A concurrent data structure, is a data structure (e.g. list, stack) that can be used by multiple threads concurently and it will always show a consistent state to each thread.

Consistency

The definition above mentions that the data structure will always show a consistent state. To understand this, let’s analyze a data structure that is not concurrent and can end in an inconsistent state.

Let’s say we are building an application that draws a single rectangle. The dimensions of this rectangle can be modified by users around the world, they just need to visit a website and enter the new dimensions.

A few days ago I was looking at some code and I found something I didn’t understand. It looked something like this:

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void someFunction(int SomeClass::*value) {
  ...

I had never seen and * used after ::, so I had to do some research to find what that means. It turns out that is a pointer to a class member. In this post I’m going to explain how these work and when they might be useful.

Pointers to members

Pointers to members are pretty uncommon, so it will be very rarely that you will need to use them.

Operators are a fundamental part of programming languages. They allow us to perform operations on operands by using a symbol. If you have ever written code, you probably know what this snippet does:

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int a = 3 + 1;

Variable a will be initialized to 4. It is initialized to this value, because the + operator has been used to add the values of 3 and 1. The = sign, is also an operator that assigns the value of the addition to the variable a.

We use these operators without thinking too much about them, but they are just symbols that perform a certain action, like any function we could define.

It turns out we can override the behavior of an existing operator. That’s what this article will focus on.

As part of getting a new computer, I want to be able to run a script to configure gnome terminal to my preferred setup. Doing this is not very hard, but finding how to do it took me some time.

The first thing we need to do is get the default terminal profile id:

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$ gsettings get org.gnome.Terminal.ProfilesList default
'b1dcc9dd-5262-4d8d-a863-c897e6d979b9'

In C++, all expressions have two properies: a type and a value category. Value categories are a little complicated to understand and have gone through a few changes with time.

lvalue and rvalue

Lvalue stands for locator value. An lvalue is something that occupies a memory location. But… doesn’t everything occupy a memory location? Not necessarily. Let’s look at a simple expression:

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int number = 7;

In this post I’m going to write about using exceptions for error handling in C++.

Exceptions

They are called exceptions, because they happen in exceptional scenarios. A program should in most cases run without exceptions, but sometimes unexpected things happen and we might want to do something in those scenarios.

Exceptions happen when there is either a developer error (Dereferencing a null pointer) or an environment error (Trying to write to a disk that is full). They should not happen for user triggered errors (incorrect input by user), if those errors are common.

When an error such as dereferencing a null pointer occurs, an Exception object is created. The Exception object contains information about the error, and the state of the program at the time this happened. The exception will then be thrown and left for the runtime to handle.

After installing a new distribution in my computer, I usually want to make some tweaks to gnome. In this post I’m going to explain how to do these tweaks from the command line, so they can be scripted.

gsettings

Gsettings is a command-line tools that allows us to modify gnome settings. To modify a setting we can use the set command. The format is like the following:

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gsettings set SCHEMA[:PATH] KEY VALUE

Ubuntu recently introduced snaps. Snaps are a new way of packaging applications in a way that there will be no dependency conflicts (because all dependencies are included). The only problem is that Ubuntu will create a snap folder in your home folder that you will most likely never need to access.

If you, like me, find this folder annoying, you can hide it from Nautilus:

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cd ~
echo snap >> ~/.hidden

This makes the folder invisible in Nautilus, but it will still be visible in other places (The terminal, for example).

I reinstalled Ubuntu on my personal computer recently and I noticed that there are some things I don’t like about the default distribution. One of the things I noticed is that Firefox keeps asking me if I want it to remember my passwords, which I don’t.

I know that I can go to settings and disable this feature, but I wanted to learn how to do it programmatically, so in the future I can just run a script and have Firefox work the way I want.

Preferences

There is documentation explaining how preferences work for mozilla projects, but it’s a little hard to understand how to exactly do what I wanted to do.

If you are not familiar with Inheritance, I recommend you read my short article about inheritance first.

One of the features of Object Oriented Programming is Polymorphism. Virtual functions in C++ allow developers to achieve run-time polymorphism by overwriting methods of a base class.

In my article about inheritance, I showed how we can create classes that inherit from a base (or parent) class. Something similar to the following:

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class Greeter {
 public:
  void talk() {
    std::cout << "hello" << std::endl;
  }
};

class SpanishGreeter : public Greeter {
 public:
  void talk() {
    std::cout << "hola" << std::endl;
  }
};