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# `std.datetime.interval.Interval.shift` - multiple declarations

## Function Interval.shift

Shifts the interval forward or backwards in time by the given duration (a positive duration shifts the interval forward; a negative duration shifts it backward). Effectively, it does `begin += duration` and `end += duration`.

``` void shift(D) (   D duration ) pure if (__traits(compiles, begin + duration)); ```

### Parameters

NameDescription
duration The duration to shift the interval by.

### Throws

`DateTimeException` this interval is empty or if the resulting interval would be invalid.

### Example

``````auto interval1 = Interval!Date(Date(1996, 1, 2), Date(2012, 4, 5));
auto interval2 = Interval!Date(Date(1996, 1, 2), Date(2012, 4, 5));

interval1.shift(dur!"days"(50));
assert(interval1 == Interval!Date(Date(1996, 2, 21), Date(2012, 5, 25)));

interval2.shift(dur!"days"(-50));
assert(interval2 == Interval!Date(Date(1995, 11, 13), Date(2012, 2, 15)));``````

## Function Interval.shift

Shifts the interval forward or backwards in time by the given number of years and/or months (a positive number of years and months shifts the interval forward; a negative number shifts it backward). It adds the years the given years and months to both begin and end. It effectively calls `add!"years"()` and then `add!"months"()` on begin and end with the given number of years and months.

``` void shift(T) (   T years,   T months = 0,   AllowDayOverflow allowOverflow = AllowDayOverflow.yes ) if (isIntegral!T); ```

### Parameters

NameDescription
years The number of years to shift the interval by.
months The number of months to shift the interval by.
allowOverflow Whether the days should be allowed to overflow on `begin` and `end`, causing their month to increment.

### Throws

`DateTimeException` if this interval is empty or if the resulting interval would be invalid.

### Example

``````auto interval1 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));
auto interval2 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));

interval1.shift(2);
assert(interval1 == Interval!Date(Date(1998, 1, 2), Date(2014, 3, 1)));

interval2.shift(-2);
assert(interval2 == Interval!Date(Date(1994, 1, 2), Date(2010, 3, 1)));``````