Are PHP DateInterval comparable like DateTime?

Question

I discovered that a DateTime object in PHP can be compared to another as the \">\" and \"<\" operators are overloaded.

Is it the same with DateInterval?

A

Answer 1

EDIT:

class ComparableDateInterval extends DateInterval
{
    /** 
     * Leap-year safe comparison of DateInterval objects.
     */
    public function compare(DateInterval $oDateInterval)
    {   
        $fakeStartDate1 = date_create();
        $fakeStartDate2 = clone $fakeStartDate1;
        $fakeEndDate1   = $fakeStartDate1->add($this);
        $fakeEndDate2   = $fakeStartDate2->add($oDateInterval);

        if($fakeEndDate1 < $fakeEndDate2) {
            return -1; 
        } elseif($fakeEndDate1 == $fakeEndDate2) {
            return 0;
        }   
        return 1;
    }   
}

$int15 = new ComparableDateInterval('P15D');
$int20 = new ComparableDateInterval('P20D');

var_dump($int15->compare($int20) == -1); // should be true;

See @fyrye's answer for the rationale (and upvote it!). My original answer did not deal with leap years safely.

---

Original Answer

While I upvoted this question, I downvoted the accepted answer. That's because it didn't work for me on any of my PHP installations and because fundamentally it's hinging on something broken internally.

What I did instead is migrate the aforementioned patch which never made it into trunk. FWIW I checked a recent release, PHP 5.6.5, and the patch still isn't there. The code was trivial to port. The only thing is a warning in how it makes the comparison

If $this->days has been calculated, we know it's accurate, so we'll use that. If not, we need to make an assumption about month and year length, which isn't necessarily a good idea. I've defined months as 30 days and years as 365 days completely out of thin air, since I don't have the ISO 8601 spec available to check if there's a standard assumption, but we may in fact want to error out if we don't have $this->days available.

Here's an example. Note, if you need to compare a DateInterval that was returned from some other call, you'll have to create a ComparableDateInterval from it first, if you want to use it as the source of the comparison.

$int15 = new ComparableDateInterval('P15D');
$int20 = new ComparableDateInterval('P20D');

var_dump($int15->compare($int20) == -1); // should be true;

Here's the code

/**
 * The stock DateInterval never got the patch to compare.
 * Let's reimplement the patch in userspace.
 * See the original patch at http://www.adamharvey.name/patches/DateInterval-comparators.patch
 */
class ComparableDateInterval extends DateInterval
{
    static public function create(DateInterval $oDateInterval)
    {
        $oDi         = new ComparableDateInterval('P1D');
        $oDi->s      = $oDateInterval->s;
        $oDi->i      = $oDateInterval->i;
        $oDi->h      = $oDateInterval->h;
        $oDi->days   = $oDateInterval->days;
        $oDi->d      = $oDateInterval->d;
        $oDi->m      = $oDateInterval->m;
        $oDi->y      = $oDateInterval->y;
        $oDi->invert = $oDateInterval->invert;

        return $oDi;
    }

    public function compare(DateInterval $oDateInterval)
    {
        $oMyTotalSeconds   = $this->getTotalSeconds();
        $oYourTotalSeconds = $oDateInterval->getTotalSeconds();

        if($oMyTotalSeconds < $oYourTotalSeconds)
            return -1;
        elseif($oMyTotalSeconds == $oYourTotalSeconds)
            return 0;
        return 1;
    }

    /**
     * If $this->days has been calculated, we know it's accurate, so we'll use
     * that. If not, we need to make an assumption about month and year length,
     * which isn't necessarily a good idea. I've defined months as 30 days and
     * years as 365 days completely out of thin air, since I don't have the ISO
     * 8601 spec available to check if there's a standard assumption, but we
     * may in fact want to error out if we don't have $this->days available.
     */
    public function getTotalSeconds()
    {
        $iSeconds = $this->s + ($this->i * 60) + ($this->h * 3600);

        if($this->days > 0)
            $iSeconds += ($this->days * 86400);

        // @note Maybe you prefer to throw an Exception here per the note above
        else
            $iSeconds += ($this->d * 86400) + ($this->m * 2592000) + ($this->y * 31536000);

        if($this->invert)
            $iSeconds *= -1;

        return $iSeconds;
    }
}