同时优化和可测试性 - 如何将代码分解为更小的单元

Question

I am trying to break up a long "main" program in order to be able to modify it, and also perhaps to unit-test it. It uses some huge data, so I hesitate:

What is best: to have function calls, with possibly extremely large (memory-wise) data being passed,

(a) by value, or

(b) by reference

(by extremely large, I mean maps and vectors of vectors of some structures and small classes... even images... that can be really large)

(c) Or to have private data that all the functions can access ? That may also mean that main_processing() or something could have a vector of all of them, while some functions will only have an item... With the advantage of functions being testable.

My question though has to do with optimization, while I am trying to break this monster into baby monsters, I also do not want to run out of memory.

It is not very clear to me how many copies of data I am going to have, if I create local variables.

Could someone please explain ?

Edit: this is not a generic "how to break down a very large program into classes". This program is part of a large solution, that is already broken down into small entities.

The executable I am looking at, while fairly large, is a single entity, with non-divisible data. So the data will either be all created as member variable in a single class, which I have already created, or it will (all of it) be passed around as argument around functions.

Which is better ?

Answer 1

If you want unit testing, you cannot "have private data that all the functions can access" because then, all of that data would be a part of each test case.

So, you must think about each function, and define exactly on which part of the data it works. As for function parameters and return values, it's very simple: use pass-by-value for small objects, and pass-by-reference for large objects.

You can use a guesstimate for the threshold that separates small and large. I use the rule "8 is small, anything more is large" but what is good for my system cannot be equally good for yours.

Answer 2

This seems more like a general question about OOP. Split up your data into logically grouped concepts (classes), and place the code that works with those data elements with the data (member functions), then tie it all together with composition, inheritance, etc.

Your question is too broad to give more specific advice.