PROSAGA码农传奇-Ada-如何返回类广泛对象的副本，并修改了Ada中的基类型

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  <P>
    我知道它需要更多的工作，但你也可以改变Add_To使用Base而不是Base'Class。然后，您必须为具有多个空记录扩展名的任何派生类型覆盖它，但您将获得所需的静态数组结果。派生的实现类似于您实现Create的方式。
  </p>
  <P>
    示例（我修改了派生类以强制使用非空记录扩展
编译器要求您派生操作：
  </p>
   <pre class="lang-ada prettyprint-override">
    <code>
      with Ada.Text_IO; use Ada.Text_IO;
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;

procedure Hello is

package Bases is
        type Base (<>) is tagged private; -- I want to hide the size
        type Int_List is array (Positive range <>) of Integer; -- as an example

function Create return Base; -- returns an empty Base

function Add_To (This : Base; I : Integer) return Base; -- Append
        function Image (This : Base) return String; -- Dispatching example
        function List (This : Base'Class) return Int_List; -- Get the data for internal use
    private
        type Base (Size : Natural) is tagged record
            Ints : Int_List (1 .. Size);
        end record;
    end Bases;

package body Bases is
        function Create return Base is (Size => 0, Ints => (others => 0));
        function Add_To (This : Base; I : Integer) return Base is
            -- This is where I have trouble: "aggregate cannot be of a class-wide type"
            Copy : Base := (Size => This.Size + 1, Ints => This.Ints & I);
        begin
            return Copy;
        end Add_To;
        function Image (This : Base) return String is ("BASE");
        function List (This : Base'Class) return Int_List is (This.Ints);
    end Bases;

package Deriveds is
        type Derived is new Bases.Base with  record
            Value : Integer;
        end record;
        function Create return Derived;
        function Add_To(This : Derived; I : Integer) return Derived;
        function Image (This : Derived) return String;
    end Deriveds;

package body Deriveds is
        function Create return Derived is (Bases.Create with Value => 0);
        function Image (This : Derived) return String is
            Result : Unbounded_String;
            Ints : Bases.Int_List := This.List;
        begin
            for I in Ints'Range loop
                Result := Result & Integer'Image (Ints (I));
            end loop;

return To_String (Result);
        end Image;
        function Add_To(This : Derived; I : Integer) return Derived is
        begin
            return (Bases.Base(This).Add_To(I) with Value => This.Value);
        end Add_To;
    end Deriveds;

use Deriveds;

d0 : Derived := Create;
    d1 : Derived := d0.Add_To(1).Add_To(3);
    d2 : Derived := d1.Add_To(2);

begin
  Put_Line(d2.Image);
end Hello;

</code>
  </pre>
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