🚀 go-pugleaf

In article <24878@sophia.inria.fr>, huitema@mitsou.inria.fr (Christian Huitema) writes:

|> 
|> 4) Regarding "extensible" data types, as mentioned by Bancroft Scott. We seem
|> to have a problem here. Take the exemple of a type:
|>    X ::= SEQUENCE {
|>      a[0] Foo,
|>      b[1] Bar }
 
   To allow the above expression to be extensible.  Currently in the standards,
   the typical way is to add a clause as below:
 
      "The abstract syntax name may be used when the presentation data values 
       are modified to include
  
       ....
       - new tagged elements within a SEQUENCE;
       ..."
 
   I assume the existing compiler which supports the extensibility rules
   will need to use a compiler-specific directive to mark that X is extensible.
   There is a CD corrigendum for X.208 to use format syntax to express 
   extensible. For example, 
    

      X ::= SEQUENCE {
 	a[0] Foo,
	b[1] Bar, ... }	
 

|> Which get extented in a revised version of a protocol into:
|>    X ::=SEQUENCE {
|>      a[0] Foo,
|>      b[1] Bar,
|>      c[2] NewData OPTIONAL } 
|> I would suppose that the initial version is translated in C as:
|>   typedef struct {
|> 	  Foo a,
|> 	  Bar b }
 
   The initial version may be translated in C as:
 
     typedef struct {
          Foo  a,
          Bar  b,
          Any  extension }
   since it is known to be extensible in contrast to the expression for a
   non-extensible SEQUENCE.

|> Now, just explain me how I am supposed to pass information on the extra
|> component "NewData", should it be present?
|> 

   See above.


Wei-Lee