Re: Signature Package With Generic Proceedure

[Keean Schupke <keean.schupke@googlemail.com>]

On Monday, 23 July 2012 11:26:03 UTC+1, Simon Wright  wrote:
> Keean Schupke writes:
> 
> > If I have a package which defines a procedure like:
> >
> >
> > generic
> >     with procedure Process(Set : in out Set_Type);
> > procedure Update(Set : in out Set_Type);
> >
> >
> > How do a declare a Signature package that includes this?
> >
> >
> > generic
> >     with generic
> >         with procedure Process(Set : in out Set_Type);
> >     procedure Update(Set : in out Set_Type);
> > package Set_Signature is end;
> >
> >
> > Is not allowed. Is there some way to do this with nested packages?
> 
> I guess you meant to say
> 
>    generic
>        type Set_Type is limited private;
>        ...
>        with generic
>            with procedure Process(Set : in out Set_Type);
>        procedure Update(Set : in out Set_Type);
>        ...
>    package Set_Signature is end;
> 
> ? in which case I don't see why you couldn't say
> 
>    generic
>        type Set_Type is limited private;
>        ...
>        with procedure Update(Set : in out Set_Type);
>        ...
>    package Set_Signature is end;
> 
> Seems to me that all you need is for the actual Update to have that
> profile, who cares how it got that way?
> 
> I've probably misunderstood this. Could maybe child units help?
> 
>    generic
>       with procedure Process (Set : in out Set_Type);
>    procedure Set_Signature.Update (Set : in out Set_Type);

The Signature package defines the interface, so if the procedure in the signature is not generic, you could not instantiate it with the 'process' procedure you want to use.

Basically a signature package is like the first part of a package that has no body, and you bind it to another package later that actually provides the body.


Cheers,
Keean.