假设我有两个记录:人和动物.每条记录都在一个单独的包中. 套餐人员: with animals;use animals;package persons is type person is record ... animalref: animalPOINTER; ... end record; type personPOINTER is access pe
套餐人员:
with animals; use animals; package persons is type person is record ... animalref: animalPOINTER; ... end record; type personPOINTER is access person; end persons;
包装动物:
with persons; use persons; package animals is type animal is record ... ownerref: personPOINTER; ... end record; type animalPOINTER is access animal; end animals;
我在这里有循环单元依赖,编译器会产生致命错误.
有没有人有解决这个问题的模式?
谢谢!
你需要限制,这是为了解决这个问题而引入的.见 Rationale for Ada 2005, section 4.2.动物和人是对称的(我的编辑器调整了布局和外壳;我为每个添加了一个记录组件,因此下面的演示程序可以打印一些东西):
limited with Animals; package Persons is -- One of the few things you can do with an incomplete type, which -- is what Animals.Animal is in the limited view of Animals, is to -- declare an access to it. type AnimalPOINTER is access Animals.Animal; type Person is record Name : Character; Animalref : AnimalPOINTER; end record; end Persons; limited with Persons; package Animals is type PersonPOINTER is access Persons.Person; type Animal is record Name : Character; Ownerref : PersonPOINTER; end record; end Animals;
演示程序可以全面了解动物和人物.这个例子非常笨拙;您可以通过向动物和人物添加子程序来更好地组织事物.请注意,动物的身体可以(并且必须)与人类;如果需要在人物中使用任何东西.
with Ada.Text_IO; use Ada.Text_IO; with Animals; with Persons; procedure Animals_And_Persons is A : Persons.animalPOINTER := new Animals.Animal; P : Animals.PersonPOINTER := new Persons.Person; begin A.all := (Name => 'a', Ownerref => P); P.all := (Name => 'p', Animalref => A); Put_Line (P.Name & " owns " & P.Animalref.Name); Put_Line (A.Name & " is owned by " & A.Ownerref.Name); end Animals_And_Persons;
在编译和运行时给出
$./animals_and_persons p owns a a is owned by p