Classes vs. Functions

Question

Functions are easy to understand even for someone without any programming experience, but with a fair math background. On the other hand, classes seem to be more difficult to grasp.

Let's say I want to make a class/function that calculates the age of a person given his/her birthday year and the current year. Should I create a class for this, or a function? Or is the choice dependant to the scenario?

P.S. I am working on Python, but I guess the question is generic.

Answer 1

i know it is a controversial topic, and likely i get burned now. but here are my thoughts.

For myself i figured that it is best to avoid classes as long as possible. If i need a complex datatype I use simple struct (C/C++), dict (python), JSON (js), or similar, i.e. no constructor, no class methods, no operator overloading, no inheritance, etc. When using class, you can get carried away by OOP itself (What Design pattern, what should be private, bla bla), and loose focus on the essential stuff you wanted to code in the first place.

If your project grows big and messy, then OOP starts to make sense because some sort of helicopter-view system architecture is needed. "function vs class" also depends on the task ahead of you.

function

• purpose: process data, manipulate data, create result sets.
• when to use: always code a function if you want to do this: “y=f(x)”

struct/dict/json/etc (instead of class)

• purpose: store attr./param., maintain attr./param., reuse attr./param., use attr./param. later.
• when to use: if you deal with a set of attributes/params (preferably not mutable)
• different languages same thing: struct (C/C++), JSON (js), dict (python), etc.
• always prefer simple struct/dict/json/etc over complicated classes (keep it simple!)

class (if it is a new data type)

• a simple perspective: is a struct (C), dict (python), json (js), etc. with methods attached.
• The method should only make sense in combination with the data/param stored in the class.
• my advice: never code complex stuff inside class methods (call an external function instead)
• warning: do not misuse classes as fake namespace for functions! (this happens very often!)
• other use cases: if you want to do a lot of operator overloading then use classes (e.g. your own matrix/vector multiplication class)
• ask yourself: is it really a new “data type”? (Yes => class | No => can you avoid using a class)

array/vector/list (to store a lot of data)

• purpose: store a lot of homogeneous data of the same data type, e.g. time series
• advice#1: just use what your programming language already have. do not reinvent it
• advice#2: if you really want your “class mysupercooldatacontainer”, then overload an existing array/vector/list/etc class (e.g. “class mycontainer : public std::vector…”)

enum (enum class)

• i just mention it
• advice#1: use enum plus switch-case instead of overcomplicated OOP design patterns
• advice#2: use finite state machines

Answer 2

I'm going to break from the herd on this one and provide an alternate point of view:

Never create classes.

Reliance on classes has a significant tendency to cause coders to create bloated and slow code. Classes getting passed around (since they're objects) take a lot more computational power than calling a function and passing a string or two. Proper naming conventions on functions can do pretty much everything creating a class can do, and with only a fraction of the overhead and better code readability.

That doesn't mean you shouldn't learn to understand classes though. If you're coding with others, people will use them all the time and you'll need to know how to juggle those classes. Writing your code to rely on functions means the code will be smaller, faster, and more readable. I've seen huge sites written using only functions that were snappy and quick, and I've seen tiny sites that had minimal functionality that relied heavily on classes and broke constantly. (When you have classes extending classes that contain classes as part of their classes, you know you've lost all semblance of easy maintainability.)

When it comes down to it, all data you're going to want to pass can easily be handled by the existing datatypes.

Classes were created as a mental crutch and provide no actual extra functionality, and the overly-complicated code they have a tendency to create defeats the point of that crutch in the long run.