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side-by-side code changes report for "format-ddiff.th2m": 0.4.2_vs_0.4.3
1 [Format specs for durations]
3 Unlike time or absolute instants, durations are reference-free, i.e. the
4 reference instant is not part of the duration. As a result durations
5 cannot be named, i.e. there is no naming scheme that applies to all
6 durations and all references unambiguously.
8 Consequently, none of the format specifiers for date/times makes sense
9 for durations in the literal sense. However, to aid intuitive usage we
10 reused format specifiers when they represent integral values and a valid
11 unit for duration, as follows:
13 Date specs:
14 %c Equivalent to %w
15 %d Duration in days
16 %F Equivalent to %dd with no resorting to bigger units
17 %m Duration in months
18 %w Duration in weeks
19 %y Equivalent to %Y
20 %Y Duration in years
22 %db Duration in business days
23 %dB Equivalent to %db
25 Time specs:
26 %H Duration in hours
27 %I Equivalent to %H
28 %M Duration in minutes
29 %S Duration in seconds
30 %T Equivalent to %Ss without resorting to bigger units
32 %rS Duration in real-life seconds, as in including leap seconds
33 %rT Equivalent to %rSs without resorting to bigger units
35 General specs:
36 %n A newline character
37 %t A tab character
38 %% A literal % character
41 %r Modifier to turn units into real units
42 %0 Modifier to pad refined values with zeroes
43 %SPC Modifier to pad refined values with spaces
44 b Suffix, treat days as business days
47 [The refinement rule]
49 Durations are somewhat ambiguous when it comes to representing them
50 through format specifiers. Unlike format specifiers in point-in-time
51 representations duration specifiers can have an intra-line relationship.
53 So for instance a duration of 128 seconds might be presented through
54 "%S" as "128" but similarly through "%M:%S" as
55 "02:08" (read two minutes and 8 seconds).
57 There are several approaches to deal with this ambiguity. The ddiff
58 tool will follow, what we call, the refinement rule. That is,
59 regardless of the position of a format specifier, if it is a valid
60 /refinement/ of another specifier in the format string, then it
61 will only show the fractional value, i.e. the value in its natural range
62 with respect to the /refined/ specifier.
64 %Y possible refinements: %m, %w, %d
65 %m possible refinements: %w, %d
66 %w possible refinements: %d
67 %d possible refinements: %H, %M, %S
68 %H possible refinements: %M, %S
69 %M possible refinements: %S
71 The refinement alternatives are listed in order of precedence and they
72 are mutually exclusive. I.e. it is not possible to express a duration
73 in months and hours without having a "%d" specifier as well. On
74 the other hand in a chain of refinements inner elements are optional,
75 i.e. you can express a duration in weeks and hours because every day has
76 24 hours and hence there are 168 hours in a week.
78 In case of negative durations (the minuend is in the future relative to
79 the subtrahend) only the largest unit will carry the minus sign.
81 Using the refinement rule keeps the format string dead simple, there's
82 no need for operators or a full-blown language to distinguish the range
83 ambiguity, which then would have to be escaped because they could also
84 in theory be part of the literal characters of the format string,
85 resulting more often than not in command lines that are hard to craft
86 and even harder to understand later on (e.g. if used in shell scripts).
88 The refinement rule ingeniously covers the 99% case but, unlike other
89 approaches, there's no way to display two unrefined values in the
90 same format string, e.g. "'%w weeks (which is %d days)'".