Some last notes on Functions

Objectives

1. Understand function cohesion

Notes

• I amusing Dale chapter 4.
• A step is concrete if all implementation details are fully specified
  • a line of an algorithm that corresponds to a few lines of code.
• A step is abstract if some of the implementation details are unspecified.
  • A line of an algorithm that is probably best implemented as a function.
• A function is cohesive if
  • All the parts do one thing and are related.
  • All steps are either concrete or abstract but not both.
• Another definition is we can summarize the function in a good name.
• We would like to write cohesive functions.
• Dale suggests the following steps to writing cohesive functions
  • Think about how you will solve the problem and write down steps.
  • If a step is easy to implement in c++, it is concrete and you are done.
  • If the step is abstract turn it into a function.
• A good abstract function should read like an algorithm.
• Let's take a look at My Homework 3 Design with this in mind.
• In general, function should be
  • Cohesive
  • Small, 1-30 lines
  • Do not repeat code, build a sub function.
• That last statement is worth repeating
• Smaller functions are
  • Easier to read and understand
  • Therefore easier to debug
  • And easier to test
  • And easier to document
  • And easier to modify
• Consider functions like M&Ms or potato chips, not like a candy bar or a sandwich.
  • The more the better.
• Should I write a single line function?
  • There are times this might be appropriate, but rare
• Should I write a 100 line function?
  • Unless it is a single simple task NO
• Should I have functions call functions
  • If it is appropriate, yes.