oo programing help needed?

oo programing help needed?

[shoko]

i have the following:
------------------------------------------
package one is
  type one  is tagged private; 
  type one_ptr is access all one'class;
  
   procedure set_name(name:String;this:in out one);
  function  get_name(this:one) return string;
  
  private
     type one  is tagged 
     record
         name:String(1..256);
     end record;
  
   
end one ;
---------------------------------------------
with one;

package two is
   type two is new one.one with private ;
   private
      type two is new one.one with null record;
end two;
---------------------------------------------
with two;

package three is
   type three is new two.two with private ;
   function  get_name(this:three)  return string;
   private
      type three is new two.two with null record;
end two;      

-------------------------------------------
package body three is
   function get_name(this:three) return string
     s:string(1..10);
   begin
     return s+ this.name;  <-- no selector "name" for type three
  end get_name;

end three;


i get no selector "name" for type three

how to solve this problem??????

Re: oo programing help needed?

[Georg Bauhaus]

shoko <shoko2004@hotmail.com> wrote:
: i have the following:
: ------------------------------------------
: package one is
:  type one  is tagged private; 
:  type one_ptr is access all one'class;
:  
:   procedure set_name(name:String;this:in out one);
:  function  get_name(this:one) return string;
:  
:  private
:     type one  is tagged 
:     record
:         name:String(1..256);
:     end record;
:  
:   
: end one ;
...
: -------------------------------------------
: package body three is
:   function get_name(this:three) return string
:     s:string(1..10);
:   begin
:     return s+ this.name;  <-- no selector "name" for type three
:  end get_name;


In the definition of one in package one, you have chosen to
hide .name from view. But then you select a .name component
from within the body of package three, which as a package
is just any package, and thus cannot see the private
part of package one. (You could use get_name in three
because it is not in the private part of one. This might
be a good thing to do anyway as it respects the contract
for dealing with ones using one's public operations.)


-- Georg

Re: oo programing help needed?

[Stephen Leake]

Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de> writes:

> shoko <shoko2004@hotmail.com> wrote:
> : i have the following:
> : ------------------------------------------
> : package one is
> :  type one  is tagged private; 
> :  type one_ptr is access all one'class;
> :  
> :   procedure set_name(name:String;this:in out one);
> :  function  get_name(this:one) return string;
> :  
> :  private
> :     type one  is tagged 
> :     record
> :         name:String(1..256);
> :     end record;
> :  
> :   
> : end one ;
> ...
> : -------------------------------------------
> : package body three is
> :   function get_name(this:three) return string
> :     s:string(1..10);
> :   begin
> :     return s+ this.name;  <-- no selector "name" for type three
> :  end get_name;
> 
> 
> In the definition of one in package one, you have chosen to
> hide .name from view. But then you select a .name component
> from within the body of package three, which as a package
> is just any package, and thus cannot see the private
> part of package one. (You could use get_name in three
> because it is not in the private part of one. This might
> be a good thing to do anyway as it respects the contract
> for dealing with ones using one's public operations.)

Or, you can make packages Two and Three child packages of One; then
they have visibility to the private part of One.

Which approach is correct depends on what your full application is.

-- 
-- Stephe

Re: oo programing help needed?

[Steve]

"Stephen Leake" <stephen_leake@acm.org> wrote in message
news:mailman.29.1070719903.31149.comp.lang.ada@ada-france.org...
> Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de> writes:
>
> > shoko <shoko2004@hotmail.com> wrote:
> > : i have the following:
> > : ------------------------------------------
> > : package one is
> > :  type one  is tagged private;
> > :  type one_ptr is access all one'class;
> > :
> > :   procedure set_name(name:String;this:in out one);
> > :  function  get_name(this:one) return string;
> > :
> > :  private
> > :     type one  is tagged
> > :     record
> > :         name:String(1..256);
> > :     end record;
> > :
> > :
> > : end one ;
> > ...
> > : -------------------------------------------
> > : package body three is
> > :   function get_name(this:three) return string
> > :     s:string(1..10);
> > :   begin
> > :     return s+ this.name;  <-- no selector "name" for type three
> > :  end get_name;
> >
> >
> > In the definition of one in package one, you have chosen to
> > hide .name from view. But then you select a .name component
> > from within the body of package three, which as a package
> > is just any package, and thus cannot see the private
> > part of package one. (You could use get_name in three
> > because it is not in the private part of one. This might
> > be a good thing to do anyway as it respects the contract
> > for dealing with ones using one's public operations.)
>
> Or, you can make packages Two and Three child packages of One; then
> they have visibility to the private part of One.
>
> Which approach is correct depends on what your full application is.
>
> -- 
> -- Stephe
>
Another alternative (assuming get_name(this:one) does the obvious):

with one;
package body three is
   function get_name(this:three) return string is
     s:string(1..10);
   begin
     return s & one.get_name(one.one(this));
  end get_name;
end three;

BTW: It doesn't really take that much extra effort to actually run code you
post through the compiler.  If you had done so you would have had a few
other errors:

package three is
...
end two;      <-- Package name doesn't match

package body three is
   function get_name(this:three) return string  <-- Missing "is"
     s:string(1..10);

The "+" operator is not defined to concatenate two strings.  Use "&"
instead.

It's easy to save newsgroup posts and run gnatchop to get source files to
test.  It is annoying when the files generated don't compile due to errors
in the source.

Steve
(The Duck)

Re: oo programing help needed?

[Martin Krischik]

shoko wrote:

> i have the following:
> ------------------------------------------
> package one is
>   type one  is tagged private;
>   type one_ptr is access all one'class;
>   
>    procedure set_name(name:String;this:in out one);
>   function  get_name(this:one) return string;
>   
>   private
>      type one  is tagged
>      record
>          name:String(1..256);
>      end record;
>   
>    
> end one ;
> ---------------------------------------------
> with one;
> 
> package two is
>    type two is new one.one with private ;
>    private
>       type two is new one.one with null record;
> end two;
> ---------------------------------------------
> with two;
> 
> package three is
>    type three is new two.two with private ;
>    function  get_name(this:three)  return string;
>    private
>       type three is new two.two with null record;
> end two;
> 
> -------------------------------------------
> package body three is
>    function get_name(this:three) return string
>      s:string(1..10);
>    begin
>      return s+ this.name;  <-- no selector "name" for type three
>   end get_name;
> 
> end three;
> 
> 
> i get no selector "name" for type three
> 
> how to solve this problem??????

three is not a child packages of one. While it it true that "private" is
more like "protected" in C++ and Java it is also part of the package. So
only child packages can acces the private section - child classes can't do
that. Java has something similar but I can't remember the actual syntax
(something like private proctected or protected private or so).

With Regards

Martin

-- 
mailto://krischik@users.sourceforge.net
http://adacl.sourceforge.net

Re: oo programing help needed?

[Jeffrey Carter]

shoko wrote:
>      return s+ this.name;  <-- no selector "name" for type three

Where is "+" defined? If you haven't defined it, it doesn't exist, and 
this indicates that you need to learn Ada's basics better before you 
start messing around with its OO features.

-- 
Jeff Carter
"Mr. President, we must not allow a mine-shaft gap!"
Dr. Strangelove
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