Re: Initializers

["markww" <markww@gmail.com>]

Georg Bauhaus wrote:
> On Tue, 2006-12-19 at 18:02 -0800, markww wrote:
> > Hi everyone,
> >
> > I'm trying to compare C++ to Ada. I'm looking specifically at Ada's
> > lack of 'initializers'. I am guessing that this means there is no
> > 'constructor' to Ada packages maybe?
>
> Others have given examples of initialization of record components
> and of package initialization blocks. (Two different things.)
> Another 2c:
>
> There are also construction subprograms and nested Factory packages
> that are commonly used for initializing objects. Some of this is
> explained in the Ada wikibook, and in many Ada text books.
>
> In addition, consider:
>
> - types whose objects must not be initialised, not even default
>   initialized. A reason might be that their bits are mapped
>   to hardware. Initialization would mean sending signals to the
>   hardware. You don't want some signals sent only because the
>   language uses some default initialization. So in Ada, you can
>   turn initialization off, entirely.
>
> - limited types. For every object of a limited record you can
>   obtain its access within the record definition. This allows
>   one or more construction functions invoked automatically
>   when an object is created but not initialized "by hand":
>
>   package P is
>
>     type L is limited private;
>
>     package Factory is
>
>       function make(item: access L) return Natural;
>
>     end Factory;
>
>   private
>
>     type L is limited record
>       hook: Natural := Factory.make(L'access);
>       stuff: Integer;
>     end record;
>
>   end P;
>
>   Factory.make has access to all the components of its Item
>   parameter, including Stuff. It is invoked automatically
>   for an object of type L that isn't explicitly initialized.
>
> - discriminated types. These will force partial initialization
>   because the discriminant needs to have a value to make the
>   object be of some specific type, and have a known size etc.
>   There are some tricks here.
>
> - nested scope. This is useful if you compare initialization in
>   C++ and Ada because nesting is built into Ada and can be used
>   here. Support for nested scopes (dynamic + static) is limited
>   in C++ by comparison I think. There are cases where
>   you would pass parameters to a C++ constructor, where in Ada
>   you needn't pass them because they are in (local) scope.
>
>
>  -- Georg

Ok thanks for your replies. I also found this on 'elaboration':

    http://www.adapower.com/rm95/RM-7-6.html

where do you guys find examples of how to use these packages?

Thanks,
Mark