示例

// Construction
let years1 = RelativeDelta::with_years(1).new();
let months12 = RelativeDelta::with_months(12).new();
assert_eq!(years1, months12);

let years1 = RelativeDelta::with_years(1).and_days(32).new();
// If same parameter is specified twice, only the latest is applied.
let months6 = RelativeDelta::with_months(12).with_months(6).new();
assert_eq!(months6, RelativeDelta::with_months(6).new());
// Below is identical to: RelativeDelta::yysmmsdds(Some(2020), 1, Some(1), 3, None, 12).new();
let rddt = RelativeDelta::with_year(2020).and_years(1).and_month(Some(1)).and_months(3).and_days(12).new();

// Two or more RelativeDeltas can be added and substracted. However, note that constants are lost in the process.
let lhs = RelativeDelta::yysmmsdds(Some(2020), -4, Some(1), 3, None, 0).new();
let rhs = RelativeDelta::yysmmsdds(Some(2020), 1, Some(1), 42, None, 0).new();
assert_eq!(lhs + rhs, RelativeDelta::with_years(-3).and_months(45).new());
assert_eq!(lhs - rhs, RelativeDelta::with_years(-5).and_months(-39).new());
assert_eq!(-lhs + rhs, RelativeDelta::with_years(5).and_months(39).new());

// The RelativeDelta can be multiplied with a f64.
assert_eq!(rhs * 0.5, RelativeDelta::with_years(2).and_year(Some(2020)).and_months(3).and_month(Some(1)).new());

// This crates party piece is the ability to calculate dates based on already existing chrono::DateTime
// If one would like to get the last day of the month that one is currently in, it could be done with:
println!("{}", Utc::now() + RelativeDelta::with_day(1).and_months(1).and_days(-1).new());
// Above first sets the day of the month to the 1st, then adds a month and subtracts a day.

// One could also request the first monday after one year by
let first_monday_after_one_year = RelativeDelta::with_years(1).and_weekday(Some((Weekday::Mon, 1))).new();
let d = Utc.ymd(2020, 1, 1).and_hms(0,0,0) + first_monday_after_one_year;
assert_eq!(d, Utc.ymd(2021, 1, 4).and_hms(0,0,0));