julian_leap?(1901)           #=> false
  #
  def self.julian_leap?: (Integer year) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.gregorian_leap?(year)  ->  bool
  #   - Date.leap?(year)            ->  bool
  # -->
  # Returns true if the given year is a leap year of the proleptic Gregorian
  # calendar.
  #
  #     Date.gregorian_leap?(1900)        #=> false
  #     Date.gregorian_leap?(2000)        #=> true
  #
  def self.leap?: (Integer year) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.ordinal([year=-4712[, yday=1[, start=Date::ITALY]]])  ->  date
  # -->
  # Creates a date object denoting the given ordinal date.
  #
  # The day of year should be a negative or a positive number (as a relative day
  # from the end of year when negative).  It should not be zero.
  #
  #     Date.ordinal(2001)        #=> #<Date: 2001-01-01 ...>
  #     Date.ordinal(2001,34)     #=> #<Date: 2001-02-03 ...>
  #     Date.ordinal(2001,-1)     #=> #<Date: 2001-12-31 ...>
  #
  # See also ::jd and ::new.
  #
  def self.ordinal: (?Integer year, ?Integer yday, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.parse(string='-4712-01-01'[, comp=true[, start=Date::ITALY]], limit: 128)  ->  date
  # -->
  # Parses the given representation of date and time, and creates a date object.
  #
  # This method *does not* function as a validator.  If the input string does not
  # match valid formats strictly, you may get a cryptic result.  Should consider
  # to use `Date.strptime` instead of this method as possible.
  #
  # If the optional second argument is true and the detected year is in the range
  # "00" to "99", considers the year a 2-digit form and makes it full.
  #
  #     Date.parse('2001-02-03')          #=> #<Date: 2001-02-03 ...>
  #     Date.parse('20010203')            #=> #<Date: 2001-02-03 ...>
  #     Date.parse('3rd Feb 2001')        #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self.parse: (String str, ?boolish complete, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.rfc2822(string='Mon, 1 Jan -4712 00:00:00 +0000'[, start=Date::ITALY], limit: 128)  ->  date
  #   - Date.rfc822(string='Mon, 1 Jan -4712 00:00:00 +0000'[, start=Date::ITALY], limit: 128)   ->  date
  # -->
  # Creates a new Date object by parsing from a string according to some typical
  # RFC 2822 formats.
  #
  #     Date.rfc2822('Sat, 3 Feb 2001 00:00:00 +0000')
  #                                               #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self.rfc2822: (String str, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.rfc3339(string='-4712-01-01T00:00:00+00:00'[, start=Date::ITALY], limit: 128)  ->  date
  # -->
  # Creates a new Date object by parsing from a string according to some typical
  # RFC 3339 formats.
  #
  #     Date.rfc3339('2001-02-03T04:05:06+07:00') #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self.rfc3339: (String str, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.rfc2822(string='Mon, 1 Jan -4712 00:00:00 +0000'[, start=Date::ITALY], limit: 128)  ->  date
  #   - Date.rfc822(string='Mon, 1 Jan -4712 00:00:00 +0000'[, start=Date::ITALY], limit: 128)   ->  date
  # -->
  # Creates a new Date object by parsing from a string according to some typical
  # RFC 2822 formats.
  #
  #     Date.rfc2822('Sat, 3 Feb 2001 00:00:00 +0000')
  #                                               #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self.rfc822: (String str, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.strptime([string='-4712-01-01'[, format='%F'[, start=Date::ITALY]]])  ->  date
  # -->
  # Parses the given representation of date and time with the given template, and
  # creates a date object.  strptime does not support specification of flags and
  # width unlike strftime.
  #
  #     Date.strptime('2001-02-03', '%Y-%m-%d')   #=> #<Date: 2001-02-03 ...>
  #     Date.strptime('03-02-2001', '%d-%m-%Y')   #=> #<Date: 2001-02-03 ...>
  #     Date.strptime('2001-034', '%Y-%j')        #=> #<Date: 2001-02-03 ...>
  #     Date.strptime('2001-W05-6', '%G-W%V-%u')  #=> #<Date: 2001-02-03 ...>
  #     Date.strptime('2001 04 6', '%Y %U %w')    #=> #<Date: 2001-02-03 ...>
  #     Date.strptime('2001 05 6', '%Y %W %u')    #=> #<Date: 2001-02-03 ...>
  #     Date.strptime('sat3feb01', '%a%d%b%y')    #=> #<Date: 2001-02-03 ...>
  #
  # See also strptime(3) and #strftime.
  #
  def self.strptime: (String str, ?String format, ?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.today([start=Date::ITALY])  ->  date
  # -->
  # Creates a date object denoting the present day.
  #
  #     Date.today   #=> #<Date: 2011-06-11 ...>
  #
  def self.today: (?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.valid_civil?(year, month, mday[, start=Date::ITALY])  ->  bool
  #   - Date.valid_date?(year, month, mday[, start=Date::ITALY])   ->  bool
  # -->
  # Returns true if the given calendar date is valid, and false if not. Valid in
  # this context is whether the arguments passed to this method would be accepted
  # by ::new.
  #
  #     Date.valid_date?(2001,2,3)        #=> true
  #     Date.valid_date?(2001,2,29)       #=> false
  #     Date.valid_date?(2001,2,-1)       #=> true
  #
  # See also ::jd and ::civil.
  #
  def self.valid_civil?: (Integer year, Integer month, Integer mday, ?Integer start) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.valid_commercial?(cwyear, cweek, cwday[, start=Date::ITALY])  ->  bool
  # -->
  # Returns true if the given week date is valid, and false if not.
  #
  #     Date.valid_commercial?(2001,5,6)  #=> true
  #     Date.valid_commercial?(2001,5,8)  #=> false
  #
  # See also ::jd and ::commercial.
  #
  def self.valid_commercial?: (Integer cwyear, Integer cweek, Integer cwday, ?Integer start) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.valid_civil?(year, month, mday[, start=Date::ITALY])  ->  bool
  #   - Date.valid_date?(year, month, mday[, start=Date::ITALY])   ->  bool
  # -->
  # Returns true if the given calendar date is valid, and false if not. Valid in
  # this context is whether the arguments passed to this method would be accepted
  # by ::new.
  #
  #     Date.valid_date?(2001,2,3)        #=> true
  #     Date.valid_date?(2001,2,29)       #=> false
  #     Date.valid_date?(2001,2,-1)       #=> true
  #
  # See also ::jd and ::civil.
  #
  def self.valid_date?: (Integer year, Integer month, Integer mday, ?Integer start) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.valid_jd?(jd[, start=Date::ITALY])  ->  bool
  # -->
  # Just returns true.  It's nonsense, but is for symmetry.
  #
  #     Date.valid_jd?(2451944)           #=> true
  #
  # See also ::jd.
  #
  def self.valid_jd?: (Integer jd, ?Integer start) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.valid_ordinal?(year, yday[, start=Date::ITALY])  ->  bool
  # -->
  # Returns true if the given ordinal date is valid, and false if not.
  #
  #     Date.valid_ordinal?(2001,34)      #=> true
  #     Date.valid_ordinal?(2001,366)     #=> false
  #
  # See also ::jd and ::ordinal.
  #
  def self.valid_ordinal?: (Integer year, Integer yday, ?Integer start) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - Date.xmlschema(string='-4712-01-01'[, start=Date::ITALY], limit: 128)  ->  date
  # -->
  # Creates a new Date object by parsing from a string according to some typical
  # XML Schema formats.
  #
  #     Date.xmlschema('2001-02-03')      #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def self.xmlschema: (String str, ?Integer start) -> Date

  public

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d + other  ->  date
  # -->
  # Returns a date object pointing `other` days after self.  The other should be a
  # numeric value.  If the other is a fractional number, assumes its precision is
  # at most nanosecond.
  #
  #     Date.new(2001,2,3) + 1    #=> #<Date: 2001-02-04 ...>
  #     DateTime.new(2001,2,3) + Rational(1,2)
  #                               #=> #<DateTime: 2001-02-03T12:00:00+00:00 ...>
  #     DateTime.new(2001,2,3) + Rational(-1,2)
  #                               #=> #<DateTime: 2001-02-02T12:00:00+00:00 ...>
  #     DateTime.jd(0,12) + DateTime.new(2001,2,3).ajd
  #                               #=> #<DateTime: 2001-02-03T00:00:00+00:00 ...>
  #
  def +: (Numeric & _ToR other) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d - other  ->  date or rational
  # -->
  # Returns the difference between the two dates if the other is a date object.
  # If the other is a numeric value, returns a date object pointing `other` days
  # before self.  If the other is a fractional number, assumes its precision is at
  # most nanosecond.
  #
  #     Date.new(2001,2,3) - 1   #=> #<Date: 2001-02-02 ...>
  #     DateTime.new(2001,2,3) - Rational(1,2)
  #                              #=> #<DateTime: 2001-02-02T12:00:00+00:00 ...>
  #     Date.new(2001,2,3) - Date.new(2001)
  #                              #=> (33/1)
  #     DateTime.new(2001,2,3) - DateTime.new(2001,2,2,12)
  #                              #=> (1/2)
  #
  def -: (Numeric & _ToR other) -> Date
       | (Date other) -> Rational

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d << n  ->  date
  # -->
  # Returns a date object pointing `n` months before self. The argument `n` should
  # be a numeric value.
  #
  #     Date.new(2001,2,3)  <<  1   #=> #<Date: 2001-01-03 ...>
  #     Date.new(2001,2,3)  << -2   #=> #<Date: 2001-04-03 ...>
  #
  # When the same day does not exist for the corresponding month, the last day of
  # the month is used instead:
  #
  #     Date.new(2001,3,28) << 1   #=> #<Date: 2001-02-28 ...>
  #     Date.new(2001,3,31) << 1   #=> #<Date: 2001-02-28 ...>
  #
  # This also results in the following, possibly unexpected, behavior:
  #
  #     Date.new(2001,3,31) << 2         #=> #<Date: 2001-01-31 ...>
  #     Date.new(2001,3,31) << 1 << 1    #=> #<Date: 2001-01-28 ...>
  #
  #     Date.new(2001,3,31) << 1 << -1   #=> #<Date: 2001-03-28 ...>
  #
  def <<: (Integer month) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d <=> other  -> -1, 0, +1 or nil
  # -->
  # Compares the two dates and returns -1, zero, 1 or nil.  The other should be a
  # date object or a numeric value as an astronomical Julian day number.
  #
  #     Date.new(2001,2,3) <=> Date.new(2001,2,4)   #=> -1
  #     Date.new(2001,2,3) <=> Date.new(2001,2,3)   #=> 0
  #     Date.new(2001,2,3) <=> Date.new(2001,2,2)   #=> 1
  #     Date.new(2001,2,3) <=> Object.new           #=> nil
  #     Date.new(2001,2,3) <=> Rational(4903887,2)  #=> 0
  #
  # See also Comparable.
  #
  def <=>: (untyped other) -> Integer?

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d === other  ->  bool
  # -->
  # Returns true if they are the same day.
  #
  #     Date.new(2001,2,3) === Date.new(2001,2,3)
  #                                       #=> true
  #     Date.new(2001,2,3) === Date.new(2001,2,4)
  #                                       #=> false
  #     DateTime.new(2001,2,3) === DateTime.new(2001,2,3,12)
  #                                       #=> true
  #     DateTime.new(2001,2,3) === DateTime.new(2001,2,3,0,0,0,'+24:00')
  #                                       #=> true
  #     DateTime.new(2001,2,3) === DateTime.new(2001,2,4,0,0,0,'+24:00')
  #                                       #=> false
  #
  def ===: (Date other) -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d >> n  ->  date
  # -->
  # Returns a date object pointing `n` months after self. The argument `n` should
  # be a numeric value.
  #
  #     Date.new(2001,2,3)  >>  1   #=> #<Date: 2001-03-03 ...>
  #     Date.new(2001,2,3)  >> -2   #=> #<Date: 2000-12-03 ...>
  #
  # When the same day does not exist for the corresponding month, the last day of
  # the month is used instead:
  #
  #     Date.new(2001,1,28) >> 1   #=> #<Date: 2001-02-28 ...>
  #     Date.new(2001,1,31) >> 1   #=> #<Date: 2001-02-28 ...>
  #
  # This also results in the following, possibly unexpected, behavior:
  #
  #     Date.new(2001,1,31) >> 2         #=> #<Date: 2001-03-31 ...>
  #     Date.new(2001,1,31) >> 1 >> 1    #=> #<Date: 2001-03-28 ...>
  #
  #     Date.new(2001,1,31) >> 1 >> -1   #=> #<Date: 2001-01-28 ...>
  #
  def >>: (Integer month) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.ajd  ->  rational
  # -->
  # Returns the astronomical Julian day number.  This is a fractional number,
  # which is not adjusted by the offset.
  #
  #     DateTime.new(2001,2,3,4,5,6,'+7').ajd     #=> (11769328217/4800)
  #     DateTime.new(2001,2,2,14,5,6,'-7').ajd    #=> (11769328217/4800)
  #
  def ajd: () -> Rational

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.amjd  ->  rational
  # -->
  # Returns the astronomical modified Julian day number.  This is a fractional
  # number, which is not adjusted by the offset.
  #
  #     DateTime.new(2001,2,3,4,5,6,'+7').amjd    #=> (249325817/4800)
  #     DateTime.new(2001,2,2,14,5,6,'-7').amjd   #=> (249325817/4800)
  #
  def amjd: () -> Rational

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.asctime  ->  string
  #   - d.ctime    ->  string
  # -->
  # Returns a string in asctime(3) format (but without "n\0" at the end).  This
  # method is equivalent to strftime('%c').
  #
  # See also asctime(3) or ctime(3).
  #
  def asctime: () -> String

  # <!-- rdoc-file=ext/date/date_core.c -->
  # Returns a string in asctime(3) format (but without "n\0" at the end).  This
  # method is equivalent to strftime('%c').
  #
  # See also asctime(3) or ctime(3).
  #
  def ctime: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.cwday  ->  fixnum
  # -->
  # Returns the day of calendar week (1-7, Monday is 1).
  #
  #     Date.new(2001,2,3).cwday          #=> 6
  #
  def cwday: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.cweek  ->  fixnum
  # -->
  # Returns the calendar week number (1-53).
  #
  #     Date.new(2001,2,3).cweek          #=> 5
  #
  def cweek: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.cwyear  ->  integer
  # -->
  # Returns the calendar week based year.
  #
  #     Date.new(2001,2,3).cwyear         #=> 2001
  #     Date.new(2000,1,1).cwyear         #=> 1999
  #
  def cwyear: () -> Integer

  # <!-- rdoc-file=ext/date/date_core.c -->
  # Returns the day of the month (1-31).
  #
  #     Date.new(2001,2,3).mday           #=> 3
  #
  def day: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.downto(min)              ->  enumerator
  #   - d.downto(min){|date| ...}  ->  self
  # -->
  # This method is equivalent to step(min, -1){|date| ...}.
  #
  def downto: (Date min) { (Date) -> untyped } -> Date
            | (Date min) -> Enumerator[Date, Date]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.england  ->  date
  # -->
  # This method is equivalent to new_start(Date::ENGLAND).
  #
  def england: () -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.friday?  ->  bool
  # -->
  # Returns true if the date is Friday.
  #
  def friday?: () -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.gregorian  ->  date
  # -->
  # This method is equivalent to new_start(Date::GREGORIAN).
  #
  def gregorian: () -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.gregorian?  ->  bool
  # -->
  # Returns true if the date is on or after the day of calendar reform.
  #
  #     Date.new(1582,10,15).gregorian?          #=> true
  #     (Date.new(1582,10,15) - 1).gregorian?    #=> false
  #
  def gregorian?: () -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.httpdate  ->  string
  # -->
  # This method is equivalent to strftime('%a, %d %b %Y %T GMT'). See also RFC
  # 2616.
  #
  def httpdate: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.inspect  ->  string
  # -->
  # Returns the value as a string for inspection.
  #
  #     Date.new(2001,2,3).inspect
  #               #=> "#<Date: 2001-02-03>"
  #     DateTime.new(2001,2,3,4,5,6,'-7').inspect
  #               #=> "#<DateTime: 2001-02-03T04:05:06-07:00>"
  #
  def inspect: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.iso8601    ->  string
  #   - d.xmlschema  ->  string
  # -->
  # This method is equivalent to strftime('%F').
  #
  def iso8601: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.italy  ->  date
  # -->
  # This method is equivalent to new_start(Date::ITALY).
  #
  def italy: () -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.jd  ->  integer
  # -->
  # Returns the Julian day number.  This is a whole number, which is adjusted by
  # the offset as the local time.
  #
  #     DateTime.new(2001,2,3,4,5,6,'+7').jd      #=> 2451944
  #     DateTime.new(2001,2,3,4,5,6,'-7').jd      #=> 2451944
  #
  def jd: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.jisx0301  ->  string
  # -->
  # Returns a string in a JIS X 0301 format.
  #
  #     Date.new(2001,2,3).jisx0301       #=> "H13.02.03"
  #
  def jisx0301: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.julian  ->  date
  # -->
  # This method is equivalent to new_start(Date::JULIAN).
  #
  def julian: () -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.julian?  ->  bool
  # -->
  # Returns true if the date is before the day of calendar reform.
  #
  #     Date.new(1582,10,15).julian?             #=> false
  #     (Date.new(1582,10,15) - 1).julian?       #=> true
  #
  def julian?: () -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.ld  ->  integer
  # -->
  # Returns the Lilian day number.  This is a whole number, which is adjusted by
  # the offset as the local time.
  #
  #     Date.new(2001,2,3).ld            #=> 152784
  #
  def ld: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.leap?  ->  bool
  # -->
  # Returns true if the year is a leap year.
  #
  #     Date.new(2000).leap?      #=> true
  #     Date.new(2001).leap?      #=> false
  #
  def leap?: () -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.mday  ->  fixnum
  #   - d.day   ->  fixnum
  # -->
  # Returns the day of the month (1-31).
  #
  #     Date.new(2001,2,3).mday           #=> 3
  #
  def mday: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.mjd  ->  integer
  # -->
  # Returns the modified Julian day number.  This is a whole number, which is
  # adjusted by the offset as the local time.
  #
  #     DateTime.new(2001,2,3,4,5,6,'+7').mjd     #=> 51943
  #     DateTime.new(2001,2,3,4,5,6,'-7').mjd     #=> 51943
  #
  def mjd: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.mon    ->  fixnum
  #   - d.month  ->  fixnum
  # -->
  # Returns the month (1-12).
  #
  #     Date.new(2001,2,3).mon            #=> 2
  #
  def mon: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.monday?  ->  bool
  # -->
  # Returns true if the date is Monday.
  #
  def monday?: () -> bool

  # <!-- rdoc-file=ext/date/date_core.c -->
  # Returns the month (1-12).
  #
  #     Date.new(2001,2,3).mon            #=> 2
  #
  def month: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.new_start([start=Date::ITALY])  ->  date
  # -->
  # Duplicates self and resets its day of calendar reform.
  #
  #     d = Date.new(1582,10,15)
  #     d.new_start(Date::JULIAN)         #=> #<Date: 1582-10-05 ...>
  #
  def new_start: (?Integer start) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.succ  ->  date
  #   - d.next  ->  date
  # -->
  # Returns a date object denoting the following day.
  #
  def next: () -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.next_day([n=1])  ->  date
  # -->
  # This method is equivalent to d + n.
  #
  def next_day: (?Integer day) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.next_month([n=1])  ->  date
  # -->
  # This method is equivalent to d >> n.
  #
  # See Date#>> for examples.
  #
  def next_month: (?Integer month) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.next_year([n=1])  ->  date
  # -->
  # This method is equivalent to d >> (n * 12).
  #
  #     Date.new(2001,2,3).next_year      #=> #<Date: 2002-02-03 ...>
  #     Date.new(2008,2,29).next_year     #=> #<Date: 2009-02-28 ...>
  #     Date.new(2008,2,29).next_year(4)  #=> #<Date: 2012-02-29 ...>
  #
  # See also Date#>>.
  #
  def next_year: (?Integer year) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.prev_day([n=1])  ->  date
  # -->
  # This method is equivalent to d - n.
  #
  def prev_day: (?Integer day) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.prev_month([n=1])  ->  date
  # -->
  # This method is equivalent to d << n.
  #
  # See Date#<< for examples.
  #
  def prev_month: (?Integer month) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.prev_year([n=1])  ->  date
  # -->
  # This method is equivalent to d << (n * 12).
  #
  #     Date.new(2001,2,3).prev_year      #=> #<Date: 2000-02-03 ...>
  #     Date.new(2008,2,29).prev_year     #=> #<Date: 2007-02-28 ...>
  #     Date.new(2008,2,29).prev_year(4)  #=> #<Date: 2004-02-29 ...>
  #
  # See also Date#<<.
  #
  def prev_year: (?Integer year) -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.rfc2822  ->  string
  #   - d.rfc822   ->  string
  # -->
  # This method is equivalent to strftime('%a, %-d %b %Y %T %z').
  #
  def rfc2822: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.rfc3339  ->  string
  # -->
  # This method is equivalent to strftime('%FT%T%:z').
  #
  def rfc3339: () -> String

  # <!-- rdoc-file=ext/date/date_core.c -->
  # Creates a new Date object by parsing from a string according to some typical
  # RFC 2822 formats.
  #
  #     Date.rfc2822('Sat, 3 Feb 2001 00:00:00 +0000')
  #                                               #=> #<Date: 2001-02-03 ...>
  #
  # Raise an ArgumentError when the string length is longer than *limit*. You can
  # stop this check by passing `limit: nil`, but note that it may take a long time
  # to parse.
  #
  def rfc822: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.saturday?  ->  bool
  # -->
  # Returns true if the date is Saturday.
  #
  def saturday?: () -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.start  ->  float
  # -->
  # Returns the Julian day number denoting the day of calendar reform.
  #
  #     Date.new(2001,2,3).start                  #=> 2299161.0
  #     Date.new(2001,2,3,Date::GREGORIAN).start  #=> -Infinity
  #
  def start: () -> Float

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.step(limit[, step=1])              ->  enumerator
  #   - d.step(limit[, step=1]){|date| ...}  ->  self
  # -->
  # Iterates evaluation of the given block, which takes a date object. The limit
  # should be a date object.
  #
  #     Date.new(2001).step(Date.new(2001,-1,-1)).select{|d| d.sunday?}.size
  #                               #=> 52
  #
  def step: (Date limit, ?Integer step) { (Date) -> untyped } -> Date
          | (Date limit, ?Integer step) -> ::Enumerator[Date, Date]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.strftime([format='%F'])  ->  string
  # -->
  # Formats date according to the directives in the given format string. The
  # directives begin with a percent (%) character. Any text not listed as a
  # directive will be passed through to the output string.
  #
  # A directive consists of a percent (%) character, zero or more flags, an
  # optional minimum field width, an optional modifier, and a conversion specifier
  # as follows.
  #
  #     %<flags><width><modifier><conversion>
  #
  # Flags:
  #     -  don't pad a numerical output.
  #     _  use spaces for padding.
  #     0  use zeros for padding.
  #     ^  upcase the result string.
  #     #  change case.
  #
  # The minimum field width specifies the minimum width.
  #
  # The modifiers are "E", "O", ":", "::" and ":::". "E" and "O" are ignored.  No
  # effect to result currently.
  #
  # Format directives:
  #
  #     Date (Year, Month, Day):
  #       %Y - Year with century (can be negative, 4 digits at least)
  #               -0001, 0000, 1995, 2009, 14292, etc.
  #       %C - year / 100 (round down.  20 in 2009)
  #       %y - year % 100 (00..99)
  #
  #       %m - Month of the year, zero-padded (01..12)
  #               %_m  blank-padded ( 1..12)
  #               %-m  no-padded (1..12)
  #       %B - The full month name (``January'')
  #               %^B  uppercased (``JANUARY'')
  #       %b - The abbreviated month name (``Jan'')
  #               %^b  uppercased (``JAN'')
  #       %h - Equivalent to %b
  #
  #       %d - Day of the month, zero-padded (01..31)
  #               %-d  no-padded (1..31)
  #       %e - Day of the month, blank-padded ( 1..31)
  #
  #       %j - Day of the year (001..366)
  #
  #     Time (Hour, Minute, Second, Subsecond):
  #       %H - Hour of the day, 24-hour clock, zero-padded (00..23)
  #       %k - Hour of the day, 24-hour clock, blank-padded ( 0..23)
  #       %I - Hour of the day, 12-hour clock, zero-padded (01..12)
  #       %l - Hour of the day, 12-hour clock, blank-padded ( 1..12)
  #       %P - Meridian indicator, lowercase (``am'' or ``pm'')
  #       %p - Meridian indicator, uppercase (``AM'' or ``PM'')
  #
  #       %M - Minute of the hour (00..59)
  #
  #       %S - Second of the minute (00..60)
  #
  #       %L - Millisecond of the second (000..999)
  #       %N - Fractional seconds digits, default is 9 digits (nanosecond)
  #               %3N  millisecond (3 digits)   %15N femtosecond (15 digits)
  #               %6N  microsecond (6 digits)   %18N attosecond  (18 digits)
  #               %9N  nanosecond  (9 digits)   %21N zeptosecond (21 digits)
  #               %12N picosecond (12 digits)   %24N yoctosecond (24 digits)
  #
  #     Time zone:
  #       %z - Time zone as hour and minute offset from UTC (e.g. +0900)
  #               %:z - hour and minute offset from UTC with a colon (e.g. +09:00)
  #               %::z - hour, minute and second offset from UTC (e.g. +09:00:00)
  #               %:::z - hour, minute and second offset from UTC
  #                                                 (e.g. +09, +09:30, +09:30:30)
  #       %Z - Equivalent to %:z (e.g. +09:00)
  #
  #     Weekday:
  #       %A - The full weekday name (``Sunday'')
  #               %^A  uppercased (``SUNDAY'')
  #       %a - The abbreviated name (``Sun'')
  #               %^a  uppercased (``SUN'')
  #       %u - Day of the week (Monday is 1, 1..7)
  #       %w - Day of the week (Sunday is 0, 0..6)
  #
  #     ISO 8601 week-based year and week number:
  #     The week 1 of YYYY starts with a Monday and includes YYYY-01-04.
  #     The days in the year before the first week are in the last week of
  #     the previous year.
  #       %G - The week-based year
  #       %g - The last 2 digits of the week-based year (00..99)
  #       %V - Week number of the week-based year (01..53)
  #
  #     Week number:
  #     The week 1 of YYYY starts with a Sunday or Monday (according to %U
  #     or %W).  The days in the year before the first week are in week 0.
  #       %U - Week number of the year.  The week starts with Sunday.  (00..53)
  #       %W - Week number of the year.  The week starts with Monday.  (00..53)
  #
  #     Seconds since the Unix Epoch:
  #       %s - Number of seconds since 1970-01-01 00:00:00 UTC.
  #       %Q - Number of milliseconds since 1970-01-01 00:00:00 UTC.
  #
  #     Literal string:
  #       %n - Newline character (\n)
  #       %t - Tab character (\t)
  #       %% - Literal ``%'' character
  #
  #     Combination:
  #       %c - date and time (%a %b %e %T %Y)
  #       %D - Date (%m/%d/%y)
  #       %F - The ISO 8601 date format (%Y-%m-%d)
  #       %v - VMS date (%e-%^b-%Y)
  #       %x - Same as %D
  #       %X - Same as %T
  #       %r - 12-hour time (%I:%M:%S %p)
  #       %R - 24-hour time (%H:%M)
  #       %T - 24-hour time (%H:%M:%S)
  #       %+ - date(1) (%a %b %e %H:%M:%S %Z %Y)
  #
  # This method is similar to the strftime() function defined in ISO C and POSIX.
  # Several directives (%a, %A, %b, %B, %c, %p, %r, %x, %X, %E*, %O* and %Z) are
  # locale dependent in the function. However, this method is locale independent.
  # So, the result may differ even if the same format string is used in other
  # systems such as C. It is good practice to avoid %x and %X because there are
  # corresponding locale independent representations, %D and %T.
  #
  # Examples:
  #
  #     d = DateTime.new(2007,11,19,8,37,48,"-06:00")
  #                               #=> #<DateTime: 2007-11-19T08:37:48-0600 ...>
  #     d.strftime("Printed on %m/%d/%Y")   #=> "Printed on 11/19/2007"
  #     d.strftime("at %I:%M%p")            #=> "at 08:37AM"
  #
  # Various ISO 8601 formats:
  #     %Y%m%d           => 20071119                  Calendar date (basic)
  #     %F               => 2007-11-19                Calendar date (extended)
  #     %Y-%m            => 2007-11                   Calendar date, reduced accuracy, specific month
  #     %Y               => 2007                      Calendar date, reduced accuracy, specific year
  #     %C               => 20                        Calendar date, reduced accuracy, specific century
  #     %Y%j             => 2007323                   Ordinal date (basic)
  #     %Y-%j            => 2007-323                  Ordinal date (extended)
  #     %GW%V%u          => 2007W471                  Week date (basic)
  #     %G-W%V-%u        => 2007-W47-1                Week date (extended)
  #     %GW%V            => 2007W47                   Week date, reduced accuracy, specific week (basic)
  #     %G-W%V           => 2007-W47                  Week date, reduced accuracy, specific week (extended)
  #     %H%M%S           => 083748                    Local time (basic)
  #     %T               => 08:37:48                  Local time (extended)
  #     %H%M             => 0837                      Local time, reduced accuracy, specific minute (basic)
  #     %H:%M            => 08:37                     Local time, reduced accuracy, specific minute (extended)
  #     %H               => 08                        Local time, reduced accuracy, specific hour
  #     %H%M%S,%L        => 083748,000                Local time with decimal fraction, comma as decimal sign (basic)
  #     %T,%L            => 08:37:48,000              Local time with decimal fraction, comma as decimal sign (extended)
  #     %H%M%S.%L        => 083748.000                Local time with decimal fraction, full stop as decimal sign (basic)
  #     %T.%L            => 08:37:48.000              Local time with decimal fraction, full stop as decimal sign (extended)
  #     %H%M%S%z         => 083748-0600               Local time and the difference from UTC (basic)
  #     %T%:z            => 08:37:48-06:00            Local time and the difference from UTC (extended)
  #     %Y%m%dT%H%M%S%z  => 20071119T083748-0600      Date and time of day for calendar date (basic)
  #     %FT%T%:z         => 2007-11-19T08:37:48-06:00 Date and time of day for calendar date (extended)
  #     %Y%jT%H%M%S%z    => 2007323T083748-0600       Date and time of day for ordinal date (basic)
  #     %Y-%jT%T%:z      => 2007-323T08:37:48-06:00   Date and time of day for ordinal date (extended)
  #     %GW%V%uT%H%M%S%z => 2007W471T083748-0600      Date and time of day for week date (basic)
  #     %G-W%V-%uT%T%:z  => 2007-W47-1T08:37:48-06:00 Date and time of day for week date (extended)
  #     %Y%m%dT%H%M      => 20071119T0837             Calendar date and local time (basic)
  #     %FT%R            => 2007-11-19T08:37          Calendar date and local time (extended)
  #     %Y%jT%H%MZ       => 2007323T0837Z             Ordinal date and UTC of day (basic)
  #     %Y-%jT%RZ        => 2007-323T08:37Z           Ordinal date and UTC of day (extended)
  #     %GW%V%uT%H%M%z   => 2007W471T0837-0600        Week date and local time and difference from UTC (basic)
  #     %G-W%V-%uT%R%:z  => 2007-W47-1T08:37-06:00    Week date and local time and difference from UTC (extended)
  #
  # See also strftime(3) and ::strptime.
  #
  def strftime: (?String format) -> String

  # <!-- rdoc-file=ext/date/date_core.c -->
  # Returns a date object denoting the following day.
  #
  def succ: () -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.sunday?  ->  bool
  # -->
  # Returns true if the date is Sunday.
  #
  def sunday?: () -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.thursday?  ->  bool
  # -->
  # Returns true if the date is Thursday.
  #
  def thursday?: () -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.to_date  ->  self
  # -->
  # Returns self.
  #
  def to_date: () -> Date

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.to_datetime  -> datetime
  # -->
  # Returns a DateTime object which denotes self.
  #
  def to_datetime: () -> DateTime

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.to_s  ->  string
  # -->
  # Returns a string in an ISO 8601 format. (This method doesn't use the expanded
  # representations.)
  #
  #     Date.new(2001,2,3).to_s  #=> "2001-02-03"
  #
  def to_s: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.to_time  ->  time
  # -->
  # Returns a Time object which denotes self. If self is a julian date, convert it
  # to a gregorian date before converting it to Time.
  #
  def to_time: () -> Time

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.tuesday?  ->  bool
  # -->
  # Returns true if the date is Tuesday.
  #
  def tuesday?: () -> bool

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.upto(max)              ->  enumerator
  #   - d.upto(max){|date| ...}  ->  self
  # -->
  # This method is equivalent to step(max, 1){|date| ...}.
  #
  def upto: (Date max) { (Date) -> untyped } -> Date
          | (Date max) -> ::Enumerator[Date, Date]

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.wday  ->  fixnum
  # -->
  # Returns the day of week (0-6, Sunday is zero).
  #
  #     Date.new(2001,2,3).wday           #=> 6
  #
  def wday: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.wednesday?  ->  bool
  # -->
  # Returns true if the date is Wednesday.
  #
  def wednesday?: () -> bool

  # <!-- rdoc-file=ext/date/date_core.c -->
  # This method is equivalent to strftime('%F').
  #
  def xmlschema: () -> String

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.yday  ->  fixnum
  # -->
  # Returns the day of the year (1-366).
  #
  #     Date.new(2001,2,3).yday           #=> 34
  #
  def yday: () -> Integer

  # <!--
  #   rdoc-file=ext/date/date_core.c
  #   - d.year  ->  integer
  # -->
  # Returns the year.
  #
  #     Date.new(2001,2,3).year           #=> 2001
  #     (Date.new(1,1,1) - 1).year        #=> 0
  #
  def year: () -> Integer
end

# <!-- rdoc-file=ext/date/date_core.c -->
# An array of strings of abbreviated day names in English.  The first is "Sun".
#
Date::ABBR_DAYNAMES: Array[String]

# <!-- rdoc-file=ext/date/date_core.c -->
# An array of strings of abbreviated month names in English.  The first element
# is nil.
#
Date::ABBR_MONTHNAMES: Array[String?]

# <!-- rdoc-file=ext/date/date_core.c -->
# An array of strings of the full names of days of the week in English. The
# first is "Sunday".
#
Date::DAYNAMES: Array[String]

# <!-- rdoc-file=ext/date/date_core.c -->
# The Julian day number of the day of calendar reform for England and her
# colonies.
#
Date::ENGLAND: Integer

# <!-- rdoc-file=ext/date/date_core.c -->
# The Julian day number of the day of calendar reform for the proleptic
# Gregorian calendar.
#
Date::GREGORIAN: Integer

# <!-- rdoc-file=ext/date/date_core.c -->
# The Julian day number of the day of calendar reform for Italy and some
# catholic countries.
#
Date::ITALY: Integer

# <!-- rdoc-file=ext/date/date_core.c -->
# The Julian day number of the day of calendar reform for the proleptic Julian
# calendar.
#
Date::JULIAN: Integer

# <!-- rdoc-file=ext/date/date_core.c -->
# An array of strings of full month names in English.  The first element is nil.
#
Date::MONTHNAMES: Array[String?]
