php static property

Question

I have two code snippets (regarding the static keyword) which I expect them to have same output, but actually the outputs are different.

The question is

Answer 1

If you pass a static variable to a subclass, then this variable is shared (it always has the same value in both classes). If you overwrite the static variable in a subclass, then its a new static variable independent of the static variable from the parent.

In Snippet 1 base::var and sub::var have different memory allocations, because you defined $var = 2; in the class sub.

In Snippet 2 base::var and sub::var have the same memory allocation, because you did not specify $var2 in the class sub2.

Thats why base:var is not changing. It would also not change if you change $var from sub class later like this:

class base
{
    public static $var = 1;
}

class sub extends base
{
    public static $var = 2;
}
sub::var = 3
echo base::var; // Outputs 1