Re: [student help] Won't allow package body.

Re: [student help] Won't allow package body.

[David C. Hoos, Sr.]

Oliver White wrote in message <35514AAC.D46B535C@iinet.net.au>...
>I'm compiling a package, the ads file begins as so -
>
>> generic
>> type ObjectType is private;
>> package LinkedListPackage is
>>
>but when I compile, I get this message -
>
>"generic package LinkedListPackage does not allow a body"
>
This is either one of two things:
    1.  The package does not allow a body because none is required -- e.g.,
the package spec defines no subprogram, so no body is required.  If no body
is required, none is allowed.

    2.  There is an error of some sort in the code which prevents error-free
compilation of the package spec.  Then, in may cases you will get this
error.

In general, you need to provide a complete compilation unit in your request
for help, because there is not enough  information in an incomplete code
snippet such as you have supplied to answer your question.  Also, as a
general rule, you should tell us what is the compiler and version you are
using, and on what platform.

With complete information, I' sure one of us will be glad to help.

David C. Hoos, Sr.

Re: [student help] Won't allow package body.

[MSG]

Besides the fact that Davic C Hoos, Sr. is correct and that you need to
provide a more complete example...

Assuming that your spec is compilable but doesn't require a body (a generic
with no body?...I'll have to think about that later)...you can force need
for a body by adding a dummy procedure with no code OR you can specify
"pragma Elaborate_Body;" in the spec of the generic pacakge.

Michael Garnett

Oliver White <ojw@iinet.net.au> wrote in message
35514AAC.D46B535C@iinet.net.au...
I'm compiling a package, the ads file begins as so -


generic

   type ObjectType is private;

package LinkedListPackage is
but when I compile, I get this message -
"generic package LinkedListPackage does not allow a body"

I'm sure there's an obvious error, could you help me?

Oliver White.

Re: [student help] Won't allow package body.

[Brian Rogoff]

On Wed, 13 May 1998, MSG wrote:

> Besides the fact that Davic C Hoos, Sr. is correct and that you need to
> provide a more complete example...
> 
> Assuming that your spec is compilable but doesn't require a body (a generic
> with no body?...I'll have to think about that later)...you can force need

Bodiless generics are part of a very powerful Ada programming idiom. Using
them we can decouple interfaces (signatures) from implementations. For
example, here is a pseudo-Ada outline of a sequence type, showing roughly
how it might be used.

generic
   type Item_Type is private;
   type Position_Type is private;
   type Sequence_Type is private;
   with procedure Initialize (Seq : out Sequence_Type);
   with function  Is_Empty (Seq : Sequence_Type) 
			    return Boolean is private;
   with function  Is_Done (Seq : Sequence_Type; Pos : Position_Type) 
			   return Boolean is private;
package Sequence_Sig is 
-- Here is your bodiless generic!
end;


generic
   type Item_Type is private;
package Lists is
   type Position_Type is private;
   type List_Type is private;

   with procedure Initialize (Seq : out Sequence_Type);
   with function  Is_Empty (Seq : Sequence_Type) 
			    return Boolean;
   with function  Is_Done (Seq : Sequence_Type; Pos : Position_Type) 
			   return Boolean;
   
   with function  Get_Value_At (Seq : Sequence_Type; Pos : Position_Type) 
			   return Item_Type;
   
   with function  Succ (Pos : Position_Type) return Position_Type;
   
private
   -- Singly linked list implementation
end;

package Integer_Lists is new Lists(Item_Type => Integer);

package Integer_Seqs is 
  new Sequences(Item_Type     => Integer_Lists.Item_Type,
		Position_Type => Integer_Lists.Position_Type,
		Sequence_Type => Integer_Lists.List_Type,
		Initialize    => Integer_Lists.Initialize
                ... etc...
                );

generic 
   with Concrete_Seqs is new Sequences(<>);
package Concrete_Algorithms is 
...
end Concrete_Algorithms;

A client package like Concrete_Algorithms will only depend on the
Signature and so you can substitute arrays or lists or vectors or 
whatever as your sequence. 

-- Brian

> for a body by adding a dummy procedure with no code OR you can specify
> "pragma Elaborate_Body;" in the spec of the generic pacakge.
> 
> Michael Garnett
> 
> Oliver White <ojw@iinet.net.au> wrote in message
> 35514AAC.D46B535C@iinet.net.au...
> I'm compiling a package, the ads file begins as so -
> 
> 
> generic
> 
>    type ObjectType is private;
> 
> package LinkedListPackage is
> but when I compile, I get this message -
> "generic package LinkedListPackage does not allow a body"
> 
> I'm sure there's an obvious error, could you help me?
> 
> Oliver White.
> 
> 
> 
> 
>