Slide 1
Slide 1 text
Which Time Is It?
Slide 2
Slide 2 text
"Time" has many
meanings in English
Slide 3
Slide 3 text
Choosing the right time:
Better design and
avoids bugs
Slide 4
Slide 4 text
What is the
difference
between 1.day
and 1.day.ago?
Slide 5
Slide 5 text
Two Kinds of Time
Moment
November 14th, 2023 at 10:30AM PST
Duration
45 minutes
Slide 6
Slide 6 text
Visualizing the difference
Slide 7
Slide 7 text
Timeline
Slide 8
Slide 8 text
Moment
Points on the timeline
Slide 9
Slide 9 text
Duration
Distance on the timeline
Slide 10
Slide 10 text
Not 1d vectors!
Slide 11
Slide 11 text
CLASSES PROVIDED BY
Ruby
Slide 12
Slide 12 text
MOMENT
DateTime
Slide 13
Slide 13 text
MOMENT
DateTime
Deprecated
Slide 14
Slide 14 text
MOMENT (NANOSECOND RESOLUTION)
Time
Nov 14, 2023 10:30:05.123456789 AM PST
Slide 15
Slide 15 text
Time
Nanoseconds apart
Slide 16
Slide 16 text
MOMENT (DAY RESOLUTION)
Date
Nov 14, 2023
Slide 17
Slide 17 text
Date
Days apart
Slide 18
Slide 18 text
Resolution impacts enumeration
start = Date.new(2023, 11, 12)
finish = Date.new(2023, 11, 15)
(start..finish).map(&:to_s)
# 2023-11-12
# 2023-11-13
# 2023-11-14
# 2023-11015
Slide 19
Slide 19 text
No content
Slide 20
Slide 20 text
Notice:
It's all the
same kind
of time!
Slide 21
Slide 21 text
Date/Time for moments and
numerics for durations
Core Ruby represents time with
Slide 22
Slide 22 text
Math!
Not all operations make sense
Slide 23
Slide 23 text
Time docs
Interesting method signatures
Slide 24
Slide 24 text
Time#+
time + numeric -> time
Slide 25
Slide 25 text
time + numeric -> time
Notice:
We can't
add two
time
instances!
Slide 26
Slide 26 text
What question is this asking?
Slide 27
Slide 27 text
What point is 45
mins after point A?
ADDITION IS ASKING:
Slide 28
Slide 28 text
Time#+
What point is 45 mins after point A?
Slide 29
Slide 29 text
Time#-
time - numeric -> time
time - other_time ->
float
Slide 30
Slide 30 text
Notice:
there are 2
signatures!
Slide 31
Slide 31 text
What questions is this asking?
Slide 32
Slide 32 text
What point is 45 mins
before point A?
SUBTRACTION IS ASKING:
Slide 33
Slide 33 text
time - numeric -> time
What point is 45 mins before point A?
Slide 34
Slide 34 text
time - time -> float
Notice:
we can
subtract
two points!
Slide 35
Slide 35 text
What questions is this asking?
Slide 36
Slide 36 text
How big is the duration
between points A and B?
SUBTRACTION IS ASKING:
Slide 37
Slide 37 text
time - time -> float
What is the distance between points A and B?
Slide 38
Slide 38 text
3 questions
we can
answer
about the
same data
Slide 39
Slide 39 text
Same equation, rearanged
point1 + duration = point2 (Time#+)
point2 - duration = point1 (Time#- v1)
point2 - point1 = duration (Time#- v2)
Slide 40
Slide 40 text
What it you need a
time without an
associated day?
Slide 41
Slide 41 text
Other Kinds of Time
Moment
November 14th, 2023 at 11:30AM PST
Duration
45 minutes
Time of Day
5:30 PM
Slide 42
Slide 42 text
Time of Day
Points on a circular timeline
Slide 43
Slide 43 text
How does ToD interact
with other types?
Slide 44
Slide 44 text
Time of Day
Our 3 questions still work!
Slide 45
Slide 45 text
Extract from a Time
Slide 46
Slide 46 text
Combine ToD with
Date to get a Time
Slide 47
Slide 47 text
Third Party Solutions
GEMS!
Slide 48
Slide 48 text
DURATION
ActiveSupport
third party gems
Slide 49
Slide 49 text
DURATION
1.day
Slide 50
Slide 50 text
POINT IN TIME
1.day.ago
Slide 51
Slide 51 text
Sugar
Time.now - (1 * SECONDS_PER_DAY)
Slide 52
Slide 52 text
TIME OF DAY
jackc/tod
third party gems
Slide 53
Slide 53 text
How to Implement Time?
Slide 54
Slide 54 text
Warning
Slide 55
Slide 55 text
Avoid human-readable integers like 1030
Slide 56
Slide 56 text
Invalid times like 3176
Slide 57
Slide 57 text
Breaks Math (1025 - 0925 = 100)
Slide 58
Slide 58 text
Avoid multi-part values
like {hour: 10, minute: 30}
Slide 59
Slide 59 text
Epoch + Counter
Slide 60
Slide 60 text
Epoch: when is 0?
Slide 61
Slide 61 text
Counter: how many
since 0?
Slide 62
Slide 62 text
Common Implementations
UNIX Time
milliseconds since Jan 1, 1970
Postgres Time of Day
microseconds since midnight
Ruby Date
days since Jan 1, 4713 BCE
Slide 63
Slide 63 text
Just a big counter
class TimeOfDay
def initialize(microseconds_since_midnight)
@counter =
(microseconconds_since_midnight % MS_PER_DAY)
end
end
Slide 64
Slide 64 text
Custom constructor
class TimeOfDay
def self.from_parts(hours:, minutes:, seconds:)
total =
(hours * MICROSECONDS_PER_HOUR) +
(minutes * MICROSECONDS_PER_MINUTE) +
(seconds * MICROSECONDS_PER_SECOND)
new(total)
end
end
Slide 65
Slide 65 text
Operators
class TimeOfDay
def +(duration_microseconds)
self.class.new(@counter + duration_microseconds)
end
end
Slide 66
Slide 66 text
Case Study
Slide 67
Slide 67 text
No content
Slide 68
Slide 68 text
When working with time
Think About
What kind of time you need
moment, duration, tod, etc
What operations make sense
(and which ones don't!)
both within and across types
What resolution you need
e.g. Time vs Date class
Slide 69
Slide 69 text
Joël Quenneville
Joël Quenneville
Principal Developer
thoughtbot
@joelquen
bikeshed.fm
co-host