Refactoring: Improving the Design of Existing Code (Addison-Wesley Signature Series (Fowler))

by Martin Fowler

One use of temporary variables is to capture the value of some code in order to refer to it later in a function. Using a temp allows me to refer to the value while explaining its meaning and avoiding repeating the code that calculates it. But while using a variable is handy, it can often be worthwhile to go a step further and use a function instead. If I’m working on breaking up a large function, turning variables into their own functions makes it easier to extract parts of the function, since I no longer need to pass in variables into the extracted functions. Putting this logic into functions often also sets up a stronger boundary between the extracted logic and the original function, which helps me spot and avoid awkward dependencies and side effects. Using functions instead of variables also allows me to avoid duplicating the calculation logic in similar functions. Whenever I see variables calculated in the same way in different places, I look to turn them into a single function.