Class XDateOnly

Extension methods for the DateOnly class.

Inheritance

System.Object

XDateOnly

Namespace: Galaxon.Core.Time

Assembly: Galaxon.Core.dll

Syntax

public static class XDateOnly : object

Methods

Add(DateOnly, TimeOnly)

Add a time of day to a date to find a new DateTime.

Declaration

public static DateTime Add(this DateOnly date, TimeOnly time)

Parameters

Type	Name	Description
DateOnly	date	The date.
TimeOnly	time	The time of day to add.

Returns

Type	Description
DateTime	The resulting DateTime.

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Add(DateOnly, TimeSpan)

Add a period of time to a date to find a new DateTime.

Declaration

public static DateTime Add(this DateOnly date, TimeSpan period)

Parameters

Type	Name	Description
DateOnly	date	The date.
TimeSpan	period	The time period to add.

Returns

Type	Description
DateTime	The resulting DateTime.

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AddWeeks(DateOnly, Int32)

Add a number of weeks to a date.

Declaration

public static DateOnly AddWeeks(this DateOnly date, int weeks)

Parameters

Type	Name	Description
DateOnly	date	The date.
System.Int32	weeks	The number of weeks to add.

Returns

Type	Description
DateOnly	The resulting date.

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FromDayOfYear(Int32, Int32)

Find a date given a year and the day of the year.

Formula from Meeus (Astronomical Algorithms 2 ed. p66).

Declaration

public static DateOnly FromDayOfYear(int year, int dayOfYear)

Parameters

Type	Name	Description
System.Int32	year	The year (1..9999).
System.Int32	dayOfYear	The day of the year (1..366).

Returns

Type	Description
DateOnly	The resulting date.

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FromJulianDay(Double)

Convert a Julian Day value to a date.

Declaration

public static DateOnly FromJulianDay(double jd)

Parameters

Type	Name	Description
System.Double	jd	The Julian Day value. If a fractional part indicating the time of day is included, this information will be discarded.

Returns

Type	Description
DateOnly	A new DateOnly object.

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FromTotalDays(Int64)

Find a date given the number of days from the start of the epoch.

Declaration

public static DateOnly FromTotalDays(long days)

Parameters

Type	Name	Description
System.Int64	days	The number of days.

Returns

Type	Description
DateOnly	The resulting date.

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FromTotalYears(Double)

Find the date given the number of years since the start of the epoch.

Declaration

public static DateOnly FromTotalYears(double years)

Parameters

Type	Name	Description
System.Double	years	The number of years. May include a fractional part.

Returns

Type	Description
DateOnly	The resulting date.

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GetChristmas(Int32)

Get the date of Christmas Day in the given year.

Declaration

public static DateOnly GetChristmas(int year)

Parameters

Type	Name	Description
System.Int32	year	The year.

Returns

Type	Description
DateOnly	The date of Christmas in the given year.

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GetEaster(Int32)

Get the date of Easter Sunday in the given year. Formula is from Wikipedia. This method uses the "Meeus/Jones/Butcher" algorithm from 1876, with the New Scientist modifications from 1961. Tested for years 1600..2299.

Declaration

public static DateOnly GetEaster(int year)

Parameters

Type	Name	Description
System.Int32	year	The Gregorian year number.

Returns

Type	Description
DateOnly	The date of Easter Sunday for the given year.

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GetNthWeekdayInMonth(Int32, Int32, Int32, DayOfWeek)

Find the nth weekday in a given month. Example:

// Get the 4th Thursday in January, 2023.
DateOnly meetup = XDateOnly.GetNthWeekdayInMonth(2023, 1, 4, DayOfWeek.Thursday);

A negative value for n means count from the end of the month. n = -1 means the last one in the month. n = -2 means the second-last, etc. Example:

// Get the last Monday in November, 2025.
DateOnly meetup = XDateOnly.GetNthWeekdayInMonth(2025, 11, -1, DayOfWeek.Monday);

Declaration

public static DateOnly GetNthWeekdayInMonth(int year, int month, int n, DayOfWeek dayOfWeek)

Parameters

Type	Name	Description
System.Int32	year	The year.
System.Int32	month	The month.
System.Int32	n	Which occurence of the day of the week within the month.
DayOfWeek	dayOfWeek	The day of the week.

Returns

Type	Description
DateOnly	The requested date.

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GetThanksgiving(Int32, String)

Find the date of Thanksgiving for a specified country in a given year. Only years with a holiday called "Thanksgiving" are supported. The default is "US".

Declaration

public static DateOnly GetThanksgiving(int year, string countryCode = "US")

Parameters

Type	Name	Description
System.Int32	year	The year.
System.String	countryCode	The ISO 2-letter country code.

Returns

Type	Description
DateOnly	The date of Thanksgiving.

Exceptions

Type	Condition
ArgumentInvalidException	Either this country doesn't celebrate Thanksgiving, or the method doesn't support it.

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GetTicks(DateOnly)

Get the number of ticks between the start of the epoch (0001-01-01 00:00:00) and the start of the date.

If extension properties are added to the language I may change this to a property "Ticks" later, for consistency with DateTime.

Declaration

public static long GetTicks(this DateOnly date)

Parameters

Type	Name	Description
DateOnly	date	The DateOnly instance.

Returns

Type	Description
System.Int64	The number of ticks.

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GetTotalDays(DateOnly)

Get the number of days between the start of the epoch and the given date.

Declaration

public static long GetTotalDays(this DateOnly date)

Parameters

Type	Name	Description
DateOnly	date	The DateOnly instance.

Returns

Type	Description
System.Int64	The number of days since the epoch start.

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GetTotalSeconds(DateOnly)

Get the number of seconds between the start of the epoch and the start of the date.

Declaration

public static long GetTotalSeconds(this DateOnly date)

Parameters

Type	Name	Description
DateOnly	date	The DateOnly instance.

Returns

Type	Description
System.Int64	The number of seconds since the epoch start.

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GetTotalYears(DateOnly)

Get the number of years between the start of the epoch and the start of the date.

The result will be greater than or equal to date.Year - 1 and less than date.Year.

Declaration

public static double GetTotalYears(this DateOnly date)

Parameters

Type	Name	Description
DateOnly	date	The DateOnly instance.

Returns

Type	Description
System.Double	The number of years since the epoch start.

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Subtract(DateOnly, DateOnly)

Returns the difference between two dates as a number of days. Emulates the method.

If the end date is later than the start date, the result will be positive. If they are equal, the result will be zero. Otherwise, the result will be negative.

Declaration

public static long Subtract(this DateOnly end, DateOnly start)

Parameters

Type	Name	Description
DateOnly	end	The end date.
DateOnly	start	The start date.

Returns

Type	Description
System.Int64	The number of days difference between the two dates.

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ToDateTime(DateOnly)

Convert a DateOnly to a DateTime, with default time 00:00:00.

Declaration

public static DateTime ToDateTime(this DateOnly date)

Parameters

Type	Name	Description
DateOnly	date	The DateOnly instance.

Returns

Type	Description
DateTime	The new DateTime object

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ToDateTime(DateOnly, DateTimeKind)

Convert a DateOnly to a DateTime, with default time 00:00:00 and specified DateTimeKind.

Declaration

public static DateTime ToDateTime(this DateOnly date, DateTimeKind kind)

Parameters

Type	Name	Description
DateOnly	date	The DateOnly instance.
DateTimeKind	kind	The DateTimeKind.

Returns

Type	Description
DateTime	The new DateTime object

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ToIsoString(DateOnly)

Format the date using ISO 8601 format YYYY-MM-DD. https://en.wikipedia.org/wiki/ISO_8601#Calendar_dates

Declaration

public static string ToIsoString(this DateOnly date)

Parameters

Type	Name	Description
DateOnly	date	The DateOnly instance.

Returns

Type	Description
System.String	A string representing the date in ISO format.

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ToJulianDay(DateOnly)

Convert a DateOnly object to a Julian Day value. The result gives the Julian Day at the start of the given date (00:00:00, i.e. midnight), which will always have a fraction of 0.5, since a Julian Day starts at 12:00:00 (noon). ToJulianDay(DateTime)

Declaration

public static double ToJulianDay(this DateOnly date)

Parameters

Type	Name	Description
DateOnly	date	The DateOnly instance.

Returns

Type	Description
System.Double	The Julian Day value.

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