“self”如何在继承的类中完全正常工作？

Question

According to php, class::self always points to the class itself, but as I wrote down these codes, something strange happens:

class C_foo{
    function foo() { return "foo() from C_foo"; }
    function bar() { echo self::foo(); }
}

class C_bar extends C_foo{
    function foo() { return "foo() from C_bar"; }
}

C_foo::bar();
C_bar::bar();

I thought the output would have been:

foo() from C_foo
foo() from C_bar

But in fact:

foo() from C_foo
foo() from C_foo

It means that the self in parent class does NOT exactly inherit into the child, it works more like to this:

foo() {return parent::foo();}

Is that a feature from php or is it a bug? Or is it mean to be like this?

Otherwise, such thing is occurred as I tried to tell a class create objects from itself, the code is something like this:

class Models {
    function find($exp) {
        ...
        ...

        $temp_model = new self();
        ...
        ...
    }
}

class Something extends Models {...}

$somethings = Something::find("...");

Maybe someone would ask, "why don't you set a variable with the value of class , and use the variable as the __construction function?"

Like this:

...
...
function find($exp) {
    ...
    ...
    $class_name = __class__;
    $temp_model = new $class_name();
    ...
    ...
}
...

In fact I did that, and got a even more weird result:

It works only when the class does not have any property or function but find() , or an error telling me a variable shows off where a function sould exist would jump out.

Answer 1

It sounds like you're describing the PHP feature known as 'late static binding'.

PHP provides two syntaxes: self:: and static:: .

static was introduced in PHP 5.3 because a lot of people expected self to work the you're describing.

See the PHP manual for more: http://php.net/manual/en/language.oop5.late-static-bindings.php

You can also use the syntax new self() or new static() to create new instances:

$parent = new self();
$child = new static();

Answer 2

This is because the class which receives the methods of the parent is of that class. So:

$bar is Bar, therefore self:: refers to Bar, not to Foo. Even though that method is from Foo.

This may be different from Java, but it probably indicates how PHP is doing inheritance internally.

Answer 3

In PHP, classes are not object. Because of that, there is no inheritance of static methods (actually, they are similar to global functions).

So, when C_foo says self, it always means C_foo (even if you called a method from C_bar).

If you want create instances from an abstract class method, you should try the Factory pattern.