diff options
Diffstat (limited to 'absl/time/time.h')
| -rw-r--r-- | absl/time/time.h | 40 |
1 files changed, 39 insertions, 1 deletions
diff --git a/absl/time/time.h b/absl/time/time.h index 2858da2955f6..7d5c3fde7a61 100644 --- a/absl/time/time.h +++ b/absl/time/time.h @@ -886,7 +886,7 @@ class TimeZone { struct TimeInfo { enum CivilKind { UNIQUE, // the civil time was singular (pre == trans == post) - SKIPPED, // the civil time did not exist (pre => trans > post) + SKIPPED, // the civil time did not exist (pre >= trans > post) REPEATED, // the civil time was ambiguous (pre < trans <= post) } kind; Time pre; // time calculated using the pre-transition offset @@ -925,6 +925,44 @@ class TimeZone { // // nov06.post is 2011-11-06 01:15:00 -0800 TimeInfo At(CivilSecond ct) const; + // TimeZone::NextTransition() + // TimeZone::PrevTransition() + // + // Finds the time of the next/previous offset change in this time zone. + // + // By definition, `NextTransition(t, &trans)` returns false when `t` is + // `InfiniteFuture()`, and `PrevTransition(t, &trans)` returns false + // when `t` is `InfinitePast()`. If the zone has no transitions, the + // result will also be false no matter what the argument. + // + // Otherwise, when `t` is `InfinitePast()`, `NextTransition(t, &trans)` + // returns true and sets `trans` to the first recorded transition. Chains + // of calls to `NextTransition()/PrevTransition()` will eventually return + // false, but it is unspecified exactly when `NextTransition(t, &trans)` + // jumps to false, or what time is set by `PrevTransition(t, &trans)` for + // a very distant `t`. + // + // Note: Enumeration of time-zone transitions is for informational purposes + // only. Modern time-related code should not care about when offset changes + // occur. + // + // Example: + // absl::TimeZone nyc; + // if (!absl::LoadTimeZone("America/New_York", &nyc)) { ... } + // const auto now = absl::Now(); + // auto t = absl::InfinitePast(); + // absl::TimeZone::CivilTransition trans; + // while (t <= now && nyc.NextTransition(t, &trans)) { + // // transition: trans.from -> trans.to + // t = nyc.At(trans.to).trans; + // } + struct CivilTransition { + CivilSecond from; // the civil time we jump from + CivilSecond to; // the civil time we jump to + }; + bool NextTransition(Time t, CivilTransition* trans) const; + bool PrevTransition(Time t, CivilTransition* trans) const; + template <typename H> friend H AbslHashValue(H h, TimeZone tz) { return H::combine(std::move(h), tz.cz_); |