Object-oriented Software in Ada 95

Tasks 297
The implementation of the above program is split into two procedures. The procedure Do_Copy does the
actual work of copying between the two files.
with Ada.Text_Io, Pack_Threads, Pack_Types;
use Ada.Text_Io, Pack_Threads, Pack_Types;
procedure Do_Copy(From:in String; To:in String) is
type State is ( Open_File, Create_File );
Fd_In : P_File_Type := new Ada.Text_Io.File_Type;
Fd_Out : P_File_Type := new Ada.Text_Io.File_Type;
Mode : State := Open_File;
begin
Open( File=>Fd_In.all, Mode=>In_File, Name=>From);
Mode := Create_File;
Create(File=>Fd_Out.all, Mode=>Out_File, Name=>To);
declare
Buffers : P_PT_Buffer := new PT_Buffer ;
Reader : Task_Read( Buffers, Fd_In );
Writer : Task_Write( Buffers, Fd_Out );
begin
Reader.Finish; Close( Fd_In.all ); --Finish reader task
Writer.Finish; Close( Fd_Out.all ); --Finish writer task
end;
exception
when Name_Error =>
case Mode is
when Open_File =>
Put("Problem opening file " & From ); New_Line;
when Create_File =>
Put("Problem creating file " & To ); New_Line;
end case;
when Tasking_Error =>
Put("Task error in main program"); New_Line;
end Do_Copy;
Note: Explicit de-referencing of instances of a File_Type is achieved using .all.
The procedure copy extracts the arguments for the copy operation.
with Ada.Text_Io, Ada.Command_Line, Do_Copy;
use Ada.Text_Io, Ada.Command_Line;
procedure Copy is
begin
if Argument_Count = 2 then
Do_Copy ( Argument(1), Argument(2) );
else
Put("Usage: copy from to"); New_Line;
end if;
end Copy;
When a pointer to a protected type (for example, PT_Buffer) is elaborated, no object is created. The
creation of an instance of the protected type PT_Buffer is performed using new as follows:
Buffers : P_PT_Buffer := new PT_Buffer ;
Note:
As a protected object is limited, using an access value is one way of making the protected object visible
to several program units.
© M A Smith - May not be reproduced without permission