Re: Limited object by reference or access argument?

[Jere <jhb.chat@gmail.com>]

On Sunday, August 6, 2017 at 5:16:37 PM UTC-4, Victor Porton wrote:
> Suppose we have
> 
> type World_Type is tagged limited private;
> 
> type BNode_ID_Handler is abstract tagged limited private;
> 
> We need to set a bnode handler for a world object. Should the procedure 
> signature be
> 
> procedure Set_Handler (World: World_Type;
>                        Handler: access BNode_ID_Handler'Class);
> 
> or 
> 
> procedure Set_Handler (World: World_Type;
>                        Handler: BNode_ID_Handler'Class);
> 
> The later can work with limited BNode_ID_Handler type, because tagged and 
> limited types are always passed by reference.
> 
> I prefer the second one, because with the first procedure signature it is 
> possible to pass an access to an already finalized object what is an error, 
> but want to ask you opinion which of the two procedure signatures is better.
> 
> -- 
> Victor Porton - http://portonvictor.org

You can also just make it tagged (Ada95 to present) or denote the 
procedure parameter as aliased (Ada2012):

procedure Set_Handler (World: World_Type;
                        Handler: aliased in out BNode_ID_Handler'Class);

I am not sure of the limitations to that as it is a new feature I 
am less experienced with.