Is it bad practice, or likely to suffer performance issues, to store circular dependencies in objects?

Question

Is it bad practice or have a significant performance impact to have a cyclical reference? e.g., add object A as property of object B and then Object B as property of Object A?

An example:

<?php 

class Object_A {

    public function __construct() {
        $this->b = new Object_B( $this );       
    }

    public function get_b() {
        return $this->b;
    }

}

class Object_B {

    public function __construct( Object_A $a ) {
        $this->a = $a;
    }
}

This answer seems to be similar, but for C#.

It isn't always possible to avoid it, but causes enough problems that you should try to avoid it if at all possible — Mark Baker, Aug 24 '15 at 13:22
This is certainly a design smell. I cannot think of an example where this would be necessary, but it seems that you have. Are you just curious? If this is real work, ask your colleagues. I would try to avoid this if at all possible. — Mawg says reinstate Monica, Aug 24 '15 at 13:31

score 3 · Answer 1 · edited Apr 12 '17 at 07:31

For a more general discussion about cyclic references see What's wrong with circular references? on the programmers stackexchange site. But keep in mind the question explicitly states

I am not asking about homogenous circular references, like those in a doubly-linked list or pointer-to-parent.

PHP implements a garbage collector fully capable of collecting cycles since version 5.3.

Performance considerations are discussed under Garbage Collection - Performance Considerations in the manual.

Is it bad practice, or likely to suffer performance issues, to store circular dependencies in objects?

1 Answers1