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I am working on a C++ project, where the lead is saying that private/public doesn't matter in practice, and so that all the classes should have only public members. Basically, he wants C++ with struct only.
His main argument is that huge code bases were written in C without private, and no bugs would have been prevented in those code bases by having a private keyword, so why bother?
I am countering by saying that private state is cleaner modularization, that it makes the code easier to reason about, easier to test, easier to refactor, that I could write assertions to make assumptions explicit with private state, that different teams could work independently by just agreeing on the interface of classes, but nothing seems to convince him.
What are the purely technical/objective arguments in this discussion, for/against struct/class with private members? It is a given that there is no generic answer, but I would like to list all the objective arguments I could use to evaluate which one to use in any given situation. Something like reasonable guidelines that we could all agree on, or an analysis grid that would tell us which one to use, given parameters of the situation. I would like to steer clear from personal preferences, as discussion of personal preferences is probably not productive.
It would be particularly useful to see a few concrete examples that demonstrate the pros/cons of each in specific situations.
My answer would be, "No, there is nothing to add." As you said, he has already dismissed good reasons. Maybe he's pleased with himself for recognizing that code can work without any private members, so he's being stubborn. I don't know.
A struct is fine where it makes sense, but people (like me) who have maintained code extensively know that encapsulation does improve design.
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I keep seeing code where class variables are declared after methods at the bottom like
class Observer
{
public:
int getstate();
void update(int state);
private:
int state;
};
Is this a common practice I should adapt to? Is there a reason for ordering them like this?
It is a commonly used way to structure the code but it is not mandated by the language. You are free to format your code as you wish. The most important thing to remember is:
Code is written for people, not for machines.
Keep that in mind and put yourself in the shoes of the next person who will be reading your code. It should be crystal clear.
Is this a common practice I should adapt to? Is there a reason for ordering them like this?
You don't have to. Either order works. The choice is subjective. I don't think there's a significant reason to prefer one order over the other myself.
However, I do recommend ordering public members - whether variables or functions - before protected and those before private. This is because public interface of the class is more likely to be important to a programmer who reads the class definition. Ordering the important parts first potentially reduces the time that the reader has to spend to find what they're looking for.
I also recommend getting used to a variety of different orders, as each programmer has their own preferences and there won't be consitency between different projects, nor even necessarily within a project.
Most people choose to put public first because developers and editors generally need the more important information. It also makes the code easier and clearer.
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Many times I hear "Singleton is a bad practice, static methods are bad practice" all I can see for reason is "hard to test".
But I do think sometimes its really good if an operation can be done without instantiate a class.
EDIT: just because of testing, anyone can find out that "private methods are bad too, they cant be tested" for example
It is a question about semantics and expressing intent.
A static method is not inherently bad, apart from that it is hard to test. The bad part is confusing other programmers by using static methods just to avoid creating new instances.
If the method relates to the class itself and not to individual instances (Like a factory method for example), then by all means use a static one. But if the method semantically belongs to an individual instance, then use a non static method.
Static methods are generally frowned upon for much the same reason as global variables, in addition to testing issues:
Static methods do not relate to a specific class instance so will not always be thread safe.
Systems with lots of statics methods often do not scale well.
Confusion due to the mixture between calling static methods of a class and members of an instance of a class can lead to maintenance issues.
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It seems to me that C++-style struct can do more things than a C-style struct (for example, you can have member functions and access specifiers). What's the design reason for this, considering we already have class in c++?
A real design example would be appreciated.
What's the design reason for this, considering we already have class in c++?
A few potential benefits I can image are:
Easier compiler implementation by being able to handle structs and classes in almost the same way.
More options for developers. For instance, being able to use structs as more than just POD types by adding basic things like constructors, while leaving classes for usages where for object-oriented design is used.
Being able to derive from structs in C-compatible headers of 3rd-party libraries to add on convenience features like constructors and member functions.
A real design example would be appreciated.
Using the third idea: The Windows headers define a struct called RECT. MFC provides a class CRect which derives from it and provides several useful methods, but it's still able to be used in place of a RECT whenever needed by the Windows API.
If you are asking for a "design reason" to allow members to be defaulted to public visibility, then this is easily justified: The legacy struct from C originally assumed all members were public, so defaulting to public would make it easier to port C code to C++ without heavy modifications to the original C code. It also makes it easier to share C header files with C++ code.
If you are asking why struct was extended in C++ to be allowed to have protected/private sections and methods, then this has more to do with what the inventor of C++ imagined to be the fundamental difference between a struct and a class from the point of view of a user of the language. The answer was ultimately made that fundamentally, there is really no difference whatsoever (save the default to public visibility).
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I have a project that contains several classes. I added to this project several functions that are used by one of the classes, let named MainClass. I put all these functions in a file stuff.h. To use these functions I include the stuff.h file at the beginning of the implementation of the class MainClass. I am wondering if this is a good style of programming or if it would be better to create a new class and add my functions to this class. Then I instantiate this class in the MainClass.
Not so good style. Starting from the fact headers are not actually intended to have real code but declarations of things defined somewhere else.
If your 'external' functions are used only by MainClass why not to do them class methods? Even maybe private so they are only visible inside class? Keep things as encapsulated as you can. If you're trying to follow C++, try not to use 'plain C functions'. It's different language. If you absolutely need plain routines, use namespaces instead. But please try to keep your code inside modules (.cpp), not in headers.
Regarding other classes. It depends if you know why you need other classes. If you don't know why, you don't need them. BTW OOP is not always 'best' approach, especially in things like balance between inheritance and composition. You should understand what you really want to achieve to select proper technique.
Indeed you need good C++ book. Chapters about project composition, compilation process, translation units so you will understand logics behind this. This Q&A site cannot explain you everything. Just give some points.
Good question here for you
I think it would be better to create a new class, or several new classes that are ordered by the different ways the functions will be used. That's more in line with classic OO.
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So, in the process of taking a data-structures class (in C++), my professor wanted us to manipulate a linked list of playing cards. That doesn't matter however, what I am interested in is why she did not use an enumerator to represent the suites.
In her code, she used strings to hold the suite of a card. This seemed inefficient because she wanted us to sort them based on suite, under the circumstances, it would have been considerably easier if she had used an enumerated type instead of a string. The string did not offer any help either, because in printing the suite, she output a Unicode character, roughly doubling the length of her function, simply because she did not use an enum.
Is there any reason for her to have done this, or does she simply have strange preferences when it comes to code style?
If you really want to know what your professor's reasoning is, you have to ask your professor. I can only speculate.
But if I were to speculate, I would guess that there are two possible reasons why your professor chose to use strings as descriptors for these attributes.
She is trying to keep the code simple and easy for newbie C++ programmers to understand. Whether the means meet the goal is debateable.
(Personal bias alert) Professors and others in academia, with no real-world experience, often do and teach things that I would consider to be highly sub-optimal.
My guess would be that she either had not considered that approach or that she wanted to test your ability to work with sorting strings.
Code examples might help in that they might clarify what she did and what you think she should have done.
The likely answer is that she just didn't think about the problem she was using to demonstrate whatever she is trying to teach you. That is, she wanted you to focus on sorting (for example), and probably took some code written by someone else and just adapted it to that purpose without much thought.