[Info-vax] OO

[David Froble]

Stephen Hoffman wrote:
> On 2015-01-22 00:08:50 +0000, David Froble said:
> 
>> When does a module of code that performs a task stop being a module 
>> and becomes an object?
> 
> If you haven't spent some time with OO programming, this reply probably 
> won't make all that much sense.  But in VMS-ish terms, an "object" is 
> probably most similar to a shareable image, in that it's relatively 
> isolated from other hunks of code in the application, and with published 
> interfaces for the associated code and the data.  The shareable image 
> vectors, however, are resolved at run-time, which means that the 
> programmer can add or remove vectors easily, and can also override the 
> behavior of an existing object — these overrides are akin to easily 
> patching in a second shareable image that can then override some aspects 
> and can do things differently than the first shareable image, but while 
> still using most of the code from the first shareable image.  On the 
> fly.  You can also get callouts, where — when something happens to the 
> data, for instance — you can get notified of the change, and can then go 
> do something.  Without changing the code in the other object.    Like 
> shareable images, when you run an OO application, the run-time takes 
> care of merging all the pieces together, and applying the overrides and 
> performing the call-outs as needed.  Again, this is a whole lot easier 
> if you've used some OO tools.  OO can be brain-melting when first coming 
> over from traditional C, Fortran or BASIC code...  But OO is — much like 
> how compilers provided an abstraction over what assembler code provided 
> — a useful abstraction for some applications.
> 
> 

Brain melted ....