A Tale about Time - PHP.gent

Timezones, DST, human readable diffs, standardised formats, intervals, getting the last Tuesday of next month… Dealing with timestamps seems easy, but there’s a lot to it. It’s very easy to do it wrong. Learn how to do this properly and you’ll never be chasing weird time related bugs anymore!

Transcript

1. A Tale about Time
   @hannesvdvreken
   @phpgent
   

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2. Hi, my name is Hannes.
   

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3. !
   

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6. A Tale about Time
   

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7. 2018-09-18T19:00:00+02:00
   

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13. EDT = UTC-04:00
    CEST = UTC+02:00
    

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16. EDT = UTC-04:00
    CEST = UTC+02:00
    

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17. '
    UTC+05:30
    

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18. UTC+05:45
    

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19. DST
    CET/CEST
    

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20. Helsinki
    Sunrise: 9:24 - 3:54
    Sunset: 15:13 - 22:50
    Quito
    Sunrise: 6:08 - 6:12
    Sunset: 18:16 - 18:19
    

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23. EST/EDT - March 12
    CET/CEST - March 24
    

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24. (
    

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25. )/*
    

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26. Calendars
    

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27. Weeks - 7 days
    Starts on Monday. Or Sunday?
    First week of the year?
    

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28. Months
    Lunar vs Tropical
    

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29. Years
    Lunisolar vs Tropical
    

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30. 2018AD
    1500BC
    

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31. Leap years
    

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32. Leap years
    Leap seconds
    

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33. Storing vs Expressing time
    

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34. Expressing time:
    6:00PM vs 18:00
    

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35. Expressing time:
    September 18
    09/18/2018
    18/09/2018
    

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36. Storing time:
    1521261900 ($dt->timestamp)
    

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37. Storing time:
    1521261900
    >1970-01-01T00:00:00+00:00
    <2038-01-19T03:14:07+00:00 (32bit)
    

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38. Storing time:
    RFC3339:
    2018-03-17T10:15:00+05:30
    

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39. Storing time:
    RFC3339 extended:
    2018-03-17T10:15:00.000+05:30
    

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40. Storing time:
    Sortable (in UTC):
    2018-03-17T05:45:00.000+00:00
    

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41. Storing time:
    Sortable (in UTC):
    2018-03-17T05:45:00.000+00:00
    + user’s location for timezone & locale
    

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42. Storing time:
    Sortable (in UTC):
    2018-03-17T05:45:00.000+00:00
    + user’s location for timezone & locale
    (europe/brussels)
    

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43. Time in PHP
    

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44. date()
    microtime()
    

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45. DateTimeInterface
    - DateTime (date, time, tz)
    - DateTimeImmutable
    

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46. $date = DateTimeImmutable::createFromMutable($mutable);
    

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47. Change in PHP 7.1: microseconds
    

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48. // <7.1
    $date = new DateTimeImmutable(‘now’);
    $date->format(‘u’); // 00000
    // 7.1+
    $date = new DateTimeImmutable(‘now’);
    $date->format(‘u’); // actual microsecond info
    

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49. $date = $date->setTimezone('Europe/Rome');
    

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50. // Magic
    $date = new DateTimeImmutable('now');
    $date = $date->modify('first day of next month');
    

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51. “now + 5 hours”
    “first day of next month”
    "first weekday”
    …
    

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52. “2016-03-00” → “2016-02-29”
    “2018-06-31” → “2018-07-01”
    …
    

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53. “69-12-31” → “2069-12-31”
    “70-01-01” → “1970-01-01”
    …
    

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54. nesbot/carbon - Mutable
    cakephp/chronos - Immutable
    

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55. interface Clock
    {
    public function now(): DateTimeImmutable
    }
    class SystemClock implements Clock
    class TestClock implements Clock
    

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56. The future
    

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57. E=mc²
    

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58. c ~ 299.000.000m/s
    

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62. Wrapping up
    

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63. Thanks for your time!
    @hannesvdvreken
    @phpgent
    

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64. Time for questions.
    @hannesvdvreken
    @phpgent
    

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