chrono/src/lib.rs

// This is a part of rust-chrono.
// Copyright (c) 2014-2015, Kang Seonghoon.
// See README.md and LICENSE.txt for details.

//! # Chrono 0.2.18
//!
//! Date and time handling for Rust. (also known as `rust-chrono`)
//! It aims to be a feature-complete superset of
//! the [time](https://github.com/rust-lang/time) library.
//! In particular,
//!
//! * Chrono strictly adheres to ISO 8601.
//! * Chrono is timezone-aware by default, with separate timezone-naive types.
//! * Chrono is space-optimal and (while not being the primary goal) reasonably efficient.
//!
//! There were several previous attempts to bring a good date and time library to Rust,
//! which Chrono builts upon and should acknowledge:
//!
//! * [Initial research on
//!    the wiki](https://github.com/rust-lang/rust-wiki-backup/blob/master/Lib-datetime.md)
//! * Dietrich Epp's [datetime-rs](https://github.com/depp/datetime-rs)
//! * Luis de Bethencourt's [rust-datetime](https://github.com/luisbg/rust-datetime)
//!
//! ## Usage
//!
//! Put this in your `Cargo.toml`:
//!
//! ```toml
//! [dependencies]
//! chrono = "0.2"
//! ```
//!
//! And put this in your crate root:
//!
//! ```rust
//! extern crate chrono;
//! ```
//!
//! ## Overview
//!
//! ### Duration
//!
//! Chrono used to have a `Duration` type, which represents the time span.
//! This is a simple reexport of
//! [`time::Duration`](http://doc.rust-lang.org/time/time/struct.Duration.html) type
//! provided by crates.io `time` crate (which originally comes from Chrono).
//!
//! ### Date and Time
//!
//! Chrono provides a `DateTime` type for the combined date and time.
//!
//! `DateTime`, among others, is timezone-aware and
//! must be constructed from the `TimeZone` object.
//! `DateTime`s with different time zones do not mix, but can be converted to each other.
//!
//! You can get the current date and time in the UTC time zone (`UTC::now()`)
//! or in the local time zone (`Local::now()`).
//!
//! ~~~~ {.rust}
//! use chrono::*;
//!
//! let utc: DateTime<UTC> = UTC::now();       // e.g. `2014-11-28T12:45:59.324310806Z`
//! let local: DateTime<Local> = Local::now(); // e.g. `2014-11-28T21:45:59.324310806+09:00`
//! # let _ = utc; let _ = local;
//! ~~~~
//!
//! Alternatively, you can create your own date and time.
//! This is a bit verbose due to Rust's lack of function and method overloading,
//! but in turn we get a rich combination of initialization methods.
//!
//! ~~~~ {.rust}
//! use chrono::*;
//!
//! let dt = UTC.ymd(2014, 7, 8).and_hms(9, 10, 11); // `2014-07-08T09:10:11Z`
//! // July 8 is 188th day of the year 2014 (`o` for "ordinal")
//! assert_eq!(dt, UTC.yo(2014, 189).and_hms(9, 10, 11));
//! // July 8 is Tuesday in ISO week 28 of the year 2014.
//! assert_eq!(dt, UTC.isoywd(2014, 28, Weekday::Tue).and_hms(9, 10, 11));
//!
//! let dt = UTC.ymd(2014, 7, 8).and_hms_milli(9, 10, 11, 12); // `2014-07-08T09:10:11.012Z`
//! assert_eq!(dt, UTC.ymd(2014, 7, 8).and_hms_micro(9, 10, 11, 12_000));
//! assert_eq!(dt, UTC.ymd(2014, 7, 8).and_hms_nano(9, 10, 11, 12_000_000));
//!
//! // dynamic verification
//! assert_eq!(UTC.ymd_opt(2014, 7, 8).and_hms_opt(21, 15, 33),
//!            LocalResult::Single(UTC.ymd(2014, 7, 8).and_hms(21, 15, 33)));
//! assert_eq!(UTC.ymd_opt(2014, 7, 8).and_hms_opt(80, 15, 33), LocalResult::None);
//! assert_eq!(UTC.ymd_opt(2014, 7, 38).and_hms_opt(21, 15, 33), LocalResult::None);
//!
//! // other time zone objects can be used to construct a local datetime.
//! // obviously, `local_dt` is normally different from `dt`, but `fixed_dt` should be identical.
//! let local_dt = Local.ymd(2014, 7, 8).and_hms_milli(9, 10, 11, 12);
//! let fixed_dt = FixedOffset::east(9 * 3600).ymd(2014, 7, 8).and_hms_milli(18, 10, 11, 12);
//! assert_eq!(dt, fixed_dt);
//! # let _ = local_dt;
//! ~~~~
//!
//! Various properties are available to the date and time, and can be altered individually.
//! Most of them are defined in the traits `Datelike` and `Timelike` which you should `use` before.
//! Addition and subtraction is also supported.
//! The following illustrates most supported operations to the date and time:
//!
//! ~~~~ {.rust}
//! use chrono::*;
//!
//! # /* we intentionally fake the datetime...
//! // assume this returned `2014-11-28T21:45:59.324310806+09:00`:
//! let dt = Local::now();
//! # */ // up to here. we now define a fixed datetime for the illustrative purpose.
//! # let dt = FixedOffset::east(9*3600).ymd(2014, 11, 28).and_hms_nano(21, 45, 59, 324310806);
//!
//! // property accessors
//! assert_eq!((dt.year(), dt.month(), dt.day()), (2014, 11, 28));
//! assert_eq!((dt.month0(), dt.day0()), (10, 27)); // for unfortunate souls
//! assert_eq!((dt.hour(), dt.minute(), dt.second()), (21, 45, 59));
//! assert_eq!(dt.weekday(), Weekday::Fri);
//! assert_eq!(dt.weekday().number_from_monday(), 5); // Mon=1, ..., Sat=7
//! assert_eq!(dt.ordinal(), 332); // the day of year
//! assert_eq!(dt.num_days_from_ce(), 735565); // the number of days from and including Jan 1, 1
//!
//! // time zone accessor and manipulation
//! assert_eq!(dt.offset().local_minus_utc(), Duration::hours(9));
//! assert_eq!(dt.timezone(), FixedOffset::east(9 * 3600));
//! assert_eq!(dt.with_timezone(&UTC), UTC.ymd(2014, 11, 28).and_hms_nano(12, 45, 59, 324310806));
//!
//! // a sample of property manipulations (validates dynamically)
//! assert_eq!(dt.with_day(29).unwrap().weekday(), Weekday::Sat); // 2014-11-29 is Saturday
//! assert_eq!(dt.with_day(32), None);
//! assert_eq!(dt.with_year(-300).unwrap().num_days_from_ce(), -109606); // November 29, 301 BCE
//!
//! // arithmetic operations
//! assert_eq!(UTC.ymd(2014, 11, 14).and_hms(8, 9, 10) - UTC.ymd(2014, 11, 14).and_hms(10, 9, 8),
//!            Duration::seconds(-2 * 3600 + 2));
//! assert_eq!(UTC.ymd(1970, 1, 1).and_hms(0, 0, 0) + Duration::seconds(1_000_000_000),
//!            UTC.ymd(2001, 9, 9).and_hms(1, 46, 40));
//! assert_eq!(UTC.ymd(1970, 1, 1).and_hms(0, 0, 0) - Duration::seconds(1_000_000_000),
//!            UTC.ymd(1938, 4, 24).and_hms(22, 13, 20));
//! ~~~~
//!
//! Formatting is done via the `format` method,
//! which format is equivalent to the familiar `strftime` format.
//! (See the `format::strftime` module documentation for full syntax.)
//!
//! The default `to_string` method and `{:?}` specifier also give a reasonable representation.
//! Chrono also provides `to_rfc{2822,3339}` methods for well-known formats.
//!
//! ~~~~ {.rust}
//! use chrono::*;
//!
//! let dt = UTC.ymd(2014, 11, 28).and_hms(12, 0, 9);
//! assert_eq!(dt.format("%Y-%m-%d %H:%M:%S").to_string(), "2014-11-28 12:00:09");
//! assert_eq!(dt.format("%a %b %e %T %Y").to_string(), "Fri Nov 28 12:00:09 2014");
//! assert_eq!(dt.format("%a %b %e %T %Y").to_string(), dt.format("%c").to_string());
//!
//! assert_eq!(dt.to_string(), "2014-11-28 12:00:09 UTC");
//! assert_eq!(dt.to_rfc2822(), "Fri, 28 Nov 2014 12:00:09 +0000");
//! assert_eq!(dt.to_rfc3339(), "2014-11-28T12:00:09+00:00");
//! assert_eq!(format!("{:?}", dt), "2014-11-28T12:00:09Z");
//! ~~~~
//!
//! Parsing can be done with three methods:
//!
//! 1. The standard `FromStr` trait (and `parse` method on a string) can be used for
//!    parsing `DateTime<FixedOffset>`, `DateTime<UTC>` and `DateTime<Local>` values.
//!    This parses what the `{:?}` (`std::fmt::Debug`) format specifier prints,
//!    and requires the offset to be present.
//!
//! 2. `DateTime::parse_from_str` parses a date and time with offsets and
//!    returns `DateTime<FixedOffset>`.
//!    This should be used when the offset is a part of input and the caller cannot guess that.
//!    It *cannot* be used when the offset can be missing.
//!    `DateTime::parse_from_rfc{2822,3339}` are similar but for well-known formats.
//!
//! 3. `Offset::datetime_from_str` is similar but returns `DateTime` of given offset.
//!    When the explicit offset is missing from the input, it simply uses given offset.
//!    It issues an error when the input contains an explicit offset different
//!    from the current offset.
//!
//! More detailed control over the parsing process is available via `format` module.
//!
//! ~~~~ {.rust}
//! use chrono::*;
//!
//! let dt = UTC.ymd(2014, 11, 28).and_hms(12, 0, 9);
//! let fixed_dt = dt.with_timezone(&FixedOffset::east(9*3600));
//!
//! // method 1
//! assert_eq!("2014-11-28T12:00:09Z".parse::<DateTime<UTC>>(), Ok(dt.clone()));
//! assert_eq!("2014-11-28T21:00:09+09:00".parse::<DateTime<UTC>>(), Ok(dt.clone()));
//! assert_eq!("2014-11-28T21:00:09+09:00".parse::<DateTime<FixedOffset>>(), Ok(fixed_dt.clone()));
//!
//! // method 2
//! assert_eq!(DateTime::parse_from_str("2014-11-28 21:00:09 +09:00", "%Y-%m-%d %H:%M:%S %z"),
//!            Ok(fixed_dt.clone()));
//! assert_eq!(DateTime::parse_from_rfc2822("Fri, 28 Nov 2014 21:00:09 +0900"),
//!            Ok(fixed_dt.clone()));
//! assert_eq!(DateTime::parse_from_rfc3339("2014-11-28T21:00:09+09:00"), Ok(fixed_dt.clone()));
//!
//! // method 3
//! assert_eq!(UTC.datetime_from_str("2014-11-28 12:00:09", "%Y-%m-%d %H:%M:%S"), Ok(dt.clone()));
//! assert_eq!(UTC.datetime_from_str("Fri Nov 28 12:00:09 2014", "%a %b %e %T %Y"), Ok(dt.clone()));
//!
//! // oops, the year is missing!
//! assert!(UTC.datetime_from_str("Fri Nov 28 12:00:09", "%a %b %e %T %Y").is_err());
//! // oops, the format string does not include the year at all!
//! assert!(UTC.datetime_from_str("Fri Nov 28 12:00:09", "%a %b %e %T").is_err());
//! // oops, the weekday is incorrect!
//! assert!(UTC.datetime_from_str("Sat Nov 28 12:00:09 2014", "%a %b %e %T %Y").is_err());
//! ~~~~
//!
//! ### Individual date
//!
//! Chrono also provides an individual date type (`Date`).
//! It also has time zones attached, and have to be constructed via time zones.
//! Most operations available to `DateTime` are also available to `Date` whenever appropriate.
//!
//! ~~~~ {.rust}
//! use chrono::*;
//!
//! # // these *may* fail, but only very rarely. just rerun the test if you were that unfortunate ;)
//! assert_eq!(UTC::today(), UTC::now().date());
//! assert_eq!(Local::today(), Local::now().date());
//!
//! assert_eq!(UTC.ymd(2014, 11, 28).weekday(), Weekday::Fri);
//! assert_eq!(UTC.ymd_opt(2014, 11, 31), LocalResult::None);
//! assert_eq!(UTC.ymd(2014, 11, 28).and_hms_milli(7, 8, 9, 10).format("%H%M%S").to_string(),
//!            "070809");
//! ~~~~
//!
//! There is no timezone-aware `Time` due to the lack of usefulness and also the complexity.
//!
//! `DateTime` has `date` method which returns a `Date` which represents its date component.
//! There is also a `time` method, which simply returns a naive local time described below.
//!
//! ### Naive date and time
//!
//! Chrono provides naive counterparts to `Date`, (non-existent) `Time` and `DateTime`
//! as `NaiveDate`, `NaiveTime` and `NaiveDateTime` respectively.
//!
//! They have almost equivalent interfaces as their timezone-aware twins,
//! but are not associated to time zones obviously and can be quite low-level.
//! They are mostly useful for building blocks for higher-level types.
//!
//! Timezone-aware `DateTime` and `Date` types have two methods returning naive versions:
//! `naive_local` returns a view to the naive local time,
//! and `naive_utc` returns a view to the naive UTC time.
//!
//! ## Limitations
//!
//! Only proleptic Gregorian calendar (i.e. extended to support older dates) is supported.
//! Be very careful if you really have to deal with pre-20C dates, they can be in Julian or others.
//!
//! Date types are limited in about +/- 262,000 years from the common epoch.
//! Time types are limited in the nanosecond accuracy.
//!
//! Leap seconds are supported in the representation but Chrono doesn't try to make use of them.
//! (The main reason is that leap seconds are not really predictable.)
//! Almost *every* operation over the possible leap seconds will ignore them.
//! Consider using `NaiveDateTime` with the implicit TAI (International Atomic Time) scale
//! if you want.
//!
//! Chrono inherently does not support an inaccurate or partial date and time representation.
//! Any operation that can be ambiguous will return `None` in such cases.
//! For example, "a month later" of 2014-01-30 is not well-defined
//! and consequently `UTC.ymd(2014, 1, 30).with_month(2)` returns `None`.
//!
//! Advanced time zone handling is not yet supported (but is planned in 0.3).

#![doc(html_root_url = "https://lifthrasiir.github.io/rust-chrono/")]

#![cfg_attr(bench, feature(test))] // lib stability features as per RFC #507
#![deny(missing_docs)]

extern crate time as stdtime;
extern crate num;
#[cfg(feature = "rustc-serialize")]
extern crate rustc_serialize;
#[cfg(feature = "serde")]
extern crate serde;

pub use duration::Duration;
pub use offset::{TimeZone, Offset, LocalResult};
pub use offset::utc::UTC;
pub use offset::fixed::FixedOffset;
pub use offset::local::Local;
pub use naive::date::NaiveDate;
pub use naive::time::NaiveTime;
pub use naive::datetime::NaiveDateTime;
pub use date::Date;
pub use datetime::DateTime;
pub use format::{ParseError, ParseResult};

// useful throughout the codebase
macro_rules! try_opt {
    ($e:expr) => (match $e { Some(v) => v, None => return None })
}

mod div;
pub mod duration {
    //! ISO 8601 duration.
    //!
    //! This used to be a part of rust-chrono,
    //! but has been subsequently merged into Rust's standard library.
    pub use stdtime::Duration;
}
pub mod offset;
pub mod naive {
    //! Date and time types which do not concern about the timezones.
    //!
    //! They are primarily building blocks for other types (e.g. `TimeZone`),
    //! but can be also used for the simpler date and time handling.
    pub mod date;
    pub mod time;
    pub mod datetime;
}
pub mod date;
pub mod datetime;
pub mod format;

/// The day of week (DOW).
///
/// The order of the days of week depends on the context.
/// One should prefer `*_from_monday` or `*_from_sunday` methods to get the correct result.
#[derive(PartialEq, Eq, Copy, Clone, Debug)]
#[cfg_attr(feature = "rustc-serialize", derive(RustcEncodable, RustcDecodable))]
pub enum Weekday {
    /// Monday.
    Mon = 0,
    /// Tuesday.
    Tue = 1,
    /// Wednesday.
    Wed = 2,
    /// Thursday.
    Thu = 3,
    /// Friday.
    Fri = 4,
    /// Saturday.
    Sat = 5,
    /// Sunday.
    Sun = 6,
}

impl Weekday {
    /// The next day in the week.
    #[inline]
    pub fn succ(&self) -> Weekday {
        match *self {
            Weekday::Mon => Weekday::Tue,
            Weekday::Tue => Weekday::Wed,
            Weekday::Wed => Weekday::Thu,
            Weekday::Thu => Weekday::Fri,
            Weekday::Fri => Weekday::Sat,
            Weekday::Sat => Weekday::Sun,
            Weekday::Sun => Weekday::Mon,
        }
    }

    /// The previous day in the week.
    #[inline]
    pub fn pred(&self) -> Weekday {
        match *self {
            Weekday::Mon => Weekday::Sun,
            Weekday::Tue => Weekday::Mon,
            Weekday::Wed => Weekday::Tue,
            Weekday::Thu => Weekday::Wed,
            Weekday::Fri => Weekday::Thu,
            Weekday::Sat => Weekday::Fri,
            Weekday::Sun => Weekday::Sat,
        }
    }

    /// Returns a DOW number starting from Monday = 1. (ISO 8601 weekday number)
    #[inline]
    pub fn number_from_monday(&self) -> u32 {
        match *self {
            Weekday::Mon => 1,
            Weekday::Tue => 2,
            Weekday::Wed => 3,
            Weekday::Thu => 4,
            Weekday::Fri => 5,
            Weekday::Sat => 6,
            Weekday::Sun => 7,
        }
    }

    /// Returns a DOW number starting from Sunday = 1.
    #[inline]
    pub fn number_from_sunday(&self) -> u32 {
        match *self {
            Weekday::Mon => 2,
            Weekday::Tue => 3,
            Weekday::Wed => 4,
            Weekday::Thu => 5,
            Weekday::Fri => 6,
            Weekday::Sat => 7,
            Weekday::Sun => 1,
        }
    }

    /// Returns a DOW number starting from Monday = 0.
    #[inline]
    pub fn num_days_from_monday(&self) -> u32 {
        match *self {
            Weekday::Mon => 0,
            Weekday::Tue => 1,
            Weekday::Wed => 2,
            Weekday::Thu => 3,
            Weekday::Fri => 4,
            Weekday::Sat => 5,
            Weekday::Sun => 6,
        }
    }

    /// Returns a DOW number starting from Sunday = 0.
    #[inline]
    pub fn num_days_from_sunday(&self) -> u32 {
        match *self {
            Weekday::Mon => 1,
            Weekday::Tue => 2,
            Weekday::Wed => 3,
            Weekday::Thu => 4,
            Weekday::Fri => 5,
            Weekday::Sat => 6,
            Weekday::Sun => 0,
        }
    }
}

/// Any weekday can be represented as an integer from 0 to 6,
/// which equals to `Weekday::num_days_from_monday` in this implementation.
/// Do not heavily depend on this though; use explicit methods whenever possible.
impl num::traits::FromPrimitive for Weekday {
    #[inline]
    fn from_i64(n: i64) -> Option<Weekday> {
        match n {
            0 => Some(Weekday::Mon),
            1 => Some(Weekday::Tue),
            2 => Some(Weekday::Wed),
            3 => Some(Weekday::Thu),
            4 => Some(Weekday::Fri),
            5 => Some(Weekday::Sat),
            6 => Some(Weekday::Sun),
            _ => None,
        }
    }

    #[inline]
    fn from_u64(n: u64) -> Option<Weekday> {
        match n {
            0 => Some(Weekday::Mon),
            1 => Some(Weekday::Tue),
            2 => Some(Weekday::Wed),
            3 => Some(Weekday::Thu),
            4 => Some(Weekday::Fri),
            5 => Some(Weekday::Sat),
            6 => Some(Weekday::Sun),
            _ => None,
        }
    }
}


/// The common set of methods for date component.
pub trait Datelike: Sized {
    /// Returns the year number.
    fn year(&self) -> i32;

    /// Returns the absolute year number starting from 1 with a boolean flag,
    /// which is false when the year predates the epoch (BCE/BC) and true otherwise (CE/AD).
    #[inline]
    fn year_ce(&self) -> (bool, u32) {
        let year = self.year();
        if year < 1 {
            (false, (1 - year) as u32)
        } else {
            (true, year as u32)
        }
    }

    /// Returns the month number starting from 1.
    fn month(&self) -> u32;

    /// Returns the month number starting from 0.
    fn month0(&self) -> u32;

    /// Returns the day of month starting from 1.
    fn day(&self) -> u32;

    /// Returns the day of month starting from 0.
    fn day0(&self) -> u32;

    /// Returns the day of year starting from 1.
    fn ordinal(&self) -> u32;

    /// Returns the day of year starting from 0.
    fn ordinal0(&self) -> u32;

    /// Returns the day of week.
    fn weekday(&self) -> Weekday;

    /// Returns the ISO week date: an adjusted year, week number and day of week.
    /// The adjusted year may differ from that of the calendar date.
    fn isoweekdate(&self) -> (i32, u32, Weekday);

    /// Makes a new value with the year number changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_year(&self, year: i32) -> Option<Self>;

    /// Makes a new value with the month number (starting from 1) changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_month(&self, month: u32) -> Option<Self>;

    /// Makes a new value with the month number (starting from 0) changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_month0(&self, month0: u32) -> Option<Self>;

    /// Makes a new value with the day of month (starting from 1) changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_day(&self, day: u32) -> Option<Self>;

    /// Makes a new value with the day of month (starting from 0) changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_day0(&self, day0: u32) -> Option<Self>;

    /// Makes a new value with the day of year (starting from 1) changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_ordinal(&self, ordinal: u32) -> Option<Self>;

    /// Makes a new value with the day of year (starting from 0) changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_ordinal0(&self, ordinal0: u32) -> Option<Self>;

    /// Returns the number of days since January 1, 1 (Day 1) in the proleptic Gregorian calendar.
    fn num_days_from_ce(&self) -> i32 {
        // we know this wouldn't overflow since year is limited to 1/2^13 of i32's full range.
        let mut year = self.year() - 1;
        let mut ndays = 0;
        if year < 0 {
            let excess = 1 + (-year) / 400;
            year += excess * 400;
            ndays -= excess * 146097;
        }
        let div_100 = year / 100;
        ndays += ((year * 1461) >> 2) - div_100 + (div_100 >> 2);
        ndays + self.ordinal() as i32
    }
}

/// The common set of methods for time component.
pub trait Timelike: Sized {
    /// Returns the hour number from 0 to 23.
    fn hour(&self) -> u32;

    /// Returns the hour number from 1 to 12 with a boolean flag,
    /// which is false for AM and true for PM.
    #[inline]
    fn hour12(&self) -> (bool, u32) {
        let hour = self.hour();
        let mut hour12 = hour % 12;
        if hour12 == 0 {
            hour12 = 12;
        }
        (hour >= 12, hour12)
    }

    /// Returns the minute number from 0 to 59.
    fn minute(&self) -> u32;

    /// Returns the second number from 0 to 59.
    fn second(&self) -> u32;

    /// Returns the number of nanoseconds since the whole non-leap second.
    /// The range from 1,000,000,000 to 1,999,999,999 represents the leap second.
    fn nanosecond(&self) -> u32;

    /// Makes a new value with the hour number changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_hour(&self, hour: u32) -> Option<Self>;

    /// Makes a new value with the minute number changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_minute(&self, min: u32) -> Option<Self>;

    /// Makes a new value with the second number changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_second(&self, sec: u32) -> Option<Self>;

    /// Makes a new value with nanoseconds since the whole non-leap second changed.
    ///
    /// Returns `None` when the resulting value would be invalid.
    fn with_nanosecond(&self, nano: u32) -> Option<Self>;

    /// Returns the number of non-leap seconds past the last midnight.
    #[inline]
    fn num_seconds_from_midnight(&self) -> u32 {
        self.hour() * 3600 + self.minute() * 60 + self.second()
    }
}

#[test]
fn test_readme_doomsday() {
    use num::iter::range_inclusive;

    for y in range_inclusive(naive::date::MIN.year(), naive::date::MAX.year()) {
        // even months
        let d4 = NaiveDate::from_ymd(y, 4, 4);
        let d6 = NaiveDate::from_ymd(y, 6, 6);
        let d8 = NaiveDate::from_ymd(y, 8, 8);
        let d10 = NaiveDate::from_ymd(y, 10, 10);
        let d12 = NaiveDate::from_ymd(y, 12, 12);

        // nine to five, seven-eleven
        let d59 = NaiveDate::from_ymd(y, 5, 9);
        let d95 = NaiveDate::from_ymd(y, 9, 5);
        let d711 = NaiveDate::from_ymd(y, 7, 11);
        let d117 = NaiveDate::from_ymd(y, 11, 7);

        // "March 0"
        let d30 = NaiveDate::from_ymd(y, 3, 1).pred();

        let weekday = d30.weekday();
        let other_dates = [d4, d6, d8, d10, d12, d59, d95, d711, d117];
        assert!(other_dates.iter().all(|d| d.weekday() == weekday));
    }
}