Oh the shame: my date objects weren't actually differing by more than one day because I'm an idiot and assumed that my inputs were what I thought they were! Thanks commenters for forcing me to go back and look at exactly what was in the objects. I leave this here as a memorial, or it can be reaped.

This is a bug in an application I'm working on.

The code creates two DateTime objects and subtracts one from the other to get a DateTime::Duration object.

However the DateTime::Duration object can't return a difference in number of days, which is what I need.

This is actually expected behaviour:

my $dur = DateTime::Duration->new( years => 1, months => 15 );
 
$dur->in_units('years');                # 2
$dur->in_units('months');               # 27
$dur->in_units( 'years', 'months' );    # (2, 3)
$dur->in_units( 'weeks', 'days' );      # (0, 0) !

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The last example demonstrates that there will not be any conversion between units which don't have a fixed conversion rate.

I guess my question is, how do I get the difference in days between two DateTime objects?

Updated: The current code just does 

my $diff = $dt1 - $dt2;

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Where both DateTime objects are specific fixed dates, like one is January 1, 2021 at 10 AM and the other is today at 11 AM. Surely there's a 'fixed conversion rate' in days between those? Note: They were essentially the same day!

I can understand that if I create a duration object with years => 1, months => 15 that's not something where we can be sure of the number of days, but that's not what's happening in my code.

In reply to I can't subtract one DateTime object from another to get a DateTime::Duration in days by Cody Fendant

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