Code Complete, 2nd Edition

Design at the Routine Level

The idea of cohesion was introduced in a paper by Wayne Stevens, Glenford Myers, and Larry Constantine (1974). Other more modern concepts, including abstraction and encapsulation, tend to yield more insight at the class level (and have, in fact, largely superceded cohesion at the class level), but cohesion is still alive and well as the workhorse design heuristic at the individual-routine level.

For routines, cohesion refers to how closely the operations in a routine are related. Some programmers prefer the term "strength": how strongly related are the operations in a routine? A function like Cosine() is perfectly cohesive because the whole routine is dedicated to performing one function. A function like CosineAndTan() ...