[Info-vax] Access to _all_ VMS system services and library functions from DCL ?

[David Froble]

Simon Clubley wrote:
> On 2017-07-10, David Froble <davef at tsoft-inc.com> wrote:
>> Well, not just for DCL.  Have defined blocks of data for each system service. 
>> Either I allocate the memory, (probably best) or have the system service 
>> allocate the memory.  Then jam it full of all data provided by that system 
>> service.  Sure would do away with item lists, at least to some extent.
>>
> 
> A single block of data which is directly accessed is too limiting and
> will cause massive maintainence problems as structures are changed and
> field sizes changed in the future.

Why?

> This will lead to a different version of the data block for every
> change in the future and all these versions would have to be kept
> around in the future as well as the code to populate them.

Why?

> There is a strong argument for an easier than currently exists method
> to get at this data, but there still needs to be some level of abstraction
> in order to be able to handle these issues.

I thought what I suggested was rather abstract.

> Oh, and for something like this, if it was done anyway, there's no way
> you should pass in the memory to be used. For a structure this complex,
> VMS would need to control the memory it was writing to for safety reasons
> and that means it allocates the memory and returns a pointer to it.

As I mentioned, it could be done either way.  I believe that the option of 
including the data block definition into a program and then passing the data 
block to be populated is a valid method.  If I passed it by Descriptor, the SS 
could validate the size and such.

>> If I can "include" the data structure in my programs, and then reference the 
>> data by name, sure would make things simpler.
> 
> And what about when the data block is changed because a field is
> expanded (for example) ?

This is something VSI should be able to do.  Modify the data block as required. 
  That would include different field sizes.

I haven't given this a tremendous amount of thought.  Just some thoughts I've 
had.  Any implementation would of course require much more study and design 
work.  Got to prevent nefarious activity.