Re: 'Read for pointers

["Pat Rogers" <progers@NOclasswideSPAM.com>]

"Ted Dennison" <dennison@telepath.com> wrote in message
news:8lndgv$1om$1@nnrp1.deja.com...
> I've seen it suggested in several places to handle Stream writing of
> pointers by writing what the pointer points to instead. That's
simple
> enough.
>
> But say I want to make this automatic. Lets say I have a pointer
type
> declared thusly:
>
> package Example is
>    type Handle is private;
>
>    ...
> private
>
>    type Instance;
>
>    type Handle is access all Instance;
>
> end Example;
>
> The user doesn't even really know or care that Handle is really a
> pointer. But they may need to do stream I/O with it.
>
> The obvious solution is to create my own 'Write and 'Read routines
for
> Handle. But there's a problem. Following is the profile for 'Read:
>
>    procedure Read
>      (Stream : access Ada.Streams.Root_Stream_Type'Class;
>       Item   : out    Handle
>      );
>    for Handle'Read use Read;
>
> The problem is that Item is an *out* parameter. That means I won't
have
> acces to the pointer's old value inside Read. There's no way I can
put
> the newly read data from the stream into the Instance that Handle
> currently points to!

You can read mode out parameters in Ada 95 (unlike Ada 83).  (Am I
missing something?)

--
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