Re: Pb with use of redefined "=" operator

[Mats Weber <Mats.Weber@elca-matrix.ch>]

Matthew Heaney wrote:

> I make it a point that when I create a composite type --an abstract data
> type, or "open," as in your example-- that I guarantee equality will
> compose.
> 
> It is for this reason that I always implement (the full view of) ADTs as
> tagged, even if the partial view is not itself tagged.

But if you do that, then you don't need to explicitly import "=" as a
generic formal, because the reemergence problem does not exist with
(visibly or not) tagged types.

This also makes the following trick unnecessary:

> But the solution is trivial: just don't use equality for the composite
> type!  What I do is, always declare the equality for composite types as
> abstract:
> 
> [...]
>    type Pair is
>       record
>          X, Y : Item_Type;
>       end record;
> 
>   function "="
>     (L, R : Pair) return Boolean is abstract;