What's the difference between data and code?

Question

To take an example, consider a set of discounts available to a supermarket shopper.

We could define these rules as data in some standard fashion (lists of qualifyin

Answer 1

The important note is that you want to separate out the part of your code that will execute the same every time, (i.e. applying a discount) from the part of your code which could change (i.e. the products to be discounted, or the % of the discount, etc.)

This is simply for safety. If a discount changes, you won't have to re-write your discount code, you'll only need to go into your discounts repository (DB, or app file, or xml file, or however you choose to implement it) and make a small change to a number.

Also, if the discount code is separated into an XML file, then you can give the entire application to a manager, and with sufficient instructions, they won't need to pester you whenever they want to change the discount rates.

When you mix in data and code, you are exponentially increasing the odds of breaking when anything changes. So, as leppie said, you need to extract the constantly changing parts, and put them in a separate place.