Erlang Programming

Chapter 7. Records and Macros

As soon as your first Erlang product reaches the market and is deployed around the world, you start working on feature enhancements for the second release. Imagine 15,000 lines of code, which incidentally happens to be the size of the code base of the first Erlang product Ericsson shipped, the Mobility Server. In your code base, you have tuples that contain data relating to the existing features and constants that have been hardcoded. When you add new features, you need to add fields to these tuples. The problem is that the fields need to be updated not only in the code base where you are adding these features, but also in the remaining 15,000 lines of code where you aren’t adding them. Missing one tuple will cause a runtime error. Assuming your constants also need to be updated, you need to change the hardcoded values everywhere they are used. And even more costly than implementing these software changes is the fact that the entire code base needs to be retested to ensure that no new bugs have been introduced or fields and constant updates have been omitted.

One of the most common constructions in computing is to bring together a number of pieces of data as a single item. Erlang tuples provide the basic mechanism for collecting data, but they do have some disadvantages, particularly when a larger number of data items are collected as a single object. In the first part of this chapter, you will learn about records, which overcome most of these disadvantages ...