16 User settable defaults

16.1 What’s the pattern?

It’s sometimes useful to give the user control over default values, so that they can set once per session or once for every session in their .Rprofile. To do so, use getOption() in the default value.

Note that this pattern should general only be used to control the side-effects of a function, not its compute value. The two primary uses are for controlling the appearance of output, particularly in print() methods, and for setting default values in generated templates.

Related patterns:

  • If a global option affects the results of the computation (not just its side-effects), you have an example of Chapter 6.

16.2 What are some examples?

16.3 Why is it important?

16.4 What are the exceptions?

16.5 How do I use it?