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Re: save ... restore? setglobal?

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On Friday, March 25, 2016 at 11:05:17 AM UTC-5, jdaw1 wrote:
> I maintain a large PostScript program (≈ 12.7k lines). http://www.jdawiseman.com/placemat.html
> It does not use save … restore. Indeed, I have never used save … restore in any PostScript program. 
> 
> Do you use save … restore? What for? For what should I be using it? 
> 
> And yes, I have read §3.7.3, pp61-62, of PLRM3. 
> 
> Relatedly, I never use setglobal. Do you use setglobal? What for? For what should I be using it?

`save` and `restore` can be used to bracket sections of
the program which allocates memory that is not needed
after the `restore`. For instance, if you have a "normal"
document (not necessarily DSC-compliant, but roughly laid
out the same) with a prologue section and several distinct
pages, then you can put `save` ... `restore` around each
page description. The memory allocated while executing the
page will be rewound to the same state (mostly).

Since Level 2, postscript has garbage collection, so this
isn't strictly necessary for memory management. But 
judicious use of `save` and `restore` could reduce the
burden on the collector somewhat, with an effect on the
speed of execution.


Also introduced in Level 2 is global memory. This is a 
separate memory space which is not (normally) affected
by `save` and `restore`. You'll only need to use global
memory if you're doing something like defining a resource
or some other special structure which must persist past
the lifetime of any local objects which `restore` might
discard. 

Because local memory is more perishable, there is the
rule that arrays and dicts in global memory cannot contain
references to objects in local memory (because they might
arbitrarily disappear at any time).

tldr; Use `save`...`restore` to rewind the values of all
arrays and dicts to their contents at the time of the `save`.
Use `setglobal` (correctly) if you're trying to use
`defineresource`.

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save ... restore? setglobal? jdaw1 <jdawiseman@gmail.com> - 2016-03-25 09:05 -0700
  Re: save ... restore? setglobal? luser- -droog <mijoryx@yahoo.com> - 2016-03-25 09:32 -0700
    Re: save ... restore? setglobal? jdaw1 <jdawiseman@gmail.com> - 2016-03-25 10:41 -0700
      Re: save ... restore? setglobal? luser- -droog <mijoryx@yahoo.com> - 2016-03-25 11:16 -0700
        Re: save ... restore? setglobal? jdaw1 <jdawiseman@gmail.com> - 2016-03-25 11:41 -0700
          Re: save ... restore? setglobal? Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-02 02:38 -0700
            Re: save ... restore? setglobal? luser- -droog <mijoryx@yahoo.com> - 2016-06-02 16:08 -0700
        Re: save ... restore? setglobal? Martin Leese <please@see.Web.for.e-mail.INVALID> - 2016-03-26 12:07 -0600
  Re: save ... restore? setglobal? Markus Triska <triska@metalevel.at> - 2016-03-26 09:12 +0100
    Re: save ... restore? setglobal? jdaw1 <jdawiseman@gmail.com> - 2016-03-26 06:37 -0700
      Re: save ... restore? setglobal? Markus Triska <triska@metalevel.at> - 2016-03-27 14:51 +0200
  Re: save ... restore? setglobal? sjprouty3765@gmail.com - 2016-03-28 12:40 -0700

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