编译器优化结构或类定义(Compiler optimization of structure or class definitions)

编译器优化对定义Common Lisp结构（或类）的影响是什么（如(defstruct person (age nil :type (or null integer))) vs (defstruct person (age -1 :type integer)) ？ 我经常发现，使用第一种形式，使用表示特殊条件的空值非常方便; 例如，如果一个人的年龄不知道。 但在第二种形式中，您还可以使用ad-hoc指定的整数（如-1）来指示此情况。 一个表示优于另一个表示是否存在优势/劣势？ （ps：在这种情况下，差异可能可以忽略不计，但似乎可能不适用于涉及哈希表等复杂对象的嵌套结构）

What is the potential impact on compiler optimization to defining a Common Lisp structure (or class) like (defstruct person (age nil :type (or null integer))) vs (defstruct person (age -1 :type integer))? I often find it convenient, using the first form, to have a null value signifying a special condition; for example, if a person's age is not known. But in the second form, you could also use an ad-hoc designated integer like -1 to indicate this condition. Is there an advantage/disadvantage to one representation over the other? (ps: In this case the difference is likely negligible, but seems like it might not be for nested structures involving complex objects like hash-tables, etc.)