Is there a metric analogous to the McCabe Complexity measure to measure how cohesive a routine is and also how loosely (or tightly) coupled the routine is to other code in the same code base?
I think the metric you are looking for is LCOM4, although it applies more to classes.
Sonar explains it nicely here:
...metric : LCOM4 (Lack Of Cohesion Methods) to measure how cohesive classes are. Interpreting this metric is pretty simple as value 1 means that a class has only one responsibility (good) and value X means that a class has probably X responsibilities (bad) and should be refactored/split.
There is not any magic here, only common sense. Let’s take a simple example with class Driver. This class has two fields : Car and Brain, and five methods : drive(), goTo(), stop(), getAngry() and drinkCoffee(). Here is the dependency graph between those components. There are three blocks of related components, so LCOM4 = 3, so the class seems to have three different responsibilities and breaks the Single Responsibility Principle.
It's a great tool, if you can use it. :)
- Afferent coupling: Number of responsibilities
- Efferent coupling: Number of dependencies
- Instability: Ratio of efferent coupling to total coupling (Afferent + Efferent).
Instability is supported in various code metric tools.