Adjusting

All objects in the dates library are immutable, but it’s still possible to ‘adjust’ them by creating new objects with a date relative to the original object, like so:

$date = Date::mktime(2014, 1, 1);
$date->addYears(1)->string("Y-m-d");    # "2015-01-01"

The above works because the string method is chained to the new object returned by addyears().
The important thing to remember is that you always need the return value of an adjustment call, doing the following is useless:

$date = Date::now();
for ($i = 0; $i < 10; $i++) {
    $date->addYears($i);
    echo $date->string("Y");
}

In the above code the $date object is never changed so will always output the current year. In order to mimic mutability you can set the $date variable to the return of the adjustment:

$date = Date::now();
for ($i = 0; $i < 10; $i++) {
    $date = $date->addYears($i);
    echo $date->string("Y");
}

Relative Dates

The following adjustment methods are available for getting relative dates:

$date->addYears($years);
$date->subYears($years);

$date->addMonths($months);
$date->subMonths($months);

$date->addWeeks($weeks);
$date->subWeeks($weeks);

$date->addDays($days);
$date->subDays($days);

Relative Times

And there are a few methods for getting relative times:

$date->addHours($hours);
$date->subHours($hours);

$date->addMinutes($minutes);
$date->subMinutes($minutes);

$date->addSeconds($seconds);
$date->subSeconds($seconds);

Relative Days

It’s common to need a specific day in the future or past, you can use getNext() and getPrevious() for this:

$nextMonday = $date->getNext(Days::MONDAY);
$lastSaturday = $date->getPrevious(Days::SATURDAY);

These methods will always get the “next” or “previous” day, they don’t include the current day, if you want to then you can do something like this:

if (!$date->isMonday()) {
    $date = $date->getNext(Days::MONDAY);
}