packet type ?

packet type ?

[Alfred Hilscher]

Hi all,

I am not so familiar with the OO-extensions of Ada95 so maybe my
question is obsolete. What I'm looking for is something like a "packege
type" (similar to "task type"). What I want do is something like this:

package type stack is
  push (item : in ...);
  pop  (item : out ...)
end stack

procedure application is
  User_stack : stack;
  Supervisor_stack : stack;
  Interrupt_stack : stack;
begin
 ...
end application;


Any suggestions how to do this ?

Re: packet type ?

[Ted Dennison]

In article <387F3DD1.485F7C70@icn.siemens.de>,
  Alfred Hilscher <Alfred.Hilscher@icn.siemens.de> wrote:
> Hi all,
>
> I am not so familiar with the OO-extensions of Ada95 so maybe my
> question is obsolete. What I'm looking for is something like a
"packege
> type" (similar to "task type"). What I want do is something like this:

> Any suggestions how to do this ?

That's what generics with package formal parameters are for.

--
T.E.D.

http://www.telepath.com/~dennison/Ted/TED.html


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Re: packet type ?

[Alfred Hilscher]

Ted Dennison wrote:
> 
> > question is obsolete. What I'm looking for is something like a
> "packege
> > type" (similar to "task type"). What I want do is something like this:
> 
> > Any suggestions how to do this ?
> 
> That's what generics with package formal parameters are for.


I think thats not quite the same. Taking the example below, how would
you do this with generics ?


package type stack is
  push (item : in ...);
  pop  (item : out ...)
end stack

procedure application is
  User_stack : stack;
  Supervisor_stack : stack;
  Interrupt_stack : stack;

  Any_Stack : access Stack;
begin
 ...
  Any_Stack := new Stack; -- how do this  ???
 ...
end application;

Re: packet type ?

[Brian Rogoff]

On Tue, 18 Jan 2000, Alfred Hilscher wrote:
> Ted Dennison wrote:
> > 
> > > question is obsolete. What I'm looking for is something like a
> > "packege
> > > type" (similar to "task type"). What I want do is something like this:
> > 
> > > Any suggestions how to do this ?
> > 
> > That's what generics with package formal parameters are for.
> 
> 
> I think thats not quite the same. Taking the example below, how would
> you do this with generics ?
> 
> 
> package type stack is
>   push (item : in ...);
>   pop  (item : out ...)
> end stack
> 
> procedure application is
>   User_stack : stack;
>   Supervisor_stack : stack;
>   Interrupt_stack : stack;
> 
>   Any_Stack : access Stack;
> begin
>  ...
>   Any_Stack := new Stack; -- how do this  ???
>  ...
> end application;

Packages are not first class entities in Ada. They cannot be assigned to
variables or passed as function arguments. The closest you get is as
T.E.D. suggested, by using generic formal package parameters which give
you a small language for combining the packages.

What is there that you wished to do with first class packages that you
couldn't do equally nicely with plain old ADTs, maybe even using tagged
types to be fancy :-). The stack example is easily programmed that way.

-- Brian

Re: packet type ?

[Ted Dennison]

In article <38845EBD.6F90845D@icn.siemens.de>,
  Alfred Hilscher <Alfred.Hilscher@icn.siemens.de> wrote:
>
> Ted Dennison wrote:
> I think thats not quite the same. Taking the example below, how would
> you do this with generics ?
>
> package type stack is
>   push (item : in ...);
>   pop  (item : out ...)
> end stack
>
> procedure application is
>   User_stack : stack;
>   Supervisor_stack : stack;
>   Interrupt_stack : stack;
>
>   Any_Stack : access Stack;
> begin
>  ...
>   Any_Stack := new Stack; -- how do this  ???
>  ...
> end application;

The flip answer is I'd download the Booch components. :-)

Code wise, I'd do something like this:

generic
   type Element is private;
package Stack is
   type Instance is private;

   Push (Item : in Element
         Onto : in out Instance);
   Pop  (Item   :    out Element;
         Off_Of : in out Instance);
private
...
end Stack;

It looks like your confusion is based on experience w/ other OO-based
languages. In Ada types and packages are completely separate kinds of
entities. Packages exist to provide for organizing other things into a
single namespace. Types define the data structure of objects.
Subprograms are defined within the context of packages, not types or
objects. For instance, to call what I created above, first I'd
instantiate it with my element type thusly:
   with Stack;
   ...
   procedure Whatever is
      package Integer_Stack is new Stack (Integer);

Then I call push this way:
      Pushee : Integer := 20;
      Old_Integers : Integer_Stack.Instance;
      ...
   begin
      Integer_Stack.Push (Item => Pushee,
                          Onto => Old_Integers);

--
T.E.D.

http://www.telepath.com/~dennison/Ted/TED.html


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Before you buy.

Re: packet type ?

[Brian Rogoff]

On 19 Jan 2000, Anders Gidenstam wrote:
> Well, you make a generic package containing the stack ADT.
> It'll be something like this:
> 
> generic
> 	type Element_Type is private;
> package Stack_ADT is
> 
> 	type Stack(Size : Natural) is private;
> 
> 	procedure Push (S : in out Stack; I : in  Element_Type);
> 	procedure Pop  (S : in out Stack; I : out Element_Type);
> 	
> 	...
> 
> private
> 	type Element_Array is array (Positive range <>) of Element_Type;
> 
> 	type Stack(Size : Natural) is
> 		record
> 			S   : Element_Array (1..Size);
> 			Top : Natural := 0;
> 		end record;
> end Stack_ADT;
> 
> And you use it like this:
> 
> with Stack_ADT;
> procedure Something is
> 
> 	package Integer_Stack is new Stack_ADT (Integer);
> 	use 	Integer_Stack;
> 	package Float_Stack is new Stack_ADT (Float);
> 	use 	Float_Stack;
> 
> 
> 	My_Stack : Integer_Stack.Stack (Size => 100);
> 	Some_Stack : Float_Stack.Stack (Size => 50);
> begin
> 	Push (My_Stack, 3);
> 	Push (Some_Stack, 7.0);
> 	...
> 
> I hope this was helpful in understanding this part of Ada.
> (Note that this isn't OO in the C++ sense, you can't let any type inherit 
>  the stack's properties but I don't think that type of inheritance is needed 
>  for an ADT like this. And of course one could make the stack a tagged type
>  which would allow inheritance.)

Ada 95 also allows you to create a stack signature 

generic 
    type Item_Type is private;
    type Stack_Type is private;
    with procedure Push(Stack : in out Stack_Type; Item : in Item_Type);
    with procedure Pop(Stack : in out Stack_Type; Item : out Item_Type);
    ...
package Stack_Sig is begin end;

and write code which only depends on an instantiation having that profile,
so that your stack code and many others can supply the stack ADT for the 
code. This is a very nice feature of Ada 95 which is not described in many 
Ada books; Barnes and Ben-Ari are exceptional here.

-- Brian

Re: packet type ?

[Anders Gidenstam]

In article <38845EBD.6F90845D@icn.siemens.de>,
	Alfred Hilscher <Alfred.Hilscher@icn.siemens.de> writes:
> 
> Ted Dennison wrote:
>> 
>> > question is obsolete. What I'm looking for is something like a
>> "packege
>> > type" (similar to "task type"). What I want do is something like this:
>> 
>> > Any suggestions how to do this ?
>> 
>> That's what generics with package formal parameters are for.
> 
> 
> I think thats not quite the same. Taking the example below, how would
> you do this with generics ?
> 
> 
> package type stack is
>   push (item : in ...);
>   pop  (item : out ...)
> end stack
> 
> procedure application is
>   User_stack : stack;
>   Supervisor_stack : stack;
>   Interrupt_stack : stack;
> 
>   Any_Stack : access Stack;
> begin
>  ...
>   Any_Stack := new Stack; -- how do this  ???
>  ...
> end application;

Well, you make a generic package containing the stack ADT.
It'll be something like this:

generic
	type Element_Type is private;
package Stack_ADT is

	type Stack(Size : Natural) is private;

	procedure Push (S : in out Stack; I : in  Element_Type);
	procedure Pop  (S : in out Stack; I : out Element_Type);
	
	...

private
	type Element_Array is array (Positive range <>) of Element_Type;

	type Stack(Size : Natural) is
		record
			S   : Element_Array (1..Size);
			Top : Natural := 0;
		end record;
end Stack_ADT;

And you use it like this:

with Stack_ADT;
procedure Something is

	package Integer_Stack is new Stack_ADT (Integer);
	use 	Integer_Stack;
	package Float_Stack is new Stack_ADT (Float);
	use 	Float_Stack;


	My_Stack : Integer_Stack.Stack (Size => 100);
	Some_Stack : Float_Stack.Stack (Size => 50);
begin
	Push (My_Stack, 3);
	Push (Some_Stack, 7.0);
	...

I hope this was helpful in understanding this part of Ada.
(Note that this isn't OO in the C++ sense, you can't let any type inherit 
 the stack's properties but I don't think that type of inheritance is needed 
 for an ADT like this. And of course one could make the stack a tagged type
 which would allow inheritance.)

/Anders
-- 
"A well-written program is its own heaven; 
 a poorly-written program is its own hell."
  - The Tao of Programming 

Re: packet type ?

[Brian Rogoff]

Quite sure, but you have to fix my syntax error. :-)

-- Brian

On Thu, 20 Jan 2000, Andy S wrote:

> Brian Rogoff wrote:
> > Ada 95 also allows you to create a stack signature
> > 
> > generic
> >     type Item_Type is private;
> >     type Stack_Type is private;
> >     with procedure Push(Stack : in out Stack_Type; Item : in Item_Type);
> >     with procedure Pop(Stack : in out Stack_Type; Item : out Item_Type);
> >     ...
> > package Stack_Sig is begin end;
> > 
> > and write code which only depends on an instantiation having that profile,
> > so that your stack code and many others can supply the stack ADT for the
> > code. This is a very nice feature of Ada 95 which is not described in many
> > Ada books; Barnes and Ben-Ari are exceptional here.
> > 
> Are you sure? My GNAT compiler barffed at this one !
> 
> ___________________________________________
> 
>    Andy Starritt
> ___________________________________________
> 

Re: packet type ?

[Andy S]

Brian Rogoff wrote:
> Ada 95 also allows you to create a stack signature
> 
> generic
>     type Item_Type is private;
>     type Stack_Type is private;
>     with procedure Push(Stack : in out Stack_Type; Item : in Item_Type);
>     with procedure Pop(Stack : in out Stack_Type; Item : out Item_Type);
>     ...
> package Stack_Sig is begin end;
> 
> and write code which only depends on an instantiation having that profile,
> so that your stack code and many others can supply the stack ADT for the
> code. This is a very nice feature of Ada 95 which is not described in many
> Ada books; Barnes and Ben-Ari are exceptional here.
> 
Are you sure? My GNAT compiler barffed at this one !

___________________________________________

   Andy Starritt
___________________________________________

Re: packet type ?

[Tucker Taft]

Andy S wrote:
> 
> Brian Rogoff wrote:
> > Ada 95 also allows you to create a stack signature
> >
> > generic
> >     type Item_Type is private;
> >     type Stack_Type is private;
> >     with procedure Push(Stack : in out Stack_Type; Item : in Item_Type);
> >     with procedure Pop(Stack : in out Stack_Type; Item : out Item_Type);
> >     ...
> > package Stack_Sig is begin end;
> >
> > and write code which only depends on an instantiation having that profile,
> > so that your stack code and many others can supply the stack ADT for the
> > code. This is a very nice feature of Ada 95 which is not described in many
> > Ada books; Barnes and Ben-Ari are exceptional here.
> >
> Are you sure? My GNAT compiler barffed at this one !

Try removing the "..." and the "begin" from the above.

> __________________________________________
> 
>    Andy Starritt
> ___________________________________________

-- 
-Tucker Taft   stt@averstar.com   http://www.averstar.com/~stt/
Technical Director, Distributed IT Solutions  (www.averstar.com/tools)
AverStar (formerly Intermetrics, Inc.)   Burlington, MA  USA