NAME

DateTime::SpanSet - set of DateTime spans

SYNOPSIS

$spanset = DateTime::SpanSet->from_spans( spans => [ $dt_span, $dt_span ] );

$set = $spanset->union( $set2 );         # like "OR", "insert", "both"
$set = $spanset->complement( $set2 );    # like "delete", "remove"
$set = $spanset->intersection( $set2 );  # like "AND", "while"
$set = $spanset->complement;             # like "NOT", "negate", "invert"

if ( $spanset->intersects( $set2 ) ) { ...  # like "touches", "interferes"
if ( $spanset->contains( $set2 ) ) { ...    # like "is-fully-inside"

# data extraction 
$date = $spanset->min;           # first date of the set
$date = $spanset->max;           # last date of the set

$iter = $spanset->iterator;
while ( $dt = $iter->next ) {
    # $dt is a DateTime::Span
    print $dt->start->ymd;   # first date of span
    print $dt->end->ymd;     # last date of span
};

DESCRIPTION

DateTime::SpanSet is a class that represents sets of datetime spans. An example would be a recurring meeting that occurs from 13:00-15:00 every Friday.

This is different from a DateTime::Set, which is made of individual datetime points as opposed to ranges.

METHODS

from_spans

Creates a new span set from one or more DateTime::Span objects.
```
$spanset = DateTime::SpanSet->from_spans( spans => [ $dt_span ] );
```
from_set_and_duration

Creates a new span set from one or more DateTime::Set objects and a duration.

The duration can be a DateTime::Duration object, or the parameters to create a new DateTime::Duration object, such as "days", "months", etc.
```
$spanset =
    DateTime::SpanSet->from_set_and_duration
        ( set => $dt_set, days => 1 );
```
from_sets

Creates a new span set from two DateTime::Set objects.

One set defines the starting dates, and the other defines the end dates.
```
$spanset =
    DateTime::SpanSet->from_sets
        ( start_set => $dt_set1, end_set => $dt_set2 );
```
The spans have the starting date closed, and the end date open, like in [$dt1, $dt2).

If an end date comes without a starting date before it, then it defines a span like (-inf, $dt).

If a starting date comes without an end date after it, then it defines a span like [$dt, inf).
empty_set

Creates a new empty set.
is_empty_set

Returns true is the set is empty; false otherwise.
```
print "nothing" if $set->is_empty_set;
```
clone

This object method returns a replica of the given object.
set_time_zone( $tz )

This method accepts either a time zone object or a string that can be passed as the "name" parameter to DateTime::TimeZone->new(). If the new time zone's offset is different from the old time zone, then the local time is adjusted accordingly.

If the old time zone was a floating time zone, then no adjustments to the local time are made, except to account for leap seconds. If the new time zone is floating, then the UTC time is adjusted in order to leave the local time untouched.
start, min
end, max

First or last dates in the set.

It is possible that the return value from these methods may be a DateTime::Infinite::Future or a DateTime::Infinite::Past object.

If the set ends before a date $dt, it returns $dt. Note that in this case $dt is not a set element - but it is a set boundary.

These methods may return undef if the set is empty.

These methods return just a copy of the actual boundary value. If you modify the result, the set will not be modified.
duration

The total size of the set, as a DateTime::Duration object.

The duration may be infinite.

Also available as size().
span

The total span of the set, as a DateTime::Span object.
next
```
my $span = $set->next( $dt );
```
This method is used to find the next span in the set, after a given datetime or span.

The return value is a DateTime::Span, or undef if there is no matching span in the set.
previous
```
my $span = $set->previous( $dt );
```
This method is used to find the previous span in the set, before a given datetime or span.

The return value is a DateTime::Span, or undef if there is no matching span in the set.
current
```
my $span = $set->current( $dt );
```
This method is used to find the "current" span in the set, that intersects a given datetime or span. If no current span is found, then the "previous" span is returned.

The return value is a DateTime::SpanSet, or undef if there is no matching span in the set.

If a span parameter is given, it may happen that "current" returns more than one span.

See also: intersected_spans() method.
closest
```
my $span = $set->closest( $dt );
```
This method is used to find the "closest" span in the set, given a datetime or span.

The return value is a DateTime::SpanSet, or undef if the set is empty.

If a span parameter is given, it may happen that "closest" returns more than one span.
as_list

Returns a list of DateTime::Span objects.
```
my @dt_span = $set->as_list( span => $span );
```
Just as with the iterator() method, the as_list() method can be limited by a span.

Applying as_list() to a large recurring spanset is a very expensive operation, both in CPU time and in the memory used.

For this reason, when as_list() operates on large recurrence sets, it will return at most approximately 200 spans. For larger sets, and for infinite sets, as_list() will return undef.

Please note that this is explicitly not an empty list, since an empty list is a valid return value for empty sets!

If you really need to extract spans from a large set, you can:

- limit the set with a shorter span:
```
my @short_list = $large_set->as_list( span => $short_span );
```
- use an iterator:
```
my @large_list;
my $iter = $large_set->iterator;
push @large_list, $dt while $dt = $iter->next;
```
union
intersection

complement

Set operations may be performed not only with DateTime::SpanSet objects, but also with DateTime, DateTime::Set and DateTime::Span objects. These set operations always return a DateTime::SpanSet object.

$set = $spanset->union( $set2 );         # like "OR", "insert", "both"
$set = $spanset->complement( $set2 );    # like "delete", "remove"
$set = $spanset->intersection( $set2 );  # like "AND", "while"
$set = $spanset->complement;             # like "NOT", "negate", "invert"

intersected_spans

This method can accept a DateTime list, a DateTime::Set, a DateTime::Span, or a DateTime::SpanSet object as an argument.
```
$set = $set1->intersected_spans( $set2 );
```
The method always returns a DateTime::SpanSet object, containing all spans that are intersected by the given set.

Unlike the intersection method, the spans are not modified. See diagram below:
```
             set1   [....]   [....]   [....]   [....]
             set2      [................]

     intersection      [.]   [....]   [.]

intersected_spans   [....]   [....]   [....]
```
intersects
contains

These set functions return a boolean value.
```
if ( $spanset->intersects( $set2 ) ) { ...  # like "touches", "interferes"
if ( $spanset->contains( $dt ) ) { ...    # like "is-fully-inside"
```
These methods can accept a DateTime, DateTime::Set, DateTime::Span, or DateTime::SpanSet object as an argument.

intersects() returns 1 for true, and 0 for false. In a few cases the algorithm can't decide if the sets intersect at all, and intersects() will return undef.
iterator / next / previous

This method can be used to iterate over the spans in a set.
```
$iter = $spanset->iterator;
while ( $dt = $iter->next ) {
    # $dt is a DateTime::Span
    print $dt->min->ymd;   # first date of span
    print $dt->max->ymd;   # last date of span
}
```
The boundaries of the iterator can be limited by passing it a span parameter. This should be a DateTime::Span object which delimits the iterator's boundaries. Optionally, instead of passing an object, you can pass any parameters that would work for one of the DateTime::Span class's constructors, and an object will be created for you.

Obviously, if the span you specify does is not restricted both at the start and end, then your iterator may iterate forever, depending on the nature of your set. User beware!

The next() or previous() methods will return undef when there are no more spans in the iterator.
start_set
end_set

These methods do the inverse of the from_sets method:

start_set retrieves a DateTime::Set with the start datetime of each span.

end_set retrieves a DateTime::Set with the end datetime of each span.
map ( sub { ... } )
```
# example: enlarge the spans
$set = $set2->map( 
    sub {
        my $start = $_->start;
        my $end = $_->end;
        return DateTime::Span->from_datetimes(
            start => $start,
            before => $end,
        );
    }
);
```
This method is the "set" version of Perl "map".

It evaluates a subroutine for each element of the set (locally setting "$_" to each DateTime::Span) and returns the set composed of the results of each such evaluation.

Like Perl "map", each element of the set may produce zero, one, or more elements in the returned value.

Unlike Perl "map", changing "$_" does not change the original set. This means that calling map in void context has no effect.

The callback subroutine may not be called immediately. Don't count on subroutine side-effects. For example, a print inside the subroutine may happen later than you expect.

The callback return value is expected to be within the span of the previous and the next element in the original set.

For example: given the set [ 2001, 2010, 2015 ], the callback result for the value 2010 is expected to be within the span [ 2001 .. 2015 ].
grep ( sub { ... } )
```
# example: filter out all spans happening today
my $today = DateTime->today;
$set = $set2->grep( 
    sub {
        return ( ! $_->contains( $today ) );
    }
);
```
This method is the "set" version of Perl "grep".

It evaluates a subroutine for each element of the set (locally setting "$_" to each DateTime::Span) and returns the set consisting of those elements for which the expression evaluated to true.

Unlike Perl "grep", changing "$_" does not change the original set. This means that calling grep in void context has no effect.

Changing "$_" does change the resulting set.

The callback subroutine may not be called immediately. Don't count on subroutine side-effects. For example, a print inside the subroutine may happen later than you expect.
iterate

Internal method - use "map" or "grep" instead.

This function apply a callback subroutine to all elements of a set and returns the resulting set.

The parameter $_[0] to the callback subroutine is a DateTime::Span object.

If the callback returns undef, the datetime is removed from the set:
```
sub remove_sundays {
    $_[0] unless $_[0]->start->day_of_week == 7;
}
```
The callback return value is expected to be within the span of the previous and the next element in the original set.

For example: given the set [ 2001, 2010, 2015 ], the callback result for the value 2010 is expected to be within the span [ 2001 .. 2015 ].

The callback subroutine may not be called immediately. Don't count on subroutine side-effects. For example, a print inside the subroutine may happen later than you expect.

SUPPORT

Support is offered through the datetime@perl.org mailing list.

Please report bugs using rt.cpan.org

AUTHOR

Flavio Soibelmann Glock <fglock@gmail.com>

The API was developed together with Dave Rolsky and the DateTime Community.

COPYRIGHT

The full text of the license can be found in the LICENSE file included with this module.

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