Question

我想实现“Ada Distilled”（2005）的队列管理器示例，以适应我的工作。最少的代码：

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（使用此包）：

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"

我想整个星期解决这个问题，阅读有关此问题的文献（包，标记记录，类范围类型和泛型），并且无法理解这个问题。

为了使这段代码工作，我修改了（将Element'Class by Element替换）包规范文件： 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”开始很好。

这就是我的问题：我如何使用第一个规范（例如“Ada Distilled”（package1））？

Answer 1

Simon Wright在评论中提供了答案：

我在comp.lang.ada上发布了这个问题，一般认为这本书是错误的。

我将继续使用Element in methods（根据我的问题中的package2）。

包含通用标记的包

1 个答案: