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Question

我想从“阿达精华”（2005），适合于我的工作，实现队列管理器的例子。最小的所需的代码：

package1.ads：

with Ada.Finalization; 
    use Ada; 


     generic 
      type Element is tagged private; 
     package Lists is 
      use Ada.Finalization; 
      type Item is new Element with private; 
      type Item_Reference is access all Item'Class; 
      type Forward_List is new Controlled with private; 
      function Init return Forward_List; 
      function Is_Empty(Self:Forward_List'Class) return Boolean; 
      procedure Add(Self:in out Forward_List;I:in Item'Class); 

     private 
      type Item is new Element with null record;  
      type Forward_List is new Controlled with 
       record 
       ......... 
       end record; 
      type Forward_List_Reference is access all Forward_List; 
      overriding procedure Initialize(List:in out Forward_List); 
      overriding procedure Finalize(List:in out Forward_List); 
     end Lists; 

包体：

package body Lists is 

function Init return Forward_List is 
     FL_new:Forward_List_Reference:=new Forward_List; 
    begin 
     return FL_new.all; 
    end Init; 

    function Is_Empty(Self:Forward_List'Class) return Boolean is 
    begin 
     return Self.Count=0; 
    end Is_Empty; 


    procedure Add(Self:in out Forward_List;I:Item'Class) is 
    begin 
     null; 
    end Add; 

    procedure Finalize(Node:in out Forward_List_Node) is 
    begin 
     null; 
    end Finalize; 

    overriding procedure Initialize (List:in out Forward_List) is 
    begin 
     null; 
    end Initialize; 

    overriding procedure Finalize (List:in out Forward_List) is 
    begin   
     null; 
    end Finalize; 

end Lists; 

Main.adb（采用这种封装）：

with Lists; 
with GNAT.Strings; 
with Ada.Finalization;use Ada.Finalization; 
procedure main is 
    use GNAT.Strings; 
    type Temp is new Controlled with 
     record 
     Name:Integer; 
     end record; 
    package Temp_List is new Lists(Temp); 
    FL:Temp_List.Forward_List:=Temp_List.Init; 

    Instance:Temp:=Temp'(Controlled with 
         Name => 60); 
begin 
    Temp_List.Add(Self => FL, 
       I => Instance); 
end main; 

结果：

Builder results 
E:\ADA\test_containers\20160303\main.adb 
15:11 expected an access type with designated type "Item'class" defined at lists.ads:10, instance at line 9 
found type "Temp" 

我想整个星期都解决这个问题，阅读有关这方面的文献（包，标记记录，类范围类型和泛型），并不能理解问题。

为了让这段代码的工作我修改（由元素替换Item'Class）封装规格文件： package2.ads：

with Ada.Finalization; 
    use Ada; 

    generic 
     type Element is private; 
    package Lists is 
     use Ada.Finalization; 
     type Forward_List is new Controlled with private; 
     function Init return Forward_List; 
     function Is_Empty(Self:Forward_List'Class) return Boolean; 
     procedure Add(Self:in out Forward_List;I:in Element); 

    private 
     type E_Reference is access all Element; 
     type Forward_List is new Controlled with 
      record 
      ......... 
      end record; 
     type Forward_List_Reference is access all Forward_List; 
     overriding procedure Initialize(List:in out Forward_List); 
     overriding procedure Finalize(List:in out Forward_List); 
    end Lists; 

然后代码 “main.adb” 开头良好。

所以这是我的问题：我怎么能与第一规格（例如，从“阿达精华”（包1））工作？

Answer 1

西蒙·怀特提供了注释的答案：

我张贴在comp.lang.ada这个问题，普遍的看法是，这本书是错误的。

我会继续我的工作与方法中的元素（根据我的问题package2）。