Ada：添加新元素时修改数组长度

Question

我尝试创建一个动态数组包。我有一个通用类型的通用包，然后我在 .ads 中声明了一个元素 Elem_Type 的数组（正索引）。我很好奇是否可以创建一个程序 Append(Vector, Item) 来修改 Vector 的长度，从而允许他再获取一个元素。就像你在 C 中有一个 buffer[100] 并给他分配 1 个元素使其成为 101 然后在位置 101 添加一些东西。

Answer 1

在 Ada 中，执行此操作的一般方法是创建一个新的更大的块，然后将内容复制到其中并释放旧块。我经常建议以一些大块大小的倍数分配新块，这样您就不必重新分配太多。所以如果你必须分配一个新数组，而不是只添加一个额外的元素，添加 500（或一些有意义的数字）。

请注意，即使在 C 中，realloc() 函数也经常执行此操作。 realloc() 函数实际上能够添加另一个元素，这在非平凡的项目中并不常见。它经常必须创建一个全新的数组并进行复制，就像我对 Ada 的建议一样。

Ada 中的一些其他选项包括制作您自己的存储池，使重新分配变得更容易和更快，但您必须想出如何执行此操作的算法或找到其他人。您也可以对 C 函数进行绑定，但不能将 malloc/realloc/free 与 Ada 的 new/unchecked_deallocation

混合使用

Answer 2

听起来您想使用通用包 Ada.Containers.Vectors，或者可能是包 Ada.Containers.Indefinite_Vectors。这些包已经定义了您似乎需要的所有功能。通用包的描述Ada.Containers.Vectors，如图Ada 2012 Reference Manual为

with Ada.Iterator_Interfaces;
generic
   type Index_Type is range <>;
   type Element_Type is private;
   with function "=" (Left, Right : Element_Type) return Boolean is <>;
package Ada.Containers.Vectors is
   pragma Preelaborate(Vectors);
   pragma Remote_Types(Vectors);

   subtype Extended_Index is
      Index_Type'Base range
         Index_Type'First-1 ..
         Index_Type'Min (Index_Type'Base'Last - 1, Index_Type'Last) + 1;
   No_Index : constant Extended_Index := Extended_Index'First;

   type Vector is tagged private
      with Constant_Indexing => Constant_Reference,
           Variable_Indexing => Reference,
           Default_Iterator  => Iterate,
           Iterator_Element  => Element_Type;
   pragma Preelaborable_Initialization(Vector);

   type Cursor is private;
   pragma Preelaborable_Initialization(Cursor);

   Empty_Vector : constant Vector;

   No_Element : constant Cursor;

   function Has_Element (Position : Cursor) return Boolean;

   package Vector_Iterator_Interfaces is new
       Ada.Iterator_Interfaces (Cursor, Has_Element);

   function "=" (Left, Right : Vector) return Boolean;

   function To_Vector (Length : Count_Type) return Vector;

   function To_Vector
     (New_Item : Element_Type;
      Length   : Count_Type) return Vector;

   function "&" (Left, Right : Vector) return Vector;

   function "&" (Left  : Vector;
                 Right : Element_Type) return Vector;

   function "&" (Left  : Element_Type;
                 Right : Vector) return Vector;

   function "&" (Left, Right  : Element_Type) return Vector;

   function Capacity (Container : Vector) return Count_Type;

   procedure Reserve_Capacity (Container : in out Vector;
                               Capacity  : in     Count_Type);

   function Length (Container : Vector) return Count_Type;

   procedure Set_Length (Container : in out Vector;
                         Length    : in     Count_Type);

   function Is_Empty (Container : Vector) return Boolean;

   procedure Clear (Container : in out Vector);

   function To_Cursor (Container : Vector;
                       Index     : Extended_Index) return Cursor;

   function To_Index (Position  : Cursor) return Extended_Index;

   function Element (Container : Vector;
                     Index     : Index_Type)
      return Element_Type;

   function Element (Position : Cursor) return Element_Type;

   procedure Replace_Element (Container : in out Vector;
                              Index     : in     Index_Type;
                              New_Item  : in     Element_Type);

   procedure Replace_Element (Container : in out Vector;
                              Position  : in     Cursor;
                              New_item  : in     Element_Type);

   procedure Query_Element
     (Container : in Vector;
      Index     : in Index_Type;
      Process   : not null access procedure (Element : in Element_Type));

   procedure Query_Element
     (Position : in Cursor;
      Process  : not null access procedure (Element : in Element_Type));

   procedure Update_Element
     (Container : in out Vector;
      Index     : in     Index_Type;
      Process   : not null access procedure
                      (Element : in out Element_Type));

   procedure Update_Element
     (Container : in out Vector;
      Position  : in     Cursor;
      Process   : not null access procedure
                      (Element : in out Element_Type));

   type Constant_Reference_Type
         (Element : not null access constant Element_Type) is private
      with Implicit_Dereference => Element;

   type Reference_Type (Element : not null access Element_Type) is private
      with Implicit_Dereference => Element;

   function Constant_Reference (Container : aliased in Vector;
                                Index     : in Index_Type)
      return Constant_Reference_Type;

   function Reference (Container : aliased in out Vector;
                       Index     : in Index_Type)
      return Reference_Type;

   function Constant_Reference (Container : aliased in Vector;
                                Position  : in Cursor)
      return Constant_Reference_Type;

   function Reference (Container : aliased in out Vector;
                       Position  : in Cursor)
      return Reference_Type;

   procedure Assign (Target : in out Vector; Source : in Vector);

   function Copy (Source : Vector; Capacity : Count_Type := 0)
      return Vector;

   procedure Move (Target : in out Vector;
                   Source : in out Vector);

   procedure Insert (Container : in out Vector;
                     Before    : in     Extended_Index;
                     New_Item  : in     Vector);

   procedure Insert (Container : in out Vector;
                     Before    : in     Cursor;
                     New_Item  : in     Vector);

   procedure Insert (Container : in out Vector;
                     Before    : in     Cursor;
                     New_Item  : in     Vector;
                     Position  :    out Cursor);

   procedure Insert (Container : in out Vector;
                     Before    : in     Extended_Index;
                     New_Item  : in     Element_Type;
                     Count     : in     Count_Type := 1);

   procedure Insert (Container : in out Vector;
                     Before    : in     Cursor;
                     New_Item  : in     Element_Type;
                     Count     : in     Count_Type := 1);

   procedure Insert (Container : in out Vector;
                     Before    : in     Cursor;
                     New_Item  : in     Element_Type;
                     Position  :    out Cursor;
                     Count     : in     Count_Type := 1);

   procedure Insert (Container : in out Vector;
                     Before    : in     Extended_Index;
                     Count     : in     Count_Type := 1);

   procedure Insert (Container : in out Vector;
                     Before    : in     Cursor;
                     Position  :    out Cursor;
                     Count     : in     Count_Type := 1);

   procedure Prepend (Container : in out Vector;
                      New_Item  : in     Vector);

   procedure Prepend (Container : in out Vector;
                      New_Item  : in     Element_Type;
                      Count     : in     Count_Type := 1);

   procedure Append (Container : in out Vector;
                     New_Item  : in     Vector);

   procedure Append (Container : in out Vector;
                     New_Item  : in     Element_Type;
                     Count     : in     Count_Type := 1);

   procedure Insert_Space (Container : in out Vector;
                           Before    : in     Extended_Index;
                           Count     : in     Count_Type := 1);

   procedure Insert_Space (Container : in out Vector;
                           Before    : in     Cursor;
                           Position  :    out Cursor;
                           Count     : in     Count_Type := 1);

   procedure Delete (Container : in out Vector;
                     Index     : in     Extended_Index;
                     Count     : in     Count_Type := 1);

   procedure Delete (Container : in out Vector;
                     Position  : in out Cursor;
                     Count     : in     Count_Type := 1);

   procedure Delete_First (Container : in out Vector;
                           Count     : in     Count_Type := 1);

   procedure Delete_Last (Container : in out Vector;
                          Count     : in     Count_Type := 1);

   procedure Reverse_Elements (Container : in out Vector);

   procedure Swap (Container : in out Vector;
                   I, J      : in     Index_Type);

   procedure Swap (Container : in out Vector;
                   I, J      : in     Cursor);

   function First_Index (Container : Vector) return Index_Type;

   function First (Container : Vector) return Cursor;

   function First_Element (Container : Vector)
      return Element_Type;

   function Last_Index (Container : Vector) return Extended_Index;

   function Last (Container : Vector) return Cursor;

   function Last_Element (Container : Vector)
      return Element_Type;

   function Next (Position : Cursor) return Cursor;

   procedure Next (Position : in out Cursor);

   function Previous (Position : Cursor) return Cursor;

   procedure Previous (Position : in out Cursor);

   function Find_Index (Container : Vector;
                        Item      : Element_Type;
                        Index     : Index_Type := Index_Type'First)
      return Extended_Index;

   function Find (Container : Vector;
                  Item      : Element_Type;
                  Position  : Cursor := No_Element)
      return Cursor;

   function Reverse_Find_Index (Container : Vector;
                                Item      : Element_Type;
                                Index     : Index_Type := Index_Type'Last)
      return Extended_Index;

   function Reverse_Find (Container : Vector;
                          Item      : Element_Type;
                          Position  : Cursor := No_Element)
      return Cursor;

   function Contains (Container : Vector;
                      Item      : Element_Type) return Boolean;


   procedure  Iterate
     (Container : in Vector;
      Process   : not null access procedure (Position : in Cursor));

   procedure Reverse_Iterate
     (Container : in Vector;
      Process   : not null access procedure (Position : in Cursor));

   function Iterate (Container : in Vector)
      return Vector_Iterator_Interfaces.Reversible_Iterator'Class;

   function Iterate (Container : in Vector; Start : in Cursor)
      return Vector_Iterator_Interfaces.Reversible_Iterator'Class;

   generic
      with function "<" (Left, Right : Element_Type)
         return Boolean is <>;
   package Generic_Sorting is

      function Is_Sorted (Container : Vector) return Boolean;

      procedure Sort (Container : in out Vector);

      procedure Merge (Target  : in out Vector;
                       Source  : in out Vector);

   end Generic_Sorting;

private

   ... -- not specified by the language

end Ada.Containers.Vectors;

Ada：添加新元素时修改数组长度

Ada: Array length modification when adding anew element

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allocation

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