Category Archives: C++

Stop using bool in C++ for function parameters !

Introduction

This article deals with the use of bool in C++. Should we use it or not? That is the question we will try to answer here. However, this is more of an open discussion than a coding rule.

First of all, what is the bool type? A boolean variable is a variable that can be set to false or true.

Imagine you have a simple function to decide whether or not to buy an house, you may design it like this

Problems arrived!

Then, when you want to use it, you can do it like this:

There is no problem here, however the reader may not understand at first glance if the false means no pools, or if it means no energy saving lights.

So, you will try to change the function call like this:

Now you are happy, the reader knows exactly what bool means. Are you sure? A very thorough reader may notice that there is a reversal of the parameters.

How to solve the problem?

There is different ways to solve this type of problem. The first is to use a strong_type. There are many libraries that offer this kind of thing, however, a simple enum class can do the trick.

Not only will the reader know which argument corresponds to which parameter, but also, in the case of a parameter inversion, the compiler will not let the error pass

Let’s rewrite the function declaration:

Conclusion

I would encourage people not to use the bool type for function parameters. What do you think? Do you use bool everywhere?

Thanks for reading !

Thoughts about getters and setters in C++

This article deals with getters and setters in C++. I am sorry, it is not about coroutine, but part 2 of thread pools will come in the following weeks.

TL;DR: Getters and setters are bad for structure like objects.

Introduction

In this article, I will only give my opinion about them, I don’t want to offend anyone, I am just going to explain why, or why not, use getters and setters. I would be glad to have any debates in the comments part.

Just to be clear about what I am talking about when I talk about getter, I talk about a function that just returns something, and when I talk about setter, I talk about a function that just modifies one internal value, not doing any verification or other computations.

Getter performances

Let’s say we have a simple structure with their usual getter and setters:

Let’s compare this version with the one without getters and setters.

It is incredibly shorter and less error_prone. We can not make the error to return the last name instead of the first name.

Both codes are fully functional. We have a class Person with the first name, the last name, and an age. However, let’s say we want a function that returns the presentation of a person.

Show the performance differences between computation using getters by value and public access.

The version without getters performs this task 30% quicker than the version with getters. But why? It is because of the return by value of the getters functions. Returning by value makes a copy that results in poorer performance. Let’s compare the performance between person.getFirstName(); and person.firstName.

Show the performance differences between getters by value and public access.

As you can see, accessing directly the first name instead of a getter is equivalent to a noop.

Getter by const reference

However, it is possible to not return by value but return by reference instead. Going that way, we will have the same performance as without getters. The new code will look like that

Since we get the same performance as before, are we done? To answer this question, you can try to execute this code.

You may see some weird characters wrote in the console. But why? What happened when you do make().getLastName()?

  1. You create a Person
  2. You get a reference to the last name
  3. You delete Person

You have a dangling reference! It can lead to a crash (in the best case) or something worst than what can be found in a horror movie.

To deal with such a thing, we must introduce reference qualified functions.

Here is the new solution that works everywhere. You need 2 getters. One for lvalue and one for rvalue (both xvalue and prvalue).

Setter issues

There is not a lot to say in this section. If you want to achieve the best performances, you must write a setter that takes a lvalue and one that takes a rvalue. However, it is generally fine to just have a setter that takes a value that will be moved. Nevertheless, you have to pay the price of an extra move. However, that way, you cannot just make a little enhancement. You must replace the whole variable. If you just wanted to replace one A by a D in a name, it will not be possible by using setters. However, using direct access makes it possible.

What about immutable variables?

Ones will tell you to just make the member attribute as const. However, I am not ok with this solution. Indeed, making it const will prevent the move semantic and will lead to unnecessary copy.

I have no magic solution to propose you right now. Nevertheless, we can write a wrapper which we can named immutable<T>. This wrapper must be able to be :

  1. Constructible
  2. Since it is immutable, it must not be assignable
  3. It can be copy constructible or move constructible
  4. It must be convertible to const T& when being a lvalue
  5. It must be convertible to T when being a rvalue
  6. It must be used like other wrapper through operator* or operator->.
  7. It must be easy to get the address of the underlying object.

Here is a little implementation

So, for an immutable Person, you can just write:

Conclusion

I would not say that getters and setters are bad. However, when you do not need to do anything else in your getter and your setter, achieving the best performance, safety and flexibility lead to writing:

  • 3 getters (or even 4): const lvalue, rvalue, const rvalue, and if you want, non-const lvalue (even if sounds really weird since it is easier to just use direct access)
  • 1 setter (or 2 if you want to have the maximum performance)

It is a lot of boilerplate for almost anything.

Some people will tell you that getters and setters enforce encapsulation, but they don’t. Encapsulation is not just making attributes private. It is about hiding things from users, and for structure-like objects, you rarely want to hide anything.

My advice is: when you have a structure like objects, just don’t use getter and setters and go with public / direct access. To be simple, if your setter does not enforce any invariant, you don’t need a private attribute.

PS: For people who use libraries using shallow copy, the performance impact is less important. However, you still need to write 2 functions instead of 0. Don’t forget, the less code you write, the less bugged it will be, easier to maintain, and easier to read.

And you ? Do you use getters and setters? And why?