So a callback is a call to a program, but the program called is variable. As in the example of an exit program the callback is a configuration option. We configure the system to call a program as opposed to having a hardcoded program name. Is this the essence of a callback?


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Scott Klement
Sent: Monday, October 15, 2012 5:05 PM
To: Midrange Systems Technical Discussion
Subject: Re: Callback

Hi Richard,

Callbacks are extremely commonplace in computer programming. I'm kinda shocked at seeing not one but multiple people in this thread saying that they don't even know what a callback is.

Exit programs are an example of a callback. You give the system the name of a program, and it calls it at a particular time.

Triggers are another.

The %HANDLER routines used by XML-SAX or XML-INTO are callbacks.

APIs like Qp0lProcessSubtree(), QaneSava, QaneRsta use callbacks.

I use callbacks in RPG, C, Java, JavaScript. In fact, in JavaScript they are utterly ubiquitous, you can't sneeze without using a callback in JavaScript.

You should definitely take the time to learn about them.

On 10/15/2012 3:50 PM, Richard Reeve wrote:
Has anyone ever heard of a callback as it is related to the IBM i? I was asked to explain a callback during an interview and I'd never even heard of it. Can any of you explain to me what a callback is and how it is used? I tried google but didn't get a good explanation.


Warmest Regards,

Richard Reeve

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