ObjectAssigmentError

[DavidM]

Trying to compile this but I get an ObjectAssigmentError when the items array 
is assigned.

I want to use B and C for common behavior. What am I doing wrong?
    
    
    type
      A = object of RootObj
        name: string
      B = object of A
        value: string
      C = object of A
        key: int
    
    let items : seq[A] = @[
      B(name:"Test", value:"Value"),
      C(name:"Test", key:100)
    ];