[M3devel] blue sky proposal :)

[Henning Thielemann]

On Sat, 22 Mar 2008, Tony Hosking wrote:

> Messing with VM protection mechanisms *will* impact performance, both to set 
> things up and to maintain.  For example, the GC needs to write to those pages 
> as it operates, so you are going to put extra work on the GC.  Yuck!
>
> Here is the germ of an alternative idea -- let add a READONLY declaration, 
> with enforcement by the compiler.   Should READONLY be a property of types? 
> i.e.,
>
> READONLY RECORD f: T;  g: T; END (* records of this type can never be 
> modified (i.e., f, g can only be initialized in a constructor) *)
>
> Or should READONLY be a property of designators?  i.e.,
>
> RECORD READONLY f: T; g: T END (* READONLY fields can never be modified 
> (i.e., f cannot be modified, but g can be modified) *)
>
> This needs fleshing out.  For example, if READONLY attaches to types, then 
> what are the assignment rules for non-readonly and readonly?  More 
> complicated still, what are the subtype rules?

Similar things are discussed in "Systems programming with Modula-3" by 
Greg Nelson et.al., aren't they?