Beginning of day given a Time value

ruby-talk
1

Anyone have a nice idiomatic way given an instance of Time, to return the
beginning of that day? Below is my approach but it just feels very wrong...

require "test/unit"
require "time"

class Time
  def begin_of_day
    Time.parse "#{self.month}/#{self.day}/#{self.year}"
  end
end

class TestBeginOfDay < Test::Unit::TestCase
  def test_begin_of_day
    start_of_day = Time.parse "10/1/2006 00:00"
    time = Time.parse "10/1/2006 9:45"
    assert_equal(start_of_day, time.begin_of_day)
  end
end

Thanks,
Michael Guterl

2

How about this?

class Time
    def begin_of_day
       self - 3600 * hour - 60 * min - sec
    end
end

It passes your unit test.

Regards, Morton

···

On Oct 9, 2006, at 9:45 AM, Michael Guterl wrote:

Anyone have a nice idiomatic way given an instance of Time, to return the
beginning of that day? Below is my approach but it just feels very wrong...

require "test/unit"
require "time"

class Time
def begin_of_day
   Time.parse "#{self.month}/#{self.day}/#{self.year}"
end
end

class TestBeginOfDay < Test::Unit::TestCase
def test_begin_of_day
   start_of_day = Time.parse "10/1/2006 00:00"
   time = Time.parse "10/1/2006 9:45"
   assert_equal(start_of_day, time.begin_of_day)
end
end

3

why are you using parse? without it your method is straightforward enough:

   harp:~ > cat a.rb
   require "test/unit"

   class Time
     def begining_of_day
       Time.mktime(year, month, day).send(gmt? ? :gmt : :localtime)
     end
   end

   class TestBeginOfDay < Test::Unit::TestCase
     def test_begin_of_day
       start_of_day = Time.mktime 2006, 10, 1
       time = Time.mktime 2006, 10, 1, 9, 45
       assert_equal start_of_day, time.begining_of_day
     end
   end

   harp:~ > ruby a.rb
   Loaded suite a
   Started
   .
   Finished in 0.000914 seconds.

   1 tests, 1 assertions, 0 failures, 0 errors

regards.

-a

···

On Mon, 9 Oct 2006, Michael Guterl wrote:

Anyone have a nice idiomatic way given an instance of Time, to return the
beginning of that day? Below is my approach but it just feels very wrong...

require "test/unit"
require "time"

class Time
def begin_of_day
  Time.parse "#{self.month}/#{self.day}/#{self.year}"
end

class TestBeginOfDay < Test::Unit::TestCase
def test_begin_of_day
  start_of_day = Time.parse "10/1/2006 00:00"
  time = Time.parse "10/1/2006 9:45"
  assert_equal(start_of_day, time.begin_of_day)
end

Thanks,
Michael Guterl

--
in order to be effective truth must penetrate like an arrow - and that is
likely to hurt. -- wei wu wei

4

How about this?

class Time
    def begin_of_day
       self - 3600 * hour - 60 * min - sec
    end
end

It passes your unit test.

ActiveSupport has a beginning_of_day method which is basically
equivalent to that

This approach fails will fail if daylight saving changes in between
midnight and the object on which you are calling begin_of_day. For
example in the UK on the 29th of october midday is 13 hours after the
previous midnight.

Fred

···

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