[Gm2] Extended opaque

[Chris Lilley]

Hello,

GM2 extends PIM and ISO Modula-2, allowing an opaque type to be any type rather 
than requiring it to be a pointer.

It seems to me that this is a good, type-safe extensio very much in the spirit 
of Modula-2. But, its a compiler-specific extension.

Was this added because it was an experiment, or to see if it worked, or because 
this feature should really have been in the standardized language?

Are others using this feature?

I recently made a module with a fully opaque type, then backed it out because I 
didn't want to depend on compiler specifics. But the resulting exposed, 
semi-opaque type seems less satisfactory to me.

I would be glad of thoughts or guidance from others on this feature.

-- 
 Chris Lilley   Technical Director, Interaction Domain                 
 W3C Graphics Activity Lead, Fonts Activity Lead
 Co-Chair, W3C Hypertext CG
 Member, CSS, WebFonts, SVG Working Groups