public protocol TestProtocol {
    var str1: String { get }
}

@dynamicMemberLookup
open class BaseClass<ProtocolType> {
    
    public let proto: ProtocolType
    
    init(proto: ProtocolType) {
        self.proto = proto
    }
    
    public subscript<T>(dynamicMember keyPath: KeyPath<ProtocolType, T>) -> T {
        return proto[keyPath: keyPath]
    }
}

public final class TestClass: BaseClass<TestProtocol> {
    func test() {
        print(self.proto.str1) // compiles
        print(proto.str1)      // compiles
        print(self.str1)       // compiles
        print(str1)            // ERROR: Use of unresolved identifier 'str1'
    }
}