When using DateTime::Span->intersects to check for intersections, the spans produced by DateTime::Span->from_datetime_and_duration, and those produced by DateTime::Span->from_datetimes, give what appear to be inconsistent results:

use strict;
use warnings;
use DateTime;
use DateTime::Span;
use Test::More 'no_plan';

my $dt1 = DateTime->new(
    day  =>  1, month  => 1, year   => 2011,
    hour => 12, minute => 0, second =>    0,
);

my $dt2 = $dt1->clone->add( hours => 1 );
my $duration = DateTime::Duration->new( hours => 1 );

{
    my $span = DateTime::Span->from_datetimes(
        start => $dt1,
        end   => $dt2,
    );

    diag $span->start->datetime();
    diag $span->end->datetime();

    is( $span->intersects( $dt1 ), 1,
        'Spanset intersects $dt1'
    );

    is( $span->intersects( $dt2 ), 1,
        'Span intersects $dt2'
    );

    is( DateTime::Duration->compare( $span->duration, $duration ), 0,
        'Duration is 1 hour'
    );
}

{
    my $span = DateTime::Span->from_datetime_and_duration(
        start    => $dt1,
        duration => $duration,
    );

    diag $span->start->datetime();
    diag $span->end->datetime();

    is( $span->intersects( $dt1 ), 1,
        'Span intersects $dt1'
    );

    is( $span->intersects( $dt2 ), 1,
        'Span intersects $dt2'
    );

    is( DateTime::Duration->compare( $span->duration, $duration ), 0,
        'Duration is 1 hour'
    );
}

[download]

Here are the test results:

# 2011-01-01T12:00:00
# 2011-01-01T13:00:00
ok 1 - Spanset intersects $dt1
ok 2 - Span intersects $dt2
ok 3 - Duration is 1 hour
# 2011-01-01T12:00:00
# 2011-01-01T13:00:00
ok 4 - Span intersects $dt1
not ok 5 - Span intersects $dt2
#   Failed test 'Span intersects $dt2'
#   at /home/mike/test.t line 51.
#          got: '0'
#     expected: '1'
ok 6 - Duration is 1 hour
1..6
# Looks like you failed 1 test of 6.

[download]

Note: subtracting one nanosecond from $dt2 in the failing test causes it to succeed: 

is( $span->intersects( $dt2->clone->subtract( nanoseconds => 1 ) ), 1,
    'Span intersects $dt2'
);

[download]

It therefore looks as though one nanosecond is going missing somewhere.

Is this intentional -- am I missing something to do with DateTime::Duration objects, or is this down to a bug in one of the DateTime modules?

I'm using DateTime version 0.70 and DateTime::Span version 0.30 (the latest versions at the time of writing).

Update: After quite a lot of digging, I discovered that the new end of set created by DateTime::Span->from_datetime_and_duration is open by default -- it is a semi-open set with a start and open end. The end is therefore before the time+duration (by one nanosecond). That explains why the intersection is false.

The fact that the end of the set is open is stated in the docs, but I had not understood its ramifications. I'm still not clear on why the end of the set defaults to being open, but at least I can work around the issue I had.

In reply to DateTime::Span intersection inconsistencies by mikeman

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