protocol and associated type test

ProtocolTest.swift

//: Playground - noun: a place where people can play

import UIKit

protocol A
{
    associatedtype SomeType
    var a : SomeType { get }
}

protocol B : A
{
    typealias SomeType = String
    var a : String { get }
}

class C
{
// if uncommented, then it works. But we have a heavy dependency on `class AA`
//     var ivar : AA? = nil
    
    var ivar : B? = nil
}


class AA : A
{
    var a: String = "hello"
}

var aa = AA()
var cc = C()

cc.ivar = aa


if let cIvar = cc.ivar
{
    print(cIvar.a)
}

Version 1

Playground execution failed: error: ProtocolTest.playground:24:11: error: cannot assign value of type 'AA' to type 'B?'
cc.ivar = aa
          ^~

error: ProtocolTest.playground:26:10: error: value of type 'B?' has no member 'a'
print(cc.ivar.a)
      ~~~^~~~ ~

Version 3

Playground execution failed: error: ProtocolTest.playground:13:16: error: protocol 'B' can only be used as a generic constraint because it has Self or associated type requirements
    var ivar : B? = nil
               ^

error: ProtocolTest.playground:25:11: error: cannot assign value of type 'AA' to type 'B?'
cc.ivar = aa
          ^~

error: ProtocolTest.playground:27:10: error: value of optional type 'B?' not unwrapped; did you mean to use '!' or '?'?
print(cc.ivar.a)
         ^
             ?

protocol A {
    associatedtype SomeType
    var a : SomeType { get }
}

class B<ResolutionType> : A {
    var a: ResolutionType? = nil
}

class C {
    var ivar : B<String>? = nil
}

class AA : B<String>
{
    override init() {
        super.init()
        a = "Hello"
    }
}

var aa = AA()
var cc = C()

cc.ivar = aa

print(cc.ivar?.a)

Made the thing compile but no classes can be injected.

// if uncommented, then it works. But we have a heavy dependency on `class AA`
//     var ivar : AA? = nil

class AA : B<String>

AA must be a sub-class of A since they belong to a third-party library in my case. And I can't change the hierarchy, I'm afraid.
P.S. They are Store class and Store protocol of the ReSwift library