Detailed explanation of PHP new static and new self

Use self:: or __CLASS__ to make a static reference to the current class, depending on the class in which the current method is defined: using static:: is no longer parsed to the class in which the current method is defined, but is calculated at actual runtime. . It can also be called "static binding" because it can be used for (but is not limited to) calls to static methods.

I was recently asked a small question in the comments of a video: Are there any special considerations when choosing to use static instead of self here? Or we can change the question like this:

What are the specific new static and new self of PHP?

In fact, it should be very clear if we look at an example:

class Father {

 public static function getSelf() {
  return new self();
 }

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

class Son extends Father {}

echo get_class(Son::getSelf()); // Father
echo get_class(Son::getStatic()); // Son
echo get_class(Father::getSelf()); // Father
echo get_class(Father::getStatic()); // Father

Pay attention to this line hereget_class(Son::getStatic()); The class Son is returned, which can be summarized as follows:

new self

1.self returns the class where the keyword new in new self is located, such as Here's an example:

public static function getSelf() {
  return new self(); // new 关键字在 Father 这里
 }

always returns Father.

new static

2.static Based on the above, it is a little smarter: static will return to execute new static( ) class, such as Son execute get_class(Son::getStatic()) returns Son, Father execute get_class(Father::getStatic()) returns Father

and in the absence of inheritance, it can be considered that new self and new static returns the same result.

Tips: You can use a good IDE to read comments directly. For example, PhpStorm:

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