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ext/date/date_core.c: [DOC] fold long paragraphs
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@ -9477,7 +9477,16 @@ Init_date_core(void)
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### When should you use DateTime and when should you use Time?
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### When should you use DateTime and when should you use Time?
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It's a common misconception that [William Shakespeare][1] and [Miguel de Cervantes][2] died on the same day in history - so much so that UNESCO named April 23 as [World Book Day because of this fact][3]. However because England hadn't yet adopted [Gregorian Calendar Reform][4] (and wouldn't until [1752][5]) their deaths are actually 10 days apart. Since Ruby's `Time` class implements a [proleptic Gregorian calendar][6] and has no concept of calendar reform then there's no way to express this. This is where `DateTime` steps in:
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It's a common misconception that [William Shakespeare][1] and
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[Miguel de Cervantes][2] died on the same day in history -
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so much so that UNESCO named April 23 as [World Book Day
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because of this fact][3].
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However because England hadn't yet adopted [Gregorian Calendar
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Reform][4] (and wouldn't until [1752][5]) their deaths are
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actually 10 days apart. Since Ruby's `Time` class implements a
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[proleptic Gregorian calendar][6] and has no concept of
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calendar reform then there's no way to express this. This is
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where `DateTime` steps in:
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``` irb
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``` irb
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>> shakespeare = DateTime.iso8601('1616-04-23', Date::ENGLAND)
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>> shakespeare = DateTime.iso8601('1616-04-23', Date::ENGLAND)
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@ -9486,7 +9495,8 @@ Init_date_core(void)
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=> Sat, 23 Apr 1616 00:00:00 +0000
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=> Sat, 23 Apr 1616 00:00:00 +0000
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```
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```
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Already you can see something's weird - the days of the week are different, taking this further:
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Already you can see something's weird - the days of the week
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are different, taking this further:
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``` irb
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``` irb
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>> cervantes == shakespeare
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>> cervantes == shakespeare
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@ -9495,14 +9505,21 @@ Init_date_core(void)
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=> 10
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=> 10
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```
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```
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This shows that in fact they died 10 days apart (in reality 11 days since Cervantes died a day earlier but was buried on the 23rd). We can see the actual date of Shakespeare's death by using the `gregorian` method to convert it:
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This shows that in fact they died 10 days apart (in reality 11
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days since Cervantes died a day earlier but was buried on the
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23rd). We can see the actual date of Shakespeare's death by
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using the `gregorian` method to convert it:
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``` irb
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``` irb
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>> shakespeare.gregorian
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>> shakespeare.gregorian
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=> Tue, 03 May 1616 00:00:00 +0000
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=> Tue, 03 May 1616 00:00:00 +0000
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```
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```
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So there's an argument that all the celebrations that take place on the 23rd April in Stratford-upon-Avon are actually the wrong date since England is now using the Gregorian calendar. You can see why when we transition across the reform date boundary:
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So there's an argument that all the celebrations that take
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place on the 23rd April in Stratford-upon-Avon are actually
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the wrong date since England is now using the Gregorian
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calendar. You can see why when we transition across the reform
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date boundary:
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``` irb
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``` irb
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# start off with the anniversary of Shakespeare's birth in 1751
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# start off with the anniversary of Shakespeare's birth in 1751
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@ -9518,9 +9535,21 @@ Init_date_core(void)
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=> Fri, 04 May 1753 00:00:00 +0000
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=> Fri, 04 May 1753 00:00:00 +0000
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```
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```
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As you can see, if we're accurately tracking the number of [solar years][9] since Shakespeare's birthday then the correct anniversary date would be the 4th May and not the 23rd April.
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As you can see, if we're accurately tracking the number of
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[solar years][9] since Shakespeare's birthday then the correct
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anniversary date would be the 4th May and not the 23rd April.
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So when should use you use `DateTime` in Ruby and when should you use `Time`? Almost certainly you'll want to use `Time` since your app is probably dealing with current dates and times. However, if you need to deal with dates and times in a historical context you'll want to use `DateTime` to avoid making the same mistakes as UNESCO. If you also have to deal with timezones then best of luck - just bear in mind that you'll probably be dealing with [local solar times][7], since it wasn't until the 19th century that the introduction of the railways necessitated the need for [Standard Time][8] and eventually timezones.
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So when should use you use `DateTime` in Ruby and when should
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you use `Time`? Almost certainly you'll want to use `Time`
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since your app is probably dealing with current dates and
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times. However, if you need to deal with dates and times in a
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historical context you'll want to use `DateTime` to avoid
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making the same mistakes as UNESCO. If you also have to deal
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with timezones then best of luck - just bear in mind that
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you'll probably be dealing with [local solar times][7], since
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it wasn't until the 19th century that the introduction of the
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railways necessitated the need for [Standard Time][8] and
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eventually timezones.
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[1]: http://en.wikipedia.org/wiki/William_Shakespeare
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[1]: http://en.wikipedia.org/wiki/William_Shakespeare
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[2]: http://en.wikipedia.org/wiki/Miguel_de_Cervantes
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[2]: http://en.wikipedia.org/wiki/Miguel_de_Cervantes
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