Magento 2 – Circular Dependency: Customer Model Session and URL

The easiest way to resolve circular dependencies (though not always the best) is to use Proxies.

Proxy for a class is an auto-generated class (meaning, Magento will create it automatically if not found through auto-loader) which has a dependency on the Object Manager and has the same interface as the original class.

Implementation of any method of the Proxy is just an invocation of the same method of the original class. It does not have original class required in constructor, instead the object of the original class is created through the Object Manager the first time some method of the Proxy is invoked.

Here is an example of the Proxy from the core (\Magento\Backend\Model\Auth\Proxy):

/**
 * Get proxied instance
 *
 * @return \Magento\Backend\Model\Auth
 */
protected function _getSubject()
{
    if (!$this->_subject) {
        $this->_subject = true === $this->_isShared
            ? $this->_objectManager->get($this->_instanceName)
            : $this->_objectManager->create($this->_instanceName);
    }
    return $this->_subject;
}

/**
 * {@inheritdoc}
 */
public function setAuthStorage($storage)
{
    return $this->_getSubject()->setAuthStorage($storage);
}

To use a proxy, instead of reference to the class (anywhere in di.xml or in constructor dependency), reference the Proxy by appending the name of the class with \Proxy, i.e.:

<type name="Magento\Customer\Model\Config\Share">
<plugin name="Company_Modulename::Share" type="\Company\Modulename\Plugin\Config\Share\Proxy" sortOrder="1"/>

It is always worthwhile analyzing are there ways to rewrite the business logic to avoid circular dependencies before using Proxies (or for the same matter an Object Manager in constructor)