Re: Assigning a "subclass" instance to a "superclass" variable

[deuteros <deuteros@xrs.net>]

On Fri 06 Apr 2012 05:50:18p, Simon Wright <simon@pushface.org> wrote in
news:m2ty0wh6n9.fsf@pushface.org: 

>    with Statements;
>    package Expressions is
>       type Expression is new Statements.Statement with record
>          ...
>       end record;
>       function Execute (Skip : Boolean; S : Expression) return Integer;
>    end Expressions;
> 
> or
> 
>    package Statements.Expressions is
>       type Expression is new Statement with record
>          ...
>       end record;
>       function Execute (Skip : Boolean; S : Expression) return Integer;
>    end Statements.Expressions;
> 
> The second form is good if the full declaration of Statement is in the
> private part of Statements, since child packages can see the private
> parts of their parents.

Okay, so would I need to put tokens and executedtokens in Expression's
record as well or would it somehow inherit them from Statements? 

I want something like a constructor in my child classes:

    	function Create_Expression (tokens, executedtokens : Vector) return Expression is
    	    	E : Expression
    	begin
    	    	E.tokens := tokens;
    	    	E.executedtokens := executedtokens;
    	    	return E;
    	end Create_Expression;

Now if the Expression package must have its own tokens and executedtokens
I assume this would be the way to do it but if not then how would this
work?