Question

Can someone explain to me what the difference between

include_once 'classb.php'
class A
{
     $a = new B
}

and

class A extends B
{
     $a = new B
}

is?

What advantages/disadvantages are there to extending a class vs. including the .php file?

Answer 1

Your include_once reads in a source file, which in this case presumably has a class definition for B in it. Your extends sets up class A as inheriting class B, i.e. A gets everything in B and can then define its own modifications to that basic structure. There isn’t really any relationship at all between the two operations, and your $a = new B operations are nonsensical (not to mention syntax errors).