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108 lines
3.6 KiB
Text
108 lines
3.6 KiB
Text
== Timezones
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=== Timezone Specifiers
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Certain \Time methods accept arguments that specify timezones:
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- Time.at: keyword argument +in:+.
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- Time.new: positional argument +zone+ or keyword argument +in:+.
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- Time.now: keyword argument +in:+.
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- Time#getlocal: positional argument +zone+.
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- Time#localtime: positional argument +zone+.
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The value given with any of these must be one of the following
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(each detailed below):
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- {Hours/minutes offset}[rdoc-ref:timezones.rdoc@Hours-2FMinutes+Offsets].
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- {Single-letter offset}[rdoc-ref:timezones.rdoc@Single-Letter+Offsets].
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- {Integer offset}[rdoc-ref:timezones.rdoc@Integer+Offsets].
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- {Timezone object}[rdoc-ref:timezones.rdoc@Timezone+Objects].
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==== Hours/Minutes Offsets
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The zone value may be a string offset from UTC
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in the form <tt>'+HH:MM'</tt> or <tt>'-HH:MM'</tt>,
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where:
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- +HH+ is the 2-digit hour in the range <tt>0..23</tt>.
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- +MM+ is the 2-digit minute in the range <tt>0..59</tt>.
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Examples:
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t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
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Time.at(t, in: '-23:59') # => 1999-12-31 20:16:01 -2359
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Time.at(t, in: '+23:59') # => 2000-01-02 20:14:01 +2359
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==== Single-Letter Offsets
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The zone value may be a letter in the range <tt>'A'..'I'</tt>
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or <tt>'K'..'Z'</tt>;
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see {List of military time zones}[https://en.wikipedia.org/wiki/List_of_military_time_zones]:
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t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
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Time.at(t, in: 'A') # => 2000-01-01 21:15:01 +0100
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Time.at(t, in: 'I') # => 2000-01-02 05:15:01 +0900
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Time.at(t, in: 'K') # => 2000-01-02 06:15:01 +1000
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Time.at(t, in: 'Y') # => 2000-01-01 08:15:01 -1200
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Time.at(t, in: 'Z') # => 2000-01-01 20:15:01 UTC
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==== \Integer Offsets
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The zone value may be an integer number of seconds
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in the range <tt>-86399..86399</tt>:
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t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
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Time.at(t, in: -86399) # => 1999-12-31 20:15:02 -235959
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Time.at(t, in: 86399) # => 2000-01-02 20:15:00 +235959
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==== Timezone Objects
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In most cases, the zone value may be an object
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responding to certain timezone methods.
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\Exceptions (timezone object not allowed):
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- Time.new with positional argument +zone+.
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- Time.now with keyword argument +in:+.
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The timezone methods are:
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- +local_to_utc+:
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- Called when Time.new is invoked with +tz+
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as the value of positional argument +zone+ or keyword argument +in:+.
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- Argument: a <tt>Time::tm</tt> object.
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- Returns: a \Time-like object in the UTC timezone.
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- +utc_to_local+:
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- Called when Time.at or Time.now is invoked with +tz+
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as the value for keyword argument +in:+,
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and when Time#getlocal or Time#localtime is called with +tz+
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as the value for positional argument +zone+.
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- Argument: a <tt>Time::tm</tt> object.
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- Returns: a \Time-like object in the local timezone.
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A custom timezone class may have these instance methods,
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which will be called if defined:
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- +abbr+:
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- Called when Time#strftime is invoked with a format involving <tt>%Z</tt>.
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- Argument: a <tt>Time::tm</tt> object.
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- Returns: a string abbreviation for the timezone name.
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- +dst?+:
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- Called when Time.at or Time.now is invoked with +tz+
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as the value for keyword argument +in:+,
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and when Time#getlocal or Time#localtime is called with +tz+
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as the value for positional argument +zone+.
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- Argument: a <tt>Time::tm</tt> object.
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- Returns: whether the time is daylight saving time.
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- +name+:
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- Called when <tt>Marshal.dump(t) is invoked
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- Argument: none.
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- Returns: the string name of the timezone.
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