Re: Q: Hiding the structure of a tagged type using containers

["Matthew Heaney" <mheaney@on2.com>]

Stephen Leake wrote:
> brian.b.mcguinness@lmco.com writes:
>
>
> The general solution to this error is to make one of the arguments
> class-wide; in this case:
>
> procedure Shape
>    (A : in APL_Array_Dimensioned; Dimensions : out APL_Shape'class);

This won't work, since the APL_Shape isn't tagged at the point where
Shape is declared.


> Another solution is to use only one tagged type. Apparently
> APL_Dimension_List.Vector is visibly tagged; perhaps it does not need
> to be?

We debated this during the design of the container library, and
concluded that we might as well make the type tagged, since the most
likely implementation would be that container types privately derive
from Controlled.  Making the container types publicly tagged then gives
you other benefits such as as implicit aliasing of subprogram
parameters and distinguished-receiver syntax.

The solution in this case is to implement the full view of type
APL_Shape as a non-tagged record, with a vector component.

-Matt