Generic package parameters not externally visible : what's the rational ?

["Hibou57 (Yannick Duchêne)" <yannick_duchene@yahoo.fr>]

Hello ghosts out there,

24h without even a single post on comp.lang.ada... I hope every body
is Ok.

Still the time for my two cents of the day : parameters of generic
packages are not externally visible. I use to read in a few places on
the web, this is so to preserve type privacy, but without any examples
which could illustrate this view.

What's the rational behind this ?

I like to do something like this to work around this :

generic

   Parameter_Type is (<>);

   -- Other generic parameters ...

package Generic_Package is

   -- Give external access to generic parameters which are not visible
otherwise.

   subtype Formal_Parameter_Type is Parameter_Type

   -- The same for other generic parameters ...

   -- Remaining of the package ...

end Generic_Package;

I feel it is oftenly useful to have external access to generic
parameters : it is more clear and more consistent than making
reference to stuffs from different source (finally, the package
instance is a place where all these references are available, so why
not use these). I feel this is especially useful when other generic
packages are instantiated using the same parameters used to
instantiate another generic packages.

That's why I was wondering about the rational which is underlying to
this restriction (the one which disallows a generic parameter to be
externally visible).

Have a nice time (if every one is Ok).