PHP static delay statically binding _php tutorial

If you are a lazy programmer, you see the following code may be annoyed

Abstract class u{

}

Class U1 extends u{

public static function Create () {

return new U1 ();

}

}

Class U2 extends u{

public static function Create () {

return new U2 ();

}

}

This piece of code works fine, but a lot of repetitive code can be annoying.

I don't want to add the Create method to each subclass, and if you put the Create method in the superclass U, the code might be

Abstract class u{

public static function Create () {

return new self ();

}

}

Class U1 extends u{

function A () {}

}

Class U2 extends u{

}

U1::create ();

It looks neat and tidy, now we put common code in one place and self as a reference to that class. But here we have a hypothesis about self.

In fact, Self's role in the class is not exactly the same as $this's effect on the object. Self is not referring to the invocation context, he refers to the parsing context, so if you run the above case, you will get

Fatal Error:cannot Instantiate abstract class U in D:\wamp\www\test\oop\static.php on line 21

Self is therefore parsed to define the U of Create, rather than the U1 class that resolves to call self.

Prior to php5.3, there were strict restrictions in this area, resulting in a lot of awkward solutions, php5.3 introduced lazy static binding and the use of the keyword static

Static is similar to self, but it refers to the class being called instead of the containing class.

In the following example U1::create will generate the U1 object instead of instantiating the U object

Abstract class u{

public static function Create () {

return new static ();

}

}

Class U1 extends u{

}

Class U2 extends u{

}

U1::create ();

Static can be used not only for instantiation, but also as a call identifier for a static method, even from a non-static context, as self,parent.

Abstract class u{

Private $group;

Public Function __construct () {

$this->group=static::getgroup ();

}

public static function Create () {

return new static ();

}

static function Getgroup () {

return ' default ';

}

}

Class U1 extends u{

}

Class U2 extends u{

static function Getgroup () {

Return ' U2 ';

}

}

Class U3 extends u2{

}

Print_r (U1::create ());

Echo '
';

Print_r (U3::create ());

U1 Object ([group:u:private] = default)

U3 Object ([group:u:private] = U2)

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