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Chapter 7: High Quality Routines. By Raj Ramsaroop. What Is A Good Routine?. A routine is a: Function (C ++). Method (Java ). Procedure (Visual Basic ). Macro. A routine should have a single purpose. Example: A Bad Routine. Why Was That A Bad Routine?. Name: HandleStuff () .
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Chapter 7: High Quality Routines By Raj Ramsaroop
What Is A Good Routine? • A routine is a: • Function (C++). • Method (Java). • Procedure (Visual Basic). • Macro. • A routine should have a single purpose.
Why Was That ABad Routine? Name: HandleStuff(). Too many parameters. No logical ordering to parameters. Looks like it’s trying to do more than one task. Not logically laid out. Input variable is changed. Unused parameters.
Why/When Create A Routine? Biggest reason: reduce complexity. Minimize code, avoid duplicate code. Make your code more maintainable. Easier to read.
Why/When Create A Routine? Cont. • Avoid duplicate code. • Only need to check one place. • Avoid writing the same thing twice. • Similar code in different routines – split them up. • Hide sequences. • Keeps code simple. • E.g. if you get data from a user and data from a file, neither routine should depend on each other.
Why/When Create A Routine? Cont. • Improve portability. • Make your code independent of hardware/software, or the project you are working on. • Can be reused – enforces object-oriented concepts. • Simplify complicated boolean tests. • E.g. isVisible() • Details of the test are out of the way. • The name is descriptive. • Emphasizes it’s significance.
Can Code Sometimes Be Too Small For A Routine? • Depends: • If you keep repeating the same line. • One line of code can balloon into something bigger. • Makes code more readable.
Routine Cohesion • Cohesion refers to how closely the operations in the routine are related. • Ensures routines perform one task well – and nothing else. • Acceptable types of cohesion: • Functional cohesion – the best type, is when a routine performs only one function. • Sequential cohesion. • Communicational cohesion. • Temporal cohesion.
Unacceptable Types Of Cohesion • Procedural cohesion – operations that are in a specific order and are combined for that specific reason. • Logical cohesion – basically methods with big ‘if statements’ • Operations are not usually logically related. • Only time this would be acceptable would be something like an event handler. • Coincidental cohesion – if you have this it probably means you need to redesign your program!
Naming Routines Name can be as long as it needs to be – as long as it doesn’t sound silly! Make it descriptive. Avoiding meaningless verbs (e.g. processOutput(), calculateData()). Don’t differentiate functions solely by a number! Use what the function returns to name the function. E.g. customerId.next(), printer.isReady() To name a procedure, use a strong verb followed by an object. E.g. printReport(), calculateInvoice() Use opposites such as get/set, open/close, first/last etc
How Long Should A Routine Be? A line is a noncomment, nonblank line of code. Book suggests up to 200 lines. They can be as long as they need to be as long as you focus on cohesion.
Using Routine Parameters • Put parameters in “input-modify-output” order. • As opposed to randomly or alphabetically. • Implies a sequence of operations. • If several routines take similar parameters, put them in the same order. • Use all parameters. • Status and error variables go last. • Don’t use routine parameters as working variables. • Document the input variables (range, units, values that should never appear etc). • Limit number of parameters to 7. • Check parameter types (mismatched types etc).
When To Use A Function Or Procedure And Return Values A function is a routine that returns something. A procedure is a routine that does something, but does not return anything. You can combine the two. Return values should return an object, not a reference or pointer to local data.