Time

A Time object represents a date and time:

Time.new(2000, 1, 1, 0, 0, 0) # => 2000-01-01 00:00:00 -0600

Although its value can be expressed as a single numeric (see Epoch Seconds below), it can be convenient to deal with the value by parts:

t = Time.new(-2000, 1, 1, 0, 0, 0.0)
# => -2000-01-01 00:00:00 -0600
t.year # => -2000
t.month # => 1
t.mday # => 1
t.hour # => 0
t.min # => 0
t.sec # => 0
t.subsec # => 0

t = Time.new(2000, 12, 31, 23, 59, 59.5)
# => 2000-12-31 23:59:59.5 -0600
t.year # => 2000
t.month # => 12
t.mday # => 31
t.hour # => 23
t.min # => 59
t.sec # => 59
t.subsec # => (1/2)

Epoch Seconds

Epoch seconds is the exact number of seconds (including fractional subseconds) since the Unix Epoch, January 1, 1970.

You can retrieve that value exactly using method Time.to_r:

Time.at(0).to_r        # => (0/1)
Time.at(0.999999).to_r # => (9007190247541737/9007199254740992)

Other retrieval methods such as Time#to_i and Time#to_f may return a value that rounds or truncates subseconds.

Time Resolution

A Time object derived from the system clock (for example, by method Time.now) has the resolution supported by the system.

Time Internal Representation

Conceptually, Time class uses a rational value to represent the number of seconds from Epoch, 1970-01-01 00:00:00 UTC. There are no boundary or resolution limitations. The value can be obtained using Time#to_r.

The Time class always uses the Gregorian calendar. I.e. the proleptic Gregorian calendar is used. Other calendars, such as Julian calendar, are not supported.

The implementation uses a signed 63 bit integer, Integer (Bignum) object or Ratoinal object to represent a rational value. (The signed 63 bit integer is used regardless of 32 and 64 bit environments.) The value represents the number of nanoseconds from Epoch. The signed 63 bit integer can represent 1823-11-12 to 2116-02-20. When Integer or Rational object is used (before 1823, after 2116, under nanosecond), Time works slower than when the signed 63 bit integer is used.

Ruby uses the C function localtime and gmtime to map between the number and 6-tuple (year,month,day,hour,minute,second). localtime is used for local time and gmtime is used for UTC.

Integer and Rational has no range limit, but the localtime and gmtime has range limits due to the C types time_t and struct tm. If that limit is exceeded, Ruby extrapolates the localtime function.

time_t can represent 1901-12-14 to 2038-01-19 if it is 32 bit signed integer, -292277022657-01-27 to 292277026596-12-05 if it is 64 bit signed integer. However localtime on some platforms doesn’t supports negative time_t (before 1970).

struct tm has tm_year member to represent years. (tm_year = 0 means the year 1900.) It is defined as int in the C standard. tm_year can represent years between -2147481748 to 2147485547 if int is 32 bit.

Ruby supports leap seconds as far as if the C function localtime and gmtime supports it. They use the tz database in most Unix systems. The tz database has timezones which supports leap seconds. For example, “Asia/Tokyo” doesn’t support leap seconds but “right/Asia/Tokyo” supports leap seconds. So, Ruby supports leap seconds if the TZ environment variable is set to “right/Asia/Tokyo” in most Unix systems.

Examples

All of these examples were done using the EST timezone which is GMT-5.

Creating a New Time Instance

You can create a new instance of Time with Time.new. This will use the current system time. Time.now is an alias for this. You can also pass parts of the time to Time.new such as year, month, minute, etc. When you want to construct a time this way you must pass at least a year. If you pass the year with nothing else time will default to January 1 of that year at 00:00:00 with the current system timezone. Here are some examples:

Time.new(2002)         #=> 2002-01-01 00:00:00 -0500
Time.new(2002, 10)     #=> 2002-10-01 00:00:00 -0500
Time.new(2002, 10, 31) #=> 2002-10-31 00:00:00 -0500

You can pass a UTC offset:

Time.new(2002, 10, 31, 2, 2, 2, "+02:00") #=> 2002-10-31 02:02:02 +0200

Or a timezone object:

zone = timezone("Europe/Athens")      # Eastern European Time, UTC+2
Time.new(2002, 10, 31, 2, 2, 2, zone) #=> 2002-10-31 02:02:02 +0200

You can also use Time.local and Time.utc to infer local and UTC timezones instead of using the current system setting.

You can also create a new time using Time.at which takes the number of seconds (with subsecond) since the Unix Epoch.

Time.at(628232400) #=> 1989-11-28 00:00:00 -0500

Working with an Instance of Time

Once you have an instance of Time there is a multitude of things you can do with it. Below are some examples. For all of the following examples, we will work on the assumption that you have done the following:

t = Time.new(1993, 02, 24, 12, 0, 0, "+09:00")

Was that a monday?

t.monday? #=> false

What year was that again?

t.year #=> 1993

Was it daylight savings at the time?

t.dst? #=> false

What’s the day a year later?

t + (60*60*24*365) #=> 1994-02-24 12:00:00 +0900

How many seconds was that since the Unix Epoch?

t.to_i #=> 730522800

You can also do standard functions like compare two times.

t1 = Time.new(2010)
t2 = Time.new(2011)

t1 == t2 #=> false
t1 == t1 #=> true
t1 <  t2 #=> true
t1 >  t2 #=> false

Time.new(2010,10,31).between?(t1, t2) #=> true

What’s Here

First, what’s elsewhere. Class Time:

• Inherits from class Object.

• Includes module Comparable.

Here, class Time provides methods that are useful for:

• Creating Time objects.

• Fetching Time values.

• Querying a Time object.

• Comparing Time objects.

• Converting a Time object.

• Rounding a Time.

Methods for Creating

• ::new: Returns a new time from specified arguments (year, month, etc.), including an optional timezone value.

• ::local (aliased as ::mktime): Same as ::new, except the timezone is the local timezone.

• ::utc (aliased as ::gm): Same as ::new, except the timezone is UTC.

• ::at: Returns a new time based on seconds since epoch.

• ::now: Returns a new time based on the current system time.

• + (plus): Returns a new time increased by the given number of seconds.

• - (minus): Returns a new time decreased by the given number of seconds.

Methods for Fetching

• year: Returns the year of the time.

• month (aliased as mon): Returns the month of the time.

• mday (aliased as day): Returns the day of the month.

• hour: Returns the hours value for the time.

• min: Returns the minutes value for the time.

• sec: Returns the seconds value for the time.

• usec (aliased as tv_usec): Returns the number of microseconds in the subseconds value of the time.

• nsec (aliased as tv_nsec: Returns the number of nanoseconds in the subsecond part of the time.

• subsec: Returns the subseconds value for the time.

• wday: Returns the integer weekday value of the time (0 == Sunday).

• yday: Returns the integer yearday value of the time (1 == January 1).

• hash: Returns the integer hash value for the time.

• utc_offset (aliased as gmt_offset and gmtoff): Returns the offset in seconds between time and UTC.

• to_f: Returns the float number of seconds since epoch for the time.

• to_i (aliased as tv_sec): Returns the integer number of seconds since epoch for the time.

• to_r: Returns the Rational number of seconds since epoch for the time.

• zone: Returns a string representation of the timezone of the time.

Methods for Querying

• utc? (aliased as gmt?): Returns whether the time is UTC.

• dst? (aliased as isdst): Returns whether the time is DST (daylight saving time).

• sunday?: Returns whether the time is a Sunday.

• monday?: Returns whether the time is a Monday.

• tuesday?: Returns whether the time is a Tuesday.

• wednesday?: Returns whether the time is a Wednesday.

• thursday?: Returns whether the time is a Thursday.

• friday?: Returns whether time is a Friday.

• saturday?: Returns whether the time is a Saturday.

Methods for Comparing

• <=>: Compares self to another time.

• eql?: Returns whether the time is equal to another time.

Methods for Converting

• asctime (aliased as ctime): Returns the time as a string.

• inspect: Returns the time in detail as a string.

• strftime: Returns the time as a string, according to a given format.

• to_a: Returns a 10-element array of values from the time.

• to_s: Returns a string representation of the time.

• getutc (aliased as getgm): Returns a new time converted to UTC.

• getlocal: Returns a new time converted to local time.

• utc (aliased as gmtime): Converts time to UTC in place.

• localtime: Converts time to local time in place.

• deconstruct_keys: Returns a hash of time components used in pattern-matching.

Methods for Rounding

• round:Returns a new time with subseconds rounded.

• ceil: Returns a new time with subseconds raised to a ceiling.

• floor: Returns a new time with subseconds lowered to a floor.

For the forms of argument zone, see Timezone Specifiers.

Timezone Specifiers

Certain Time methods accept arguments that specify timezones:

• Time.at: keyword argument in:.

• Time.new: positional argument zone or keyword argument in:.

• Time.now: keyword argument in:.

• Time#getlocal: positional argument zone.

• Time#localtime: positional argument zone.

The value given with any of these must be one of the following (each detailed below):

• Hours/minutes offset.

• Single-letter offset.

• Integer offset.

• Timezone object.

• Timezone name.

Hours/Minutes Offsets

The zone value may be a string offset from UTC in the form '+HH:MM' or '-HH:MM', where:

• HH is the 2-digit hour in the range 0..23.

• MM is the 2-digit minute in the range 0..59.

Examples:

t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
Time.at(t, in: '-23:59')            # => 1999-12-31 20:16:01 -2359
Time.at(t, in: '+23:59')            # => 2000-01-02 20:14:01 +2359

Single-Letter Offsets

The zone value may be a letter in the range 'A'..'I' or 'K'..'Z'; see List of military time zones:

t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
Time.at(t, in: 'A')                 # => 2000-01-01 21:15:01 +0100
Time.at(t, in: 'I')                 # => 2000-01-02 05:15:01 +0900
Time.at(t, in: 'K')                 # => 2000-01-02 06:15:01 +1000
Time.at(t, in: 'Y')                 # => 2000-01-01 08:15:01 -1200
Time.at(t, in: 'Z')                 # => 2000-01-01 20:15:01 UTC

Integer Offsets

The zone value may be an integer number of seconds in the range -86399..86399:

t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
Time.at(t, in: -86399)              # => 1999-12-31 20:15:02 -235959
Time.at(t, in: 86399)               # => 2000-01-02 20:15:00 +235959

Timezone Objects

The zone value may be an object responding to certain timezone methods, an instance of Timezone and TZInfo for example.

The timezone methods are:

• local_to_utc:

  Called when Time.new is invoked with tz as the value of positional argument zone or keyword argument in:.

  Argument

  a Time-like object.

  Returns

  a Time-like object in the UTC timezone.

• utc_to_local:

  Called when Time.at or Time.now is invoked with tz as the value for keyword argument in:, and when Time#getlocal or Time#localtime is called with tz as the value for positional argument zone.

  The UTC offset will be calculated as the difference between the original time and the returned object as an Integer. If the object is in fixed offset, its utc_offset is also counted.

  Argument

  a Time-like object.

  Returns

  a Time-like object in the local timezone.

A custom timezone class may have these instance methods, which will be called if defined:

• abbr:

  Called when Time#strftime is invoked with a format involving %Z.

  Argument

  a Time-like object.

  Returns

  a string abbreviation for the timezone name.

• dst?:

  Called when Time.at or Time.now is invoked with tz as the value for keyword argument in:, and when Time#getlocal or Time#localtime is called with tz as the value for positional argument zone.

  Argument

  a Time-like object.

  Returns

  whether the time is daylight saving time.

• name:

  Called when Marshal.dump(t) is invoked

  Argument

  none.

  Returns

  the string name of the timezone.

Time-Like Objects

A Time-like object is a container object capable of interfacing with timezone libraries for timezone conversion.

The argument to the timezone conversion methods above will have attributes similar to Time, except that timezone related attributes are meaningless.

The objects returned by local_to_utc and utc_to_local methods of the timezone object may be of the same class as their arguments, of arbitrary object classes, or of class Integer.

For a returned class other than Integer, the class must have the following methods:

• year

• mon

• mday

• hour

• min

• sec

• isdst

• to_i

For a returned Integer, its components, decomposed in UTC, are interpreted as times in the specified timezone.

Timezone Names

If the class (the receiver of class methods, or the class of the receiver of instance methods) has find_timezone singleton method, this method is called to achieve the corresponding timezone object from a timezone name.

For example, using Timezone:

class TimeWithTimezone < Time
  require 'timezone'
  def self.find_timezone(z) = Timezone[z]
end

TimeWithTimezone.now(in: "America/New_York")        #=> 2023-12-25 00:00:00 -0500
TimeWithTimezone.new("2023-12-25 America/New_York") #=> 2023-12-25 00:00:00 -0500

Or, using TZInfo:

class TimeWithTZInfo < Time
  require 'tzinfo'
  def self.find_timezone(z) = TZInfo::Timezone.get(z)
end

TimeWithTZInfo.now(in: "America/New_York")          #=> 2023-12-25 00:00:00 -0500
TimeWithTZInfo.new("2023-12-25 America/New_York")   #=> 2023-12-25 00:00:00 -0500

You can define this method per subclasses, or on the toplevel Time class.