Re: Private area and child packages

[Jeffrey Carter <spam@spam.com>]

danmcleran@hotmail.com wrote:

> Is there any way to hide implementation detail from child packages? An
> example, say I have a parent package like this:
> 
> package Some_Package is
> type Secret_Type is private;
> private
> type Secret_Type is record
> Secret_Value : Integer := 0;
> end record;
> end Some_Package;
> 
> I don't want any other component to be able to manipulate the
> Secret_Value record component, not even a child package of
> Some_Package.

If you don't need to make the type visible at all, you can simply 
declare it in the package body. Items in package bodies are hidden from 
all other scopes.

If you want the type to be visible, but its implementation to be hidden, 
you can use a pointer:

package P is
    type Something is [limited] private;

    -- operations on Something
private -- P
    type Implementation;
    type Something is access [all] Implementation;
end P;

The full view of Implementation must then be given in the body of P. If 
you do this, you're responsible for the memory management of Something. 
This is usually easier if you make Something limited, since the client 
cannot then make copies of the access values, eliminating opportunities 
for dangling references.

-- 
Jeff Carter
"Beyond 100,000 lines of code you
should probably be coding in Ada."
P. J. Plauger
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