title: Relation between Existential Container and struct instance which conform protocol
body: <p>I'm trying to understand how to find protocol method's implementation.</p>
  <p>I know that Swift uses an Existential Container for fixed-size storage in Stack memory which manages how to describe an instance of a <code>struct</code> in memory. and it has a Value Witness Table (VWT) and Protocol Witness Table (PWT)</p>
  <p>VWTs know how to manage real value in instance of struct (their lifecycle) and PWTs know the implementation of protocol's method.</p>
  <p>But I want know the relation between the instance of a struct and the &quot;existential container&quot;.</p>
  <p>Does an instance of <code>struct</code> have a pointer which refers to an existential container?</p>
  <p>How does an instance of a <code>struct</code> know its existential container?</p>