Iterator Interface, Ada

Iterator Interface

--GNAT 4.9.3

with Ada.Text_IO;
with Ada.Iterator_Interfaces;
with system;
with System.Address_To_Access_Conversions;

procedure Hello is

type Integer_Array is array (Positive range <>) of aliased Integer;

type list(cnt : positive) is record
        data : Integer_Array(1..cnt);
    end record;
    
    package Address_Conversions is new System.Address_To_Access_Conversions (list);
    
    type cursor is record
        container : system.address;
        index : integer;
    end record;
    
    function has_element(position : cursor) return boolean is
        l : list renames Address_Conversions.To_Pointer(position.container).all;
    begin
        return position.index <= l.data'length;
    end has_element;
    
    package Iterators is new Ada.Iterator_Interfaces (Cursor, Has_Element);
    
    type iterator is new iterators.forward_iterator with record
        container : system.address;
    end record;
    
     function First (iter : Iterator) return Cursor;
     function Next (iter : Iterator; Pos : Cursor) return Cursor;
     
    function Iterate (container : list) return Iterators.Forward_Iterator'Class is
    begin
        return iter : iterator do
            iter.container := container'address;
        end return;
    end iterate;
    
    function First (iter : Iterator) return Cursor is
   begin
      return C : Cursor do
         C.container := iter.container;
         C.index := 1;
      end return;
   end First;

function Next (iter : Iterator; Pos : Cursor) return Cursor is
   begin
      return C : Cursor do
         C.container := Pos.container;
         C.index := Pos.index + 1;
      end return;
   end Next;

type reference_type(element :  not null access integer) is limited null record
    with Implicit_Dereference => element;

function get (C : Cursor) return reference_type is
      S : list renames Address_Conversions.To_Pointer (C.container).all;
   begin
      return reference_type'(element=>s.data(c.index)'access);
   end get;
  
    l : list :=(data=>(1,2,3,4,5,6,7,8,9,10), cnt=>10);           
begin

for c in iterate(l) loop
    ada.text_io.put_line(integer'image(get(c)));
   end loop;

end Hello;


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