Question

I have a base class of FileCopier that is composed with two “has-a” associations to Resource Source and Resource Destination.

After construction, three properties exist in FileCopier:

- Source (instance of Resource)
- Destination (instance of Resource)
- Config (array of configuration stuff for this FileCopier)

All of the examples I find on this issue are regarding children by extension rather than children by composition.

My question is: is there any way for the Resource instance to access it’s parent’s “Config”?

Or, must I pass a reference to the parent to it’s associated children, say, via the constructor?

Answer 1

If I understand well you have:

class FileCopier{
    /* @var Source */
    private $source;

    /* @var Destination */
    private $destination;

    /* @var Config */
    private $conf;

    ...

}

And you want to access $conf from $source and $destination?
There is no parent or other magic word to access this $conf from the two other variables.
Your best bet would be to add a function to Resource which will set a local reference to Config:

class Resource {
    /* @var Config */
    protected $config;
    ...
    function setConfig(Config $config) {
        $this->config = $config;
    }
    ...
}

Or if config is set at some other point r could change or if for whatever other reason you want to access the latest $conf from your resources you can pass a ref to FileCopier instead:

class Resource {
    /* @var FileCopier */
    protected $copier;
    ...
    function setFileCopier(FileCopier $copier) {
        $this->copier = $copier;
        // and access to $this->copier->conf through a getter
        // or make $conf public in FileCopier
    }
    ...
}

Then all you have to do is to call your setter before using $source and $destination. Probably in the FileCopier:

class FileCopier{
    ...
    //first case :
    function setConfig($config) {
        $this->config = $config;
        $this->source->setConfig($config);
        $this->destination->setConfig($config);
    }

    // Or for the second case:
    function setup() {
        $this->source = new Source();
        $this->source->setFileCopier($this);

        $this->destination = new Destination();
        $this->destination->setFileCopier($this);
    }

    ...

}

Hope this helps.