How is the ___init() method generated and called for the interceptors?

1. Magento\Framework\Interception\Code\Generator\Interceptor::_getDefaultConstructorDefinition()

Magento 2.2.0

Magento 2.0.0

2. Magento\Framework\Interception\Interceptor::___init()

Magento 2.2.0

Magento 2.0.0