I prefer to keep the number of function arguments to four or fewer.
It sounds like the function "merges" a rounded rectangle it into some environment. The first thing that comes to mind is to separate the activity into two parts: defining the rectangle, and then merging it.
rr = roundedRectangle(width, height, cornerRadius)
environment.merge(rr, how, alignment, where)
If the cornerRadius has a convenient default (e.g. zero), then you could switch to:
rr = roundedRectangle(width, height).setCornerRadius(r)
If the number of options to merge increases, then you could create a parameter object for those:
mm = mergeMethod(position).setAlignment(topCenter).setBehavior(...)
This allows for a natural extension to other shapes. It would be poor practice to repeat the list of mergeMethod arguments once for every shape that could be created.
=== Dan's Addendum ===
When splitting actions in this way, it is important to avoid introducing undesirable order dependencies. Any values not specified when an instance is created should have useful defaults. If you remove the
cornerRadius argument from the
roundedRectangle constructor, you must set a useful default. It must be sensible to write either
rr = roundedRectangle(width, height) or
rr = roundedRectangle(width, height).setCornerRadius(...).