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Variable scope

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  • January 4, 2016 at 6:55 pm #54932
    David Coffey
    Participant

      In working with TCL procs I find that if I declare a variable as global in one proc a similarly named variable in another proc(same thread) is updated.  In other words using a global variable with the same name in multiple procs in a thread, which ever proc updated the variable last, this is reflected in all other procs.  

      How can I set a variable to be global only in the scope of the proc without resorting to unique names in each and every proc in my library?  

      Hope this makes sense!

      David Coffety

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      • January 4, 2016 at 11:23 pm #83498
        Charlie Bursell
        Participant

          This is true if in the same Tcl interpreter

          I suggest you use namespaces

        • January 4, 2016 at 11:45 pm #83499
          David Coffey
          Participant

            Same thread would be the same TCL interp, true?

            Can I get a 30 second explanation (if possible) on how I could use namespaces?   Or a link on the interwebs where I can educate myself.

            Thanks in advance.

            David

          • January 4, 2016 at 11:55 pm #83500
            Charlie Bursell
            Participant

              Simply Google “tcl namespace tutorial” and you will see many.

            • January 5, 2016 at 3:46 pm #83501
              Terry Kellum
              Participant

                If you don’t have it already, I would highly recommend the Brent Welch book “Practical Programming in TCL and TK”.  I have the Fourth Edition.

                http://www.amazon.com/Practical-Programming-Tcl-Tk-4th/dp/0130385603

                ISBN 0-13-038560-3

                There is a whole chapter on Namespaces.

                A quick sketch on namespaces with regard to your variable issue is that namespaces provide a hierarchical set of global variable references.

                Say we wanted a variable named “common”.  We can put that variable in a namespace for access by any proc that runs in that interpreter.

                (In Cloverleaf, each UPOC in an engine has a common interpreter.)

                You initialize by using the incantation:

                Code:

                namespace eval MySpace {
                  variable common
                }

                You can then use the global variable in any of the procs that run in that UPOC thusly,

                Code:

                set MySpace::common  “MyScalar”

                puts $MySpace::common

                You can also create procs in namespaces and call them from any downstream proc as well.  They are an indispensable utility for advanced implementation.

                I realize that this involves renaming variables, but using namespaces is well worth the investment.

              • January 5, 2016 at 7:21 pm #83502
                David Barr
                Participant

                  Can you use message metadata (the USERDATA field) instead of global variables to pass data to the other procs? This would be a lot cleaner.

                • January 5, 2016 at 7:55 pm #83503
                  Terry Kellum
                  Participant

                    You have to.  The interpreters are vertical, not horizontal.

                    If you want extra-data to go with the message, you have to use metadata fields.  I have used USERDATA before to carry information across the translate to the post-procs.

                  • January 6, 2016 at 8:10 pm #83504
                    David Coffey
                    Participant

                      Thank you to everyone who responded to my question.  

                      In retrospect it is not that complex, though it did take me some time to get to a working model.

                      David

                    • February 10, 2016 at 3:41 pm #83505
                      Anwar Husain
                      Participant

                        I used global associative arrays to store values, for dynamic declaration and assignment.

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