Re: Quick question regarding limited type return syntax

[Adam Beneschan <adambeneschan@gmail.com>]

On Wednesday, July 30, 2014 6:00:43 PM UTC-7, NiGHTS wrote:
> On Wednesday, July 30, 2014 8:48:34 PM UTC-4, Shark8 wrote:
> 
> > On 30-Jul-14 17:51, NiGHTS wrote:
> 
> > >   return  Object (Connection_String'Access) do null; end return;

> package body Test is
>    function Create(...) return Object is
>       ...
>    begin
>       return Object'(Connection_String'Access);
>    end;
>    ...
> end Test;

What you need to do is return an aggregate.  And to return an aggregate, you need to specify both fields--the Parameters discriminant and the Database.  This syntax:

    Object'(Connection_String'Access)

is just wrong.  It tells the compiler that the value is Connection_String'Access, and asks the compiler to treat it as an Object.  It can't do that, because Object isn't an access type.  (This sort of syntax can be useful in overloading cases, when the compiler can't determine the correct access type without help.)

If you said

    Object'(Parameters => Connection_String'Access)

you'd get an error that Database is missing.  So you need

    Object'(Parameters => Connection_String'Access, Database => <>)

or just

    (Parameters => Connection_String'Access, Database => <>)

or    

    (Parameters => Connection_String'Access, others => <>)

(It's OK for a function that returns a limited type to return an aggregate like this.)

The effect is that subcomponents of Database that have default initial values will be initialized, and subcomponents that don't have default initial values will be initialized to garbage (except where the language says otherwise).  That's really the same as your original example was trying to do.  I guess that explicitly putting "others => <>" in an aggregate is enough to convince GNAT not to think you were accidentally leaving something initialized to garbage.  

                              -- Adam