Make DateTime::createFromFormat() return child class instead of parent

问题

I'm extending DateTime do add some useful methods and constants.

When using new to create a new object everything is fine but when using the static method createFromFormat it always returns the original DateTime object and of course none of the child methods are available.

I am using the following code to circumvent this issue. Is this the best approach?

namespace NoiseLabs\DateTime;

class DateTime extends \DateTime
{
    static public function createFromFormat($format, $time)
    {
        $ext_dt = new self();

        $ext_dt->setTimestamp(parent::createFromFormat($format, time)->getTimestamp());

        return $ext_dt;
    }
}

回答1:

This is the way to go. However, since what seems you want to do is to render the DateTime class extensible, I'd suggest you use static instead of self:

namespace NoiseLabs\DateTime;

class DateTime extends \DateTime
{
    static public function createFromFormat($format, $time)
    {
        $ext_dt = new static();
        $parent_dt = parent::createFromFormat($format, $time);

        if (!$parent_dt) {
            return false;
        }

        $ext_dt->setTimestamp($parent_dt->getTimestamp());
        return $ext_dt;
    }
}

It's not necessary if you don't plan on extending the class, but if someone ever does, it will prevent him from having to do the same workaround again.

回答2:

I think your solution is fine. An alternative way (just refactored a bit) is this:

public static function fromDateTime(DateTime $foo)
{
  return new static($foo->format('Y-m-d H:i:s e')); 
}

public static function createFromFormat($f, $t, $tz)
{
  return static::fromDateTime(parent::createFromFormat($f, $t, $tz));
}

I'm not sure what the best way to implement the fromDateTime is. You could even take what you've got and put it in there. Just make sure not to lose the timezone.

Note that you could even implement __callStatic and use a bit of reflection to make it future proof.

回答3:

class DateTimeEx extends DateTime
{
    static public function createFromFormat($format, $time, $object = null)
    {
        return new static(DateTime::createFromFormat($format, $time, $object)->format(DateTime::ATOM));
    }
}

回答4:

Previous solutions neglect time zones and microseconds, so my little improve is here. I prefer variant 1, but in terms of performance 2 can be little faster on old PHPs.

class NDateTimeImmutable extends \DateTimeImmutable
{
    public static function createFromFormat1($format, $time)
    {
        $parent = parent::createFromFormat($format, $time);
        if (!$parent) {
            return false;
        }
        //Seting timezone like this and not by format to preserve timezone format
        $static = new static($parent->format('Y-m-d\TH:i:s.u'), $parent->getTimezone());
        return $static;
    }

    public static function createFromFormat2($format, $time)
    {
        $parent = parent::createFromFormat($format, $time);
         if (!$parent) {
            return false;
        }
        $serialized = serialize($parent);
        // numbers can be computed by strlen() 
        // eg. strlen(parent::class) = 17 but it is slow
        $serialized = strtr($serialized, ['17:"'.parent::class => '18:"'.static::class]);
        return unserialize($serialized);
    }
}

来源：https://stackoverflow.com/questions/5450197/make-datetimecreatefromformat-return-child-class-instead-of-parent