| // Copyright 2016 Google Inc. All Rights Reserved. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| #ifndef ABSL_TIME_INTERNAL_CCTZ_CIVIL_TIME_H_ |
| #define ABSL_TIME_INTERNAL_CCTZ_CIVIL_TIME_H_ |
| |
| #include "absl/base/config.h" |
| #include "absl/time/internal/cctz/include/cctz/civil_time_detail.h" |
| |
| namespace absl { |
| ABSL_NAMESPACE_BEGIN |
| namespace time_internal { |
| namespace cctz { |
| |
| // The term "civil time" refers to the legally recognized human-scale time |
| // that is represented by the six fields YYYY-MM-DD hh:mm:ss. Modern-day civil |
| // time follows the Gregorian Calendar and is a time-zone-independent concept. |
| // A "date" is perhaps the most common example of a civil time (represented in |
| // this library as cctz::civil_day). This library provides six classes and a |
| // handful of functions that help with rounding, iterating, and arithmetic on |
| // civil times while avoiding complications like daylight-saving time (DST). |
| // |
| // The following six classes form the core of this civil-time library: |
| // |
| // * civil_second |
| // * civil_minute |
| // * civil_hour |
| // * civil_day |
| // * civil_month |
| // * civil_year |
| // |
| // Each class is a simple value type with the same interface for construction |
| // and the same six accessors for each of the civil fields (year, month, day, |
| // hour, minute, and second, aka YMDHMS). These classes differ only in their |
| // alignment, which is indicated by the type name and specifies the field on |
| // which arithmetic operates. |
| // |
| // Each class can be constructed by passing up to six optional integer |
| // arguments representing the YMDHMS fields (in that order) to the |
| // constructor. Omitted fields are assigned their minimum valid value. Hours, |
| // minutes, and seconds will be set to 0, month and day will be set to 1, and |
| // since there is no minimum valid year, it will be set to 1970. So, a |
| // default-constructed civil-time object will have YMDHMS fields representing |
| // "1970-01-01 00:00:00". Fields that are out-of-range are normalized (e.g., |
| // October 32 -> November 1) so that all civil-time objects represent valid |
| // values. |
| // |
| // Each civil-time class is aligned to the civil-time field indicated in the |
| // class's name after normalization. Alignment is performed by setting all the |
| // inferior fields to their minimum valid value (as described above). The |
| // following are examples of how each of the six types would align the fields |
| // representing November 22, 2015 at 12:34:56 in the afternoon. (Note: the |
| // string format used here is not important; it's just a shorthand way of |
| // showing the six YMDHMS fields.) |
| // |
| // civil_second 2015-11-22 12:34:56 |
| // civil_minute 2015-11-22 12:34:00 |
| // civil_hour 2015-11-22 12:00:00 |
| // civil_day 2015-11-22 00:00:00 |
| // civil_month 2015-11-01 00:00:00 |
| // civil_year 2015-01-01 00:00:00 |
| // |
| // Each civil-time type performs arithmetic on the field to which it is |
| // aligned. This means that adding 1 to a civil_day increments the day field |
| // (normalizing as necessary), and subtracting 7 from a civil_month operates |
| // on the month field (normalizing as necessary). All arithmetic produces a |
| // valid civil time. Difference requires two similarly aligned civil-time |
| // objects and returns the scalar answer in units of the objects' alignment. |
| // For example, the difference between two civil_hour objects will give an |
| // answer in units of civil hours. |
| // |
| // In addition to the six civil-time types just described, there are |
| // a handful of helper functions and algorithms for performing common |
| // calculations. These are described below. |
| // |
| // Note: In C++14 and later, this library is usable in a constexpr context. |
| // |
| // CONSTRUCTION: |
| // |
| // Each of the civil-time types can be constructed in two ways: by directly |
| // passing to the constructor up to six (optional) integers representing the |
| // YMDHMS fields, or by copying the YMDHMS fields from a differently aligned |
| // civil-time type. |
| // |
| // civil_day default_value; // 1970-01-01 00:00:00 |
| // |
| // civil_day a(2015, 2, 3); // 2015-02-03 00:00:00 |
| // civil_day b(2015, 2, 3, 4, 5, 6); // 2015-02-03 00:00:00 |
| // civil_day c(2015); // 2015-01-01 00:00:00 |
| // |
| // civil_second ss(2015, 2, 3, 4, 5, 6); // 2015-02-03 04:05:06 |
| // civil_minute mm(ss); // 2015-02-03 04:05:00 |
| // civil_hour hh(mm); // 2015-02-03 04:00:00 |
| // civil_day d(hh); // 2015-02-03 00:00:00 |
| // civil_month m(d); // 2015-02-01 00:00:00 |
| // civil_year y(m); // 2015-01-01 00:00:00 |
| // |
| // m = civil_month(y); // 2015-01-01 00:00:00 |
| // d = civil_day(m); // 2015-01-01 00:00:00 |
| // hh = civil_hour(d); // 2015-01-01 00:00:00 |
| // mm = civil_minute(hh); // 2015-01-01 00:00:00 |
| // ss = civil_second(mm); // 2015-01-01 00:00:00 |
| // |
| // ALIGNMENT CONVERSION: |
| // |
| // The alignment of a civil-time object cannot change, but the object may be |
| // used to construct a new object with a different alignment. This is referred |
| // to as "realigning". When realigning to a type with the same or more |
| // precision (e.g., civil_day -> civil_second), the conversion may be |
| // performed implicitly since no information is lost. However, if information |
| // could be discarded (e.g., civil_second -> civil_day), the conversion must |
| // be explicit at the call site. |
| // |
| // void fun(const civil_day& day); |
| // |
| // civil_second cs; |
| // fun(cs); // Won't compile because data may be discarded |
| // fun(civil_day(cs)); // OK: explicit conversion |
| // |
| // civil_day cd; |
| // fun(cd); // OK: no conversion needed |
| // |
| // civil_month cm; |
| // fun(cm); // OK: implicit conversion to civil_day |
| // |
| // NORMALIZATION: |
| // |
| // Integer arguments passed to the constructor may be out-of-range, in which |
| // case they are normalized to produce a valid civil-time object. This enables |
| // natural arithmetic on constructor arguments without worrying about the |
| // field's range. Normalization guarantees that there are no invalid |
| // civil-time objects. |
| // |
| // civil_day d(2016, 10, 32); // Out-of-range day; normalized to 2016-11-01 |
| // |
| // Note: If normalization is undesired, you can signal an error by comparing |
| // the constructor arguments to the normalized values returned by the YMDHMS |
| // properties. |
| // |
| // PROPERTIES: |
| // |
| // All civil-time types have accessors for all six of the civil-time fields: |
| // year, month, day, hour, minute, and second. Recall that fields inferior to |
| // the type's alignment will be set to their minimum valid value. |
| // |
| // civil_day d(2015, 6, 28); |
| // // d.year() == 2015 |
| // // d.month() == 6 |
| // // d.day() == 28 |
| // // d.hour() == 0 |
| // // d.minute() == 0 |
| // // d.second() == 0 |
| // |
| // COMPARISON: |
| // |
| // Comparison always considers all six YMDHMS fields, regardless of the type's |
| // alignment. Comparison between differently aligned civil-time types is |
| // allowed. |
| // |
| // civil_day feb_3(2015, 2, 3); // 2015-02-03 00:00:00 |
| // civil_day mar_4(2015, 3, 4); // 2015-03-04 00:00:00 |
| // // feb_3 < mar_4 |
| // // civil_year(feb_3) == civil_year(mar_4) |
| // |
| // civil_second feb_3_noon(2015, 2, 3, 12, 0, 0); // 2015-02-03 12:00:00 |
| // // feb_3 < feb_3_noon |
| // // feb_3 == civil_day(feb_3_noon) |
| // |
| // // Iterates all the days of February 2015. |
| // for (civil_day d(2015, 2, 1); d < civil_month(2015, 3); ++d) { |
| // // ... |
| // } |
| // |
| // STREAMING: |
| // |
| // Each civil-time type may be sent to an output stream using operator<<(). |
| // The output format follows the pattern "YYYY-MM-DDThh:mm:ss" where fields |
| // inferior to the type's alignment are omitted. |
| // |
| // civil_second cs(2015, 2, 3, 4, 5, 6); |
| // std::cout << cs << "\n"; // Outputs: 2015-02-03T04:05:06 |
| // |
| // civil_day cd(cs); |
| // std::cout << cd << "\n"; // Outputs: 2015-02-03 |
| // |
| // civil_year cy(cs); |
| // std::cout << cy << "\n"; // Outputs: 2015 |
| // |
| // ARITHMETIC: |
| // |
| // Civil-time types support natural arithmetic operators such as addition, |
| // subtraction, and difference. Arithmetic operates on the civil-time field |
| // indicated in the type's name. Difference requires arguments with the same |
| // alignment and returns the answer in units of the alignment. |
| // |
| // civil_day a(2015, 2, 3); |
| // ++a; // 2015-02-04 00:00:00 |
| // --a; // 2015-02-03 00:00:00 |
| // civil_day b = a + 1; // 2015-02-04 00:00:00 |
| // civil_day c = 1 + b; // 2015-02-05 00:00:00 |
| // int n = c - a; // n = 2 (civil days) |
| // int m = c - civil_month(c); // Won't compile: different types. |
| // |
| // EXAMPLE: Adding a month to January 31. |
| // |
| // One of the classic questions that arises when considering a civil-time |
| // library (or a date library or a date/time library) is this: "What happens |
| // when you add a month to January 31?" This is an interesting question |
| // because there could be a number of possible answers: |
| // |
| // 1. March 3 (or 2 if a leap year). This may make sense if the operation |
| // wants the equivalent of February 31. |
| // 2. February 28 (or 29 if a leap year). This may make sense if the operation |
| // wants the last day of January to go to the last day of February. |
| // 3. Error. The caller may get some error, an exception, an invalid date |
| // object, or maybe false is returned. This may make sense because there is |
| // no single unambiguously correct answer to the question. |
| // |
| // Practically speaking, any answer that is not what the programmer intended |
| // is the wrong answer. |
| // |
| // This civil-time library avoids the problem by making it impossible to ask |
| // ambiguous questions. All civil-time objects are aligned to a particular |
| // civil-field boundary (such as aligned to a year, month, day, hour, minute, |
| // or second), and arithmetic operates on the field to which the object is |
| // aligned. This means that in order to "add a month" the object must first be |
| // aligned to a month boundary, which is equivalent to the first day of that |
| // month. |
| // |
| // Of course, there are ways to compute an answer the question at hand using |
| // this civil-time library, but they require the programmer to be explicit |
| // about the answer they expect. To illustrate, let's see how to compute all |
| // three of the above possible answers to the question of "Jan 31 plus 1 |
| // month": |
| // |
| // const civil_day d(2015, 1, 31); |
| // |
| // // Answer 1: |
| // // Add 1 to the month field in the constructor, and rely on normalization. |
| // const auto ans_normalized = civil_day(d.year(), d.month() + 1, d.day()); |
| // // ans_normalized == 2015-03-03 (aka Feb 31) |
| // |
| // // Answer 2: |
| // // Add 1 to month field, capping to the end of next month. |
| // const auto next_month = civil_month(d) + 1; |
| // const auto last_day_of_next_month = civil_day(next_month + 1) - 1; |
| // const auto ans_capped = std::min(ans_normalized, last_day_of_next_month); |
| // // ans_capped == 2015-02-28 |
| // |
| // // Answer 3: |
| // // Signal an error if the normalized answer is not in next month. |
| // if (civil_month(ans_normalized) != next_month) { |
| // // error, month overflow |
| // } |
| // |
| using civil_year = detail::civil_year; |
| using civil_month = detail::civil_month; |
| using civil_day = detail::civil_day; |
| using civil_hour = detail::civil_hour; |
| using civil_minute = detail::civil_minute; |
| using civil_second = detail::civil_second; |
| |
| // An enum class with members monday, tuesday, wednesday, thursday, friday, |
| // saturday, and sunday. These enum values may be sent to an output stream |
| // using operator<<(). The result is the full weekday name in English with a |
| // leading capital letter. |
| // |
| // weekday wd = weekday::thursday; |
| // std::cout << wd << "\n"; // Outputs: Thursday |
| // |
| using detail::weekday; |
| |
| // Returns the weekday for the given civil-time value. |
| // |
| // civil_day a(2015, 8, 13); |
| // weekday wd = get_weekday(a); // wd == weekday::thursday |
| // |
| using detail::get_weekday; |
| |
| // Returns the civil_day that strictly follows or precedes the given |
| // civil_day, and that falls on the given weekday. |
| // |
| // For example, given: |
| // |
| // August 2015 |
| // Su Mo Tu We Th Fr Sa |
| // 1 |
| // 2 3 4 5 6 7 8 |
| // 9 10 11 12 13 14 15 |
| // 16 17 18 19 20 21 22 |
| // 23 24 25 26 27 28 29 |
| // 30 31 |
| // |
| // civil_day a(2015, 8, 13); // get_weekday(a) == weekday::thursday |
| // civil_day b = next_weekday(a, weekday::thursday); // b = 2015-08-20 |
| // civil_day c = prev_weekday(a, weekday::thursday); // c = 2015-08-06 |
| // |
| // civil_day d = ... |
| // // Gets the following Thursday if d is not already Thursday |
| // civil_day thurs1 = next_weekday(d - 1, weekday::thursday); |
| // // Gets the previous Thursday if d is not already Thursday |
| // civil_day thurs2 = prev_weekday(d + 1, weekday::thursday); |
| // |
| using detail::next_weekday; |
| using detail::prev_weekday; |
| |
| // Returns the day-of-year for the given civil-time value. |
| // |
| // civil_day a(2015, 1, 1); |
| // int yd_jan_1 = get_yearday(a); // yd_jan_1 = 1 |
| // civil_day b(2015, 12, 31); |
| // int yd_dec_31 = get_yearday(b); // yd_dec_31 = 365 |
| // |
| using detail::get_yearday; |
| |
| } // namespace cctz |
| } // namespace time_internal |
| ABSL_NAMESPACE_END |
| } // namespace absl |
| |
| #endif // ABSL_TIME_INTERNAL_CCTZ_CIVIL_TIME_H_ |
