Analysis of the difference between new self() and new static() in PHP

This article mainly introduces the difference between new self() and new static() in PHP. It has certain reference value. Those who are interested can learn about it

1.new static() is New features introduced in PHP 5.3 version.

2. Whether it is new static() or new self(), a new object is new.

3. What is the difference between the objects produced by new from these two methods? To put it bluntly, is the object produced by new the same class instance or a different class instance?

In order to explore the above problem, let’s first write a simple code:

class Father {

 public function getNewFather() {
  return new self();
 }

 public function getNewCaller() {
  return new static();
 }

}

$f = new Father();

print get_class($f->getNewFather());
print get_class($f->getNewCaller());

Note that the get_class() method of the above code uses To get the class name to which the instance belongs.

The result here is: regardless of calling getNewFather() or getNewCaller(), an instance of the Father class is returned.

The printed result is: FatherFather

At this point, it seems that there is no difference between new self() and new static(). Let’s go on:

class Sun1 extends Father {

}

class Sun2 extends Father {

}

$sun1 = new Sun1();
$sun2 = new Sun2();

print get_class($sun1->getNewFather());
print get_class($sun1->getNewCaller());
print get_class($sun2->getNewFather());
print get_class($sun2->getNewCaller());

Look at the above code, now this Father class has two subclasses, due to the getNewFather() and getNewCaller() of the Father class is public, so subclasses inherit these two methods.

The printed result is: FatherSun1FatherSun2

We found that whether it is Sun1 or Sun2, the object returned by calling getNewFather() is an instance of the Father class, while getNewCaller() returns the call Examples of

That is, $sun1 returns an instance of the Sun1 class, and $sun2 returns an instance of the Sun2 class.

Now I seem to understand the difference between new self() and new static().

First of all, their difference can only be reflected in inheritance. If there is no inheritance, then there is no difference between the two.

Then, the instance returned by new self() is unchanged for thousands of years. No matter who calls it, it will return an instance of the same class, while new static() is determined by the caller.

The caller of $sun1->getNewCaller() above is $sun1, right! $sun1 is an instance of class Sun1, so what is returned is an instance of class Sun1. The same reason for $sun2 will not be repeated.

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