Best explanation I have seen of indirection. Thanks,
thurman > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:hardhats- > [EMAIL PROTECTED] On Behalf Of Gregory Woodhouse > Sent: Wednesday, August 24, 2005 8:04 PM > To: hardhats-members@lists.sourceforge.net > Subject: Re: [Hardhats-members] All about programming > > Well, indirection is not a concept unique to MUMPS. Do you recall > that I said the symbol table associates a memory location with a > variable. Well, that memory location is identified by a (typically > large) integer. Indirection is the process of retrieving the value > stored at that location. In C, if n is an integer variable, &n will > be the location where it is stored, and if p is pointer to that > memory location, *p is the value stored there. The * operation is > called indirection. Another term you will often hear is dereferencing > the pointer. > > Now, MUMPS doesn't have pointers, but you can use a variable to store > the name (or part of the name) of another variable, or even a > command. As a simple case, try the following > > SET X="HELLO" > SET Y="X" > WRITE @Y > > The @ operator is the indirection operator in MUMPS. What this code > does is lookup the value of Y to get "X" and then lookup the value of > X to get "HELLO". > > Indirection is a very powerful technique allowing you to implement > things like callbacks (where you basically say to a function "execute > this code if something special happens") and dynamic dispatch tables > (where you basically create a table containing code that should be > called in certain situations). It is a very powerful technique and > especially useful when you're trying to design generic tools. > > === > Gregory Woodhouse > [EMAIL PROTECTED] > > "Perfection is achieved, not when there is nothing more to add, but > when there is nothing left to take away." > -- Antoine de Saint-Exupery > > On Aug 24, 2005, at 5:07 PM, Nancy Anthracite wrote: > > > And to think I bothered to buy some books. ;-) > > > > Please tell me about indirection. That is the one thing I hear > > newish MUMPS > > programmers saying they want to know more about. > > > > ------------------------------------------------------- > SF.Net email is Sponsored by the Better Software Conference & EXPO > September 19-22, 2005 * San Francisco, CA * Development Lifecycle > Practices > Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA > Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf > _______________________________________________ > Hardhats-members mailing list > Hardhats-members@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/hardhats-members ------------------------------------------------------- SF.Net email is Sponsored by the Better Software Conference & EXPO September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf _______________________________________________ Hardhats-members mailing list Hardhats-members@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/hardhats-members
