∀ {α : Type u} {β : α → Type v} {m : Std.DHashMap.Raw α β} [inst : BEq α] [inst_1 : Hashable α] [inst_2 : LawfulBEq α],
  m.WF →
    ∀ {k a : α} [inst_3 : Inhabited (β a)] {v : β k},
      (m.insertIfNew k v).get! a = if h : (k == a) = true ∧ k ∉ m then cast ⋯ v else m.get! a