Creating the command line parser

I have to confess one thing: I'm a command-line type of guy. Yes, I know it is considered by some people as outdated, but I love doing work on the terminal. I am definitely more productive and if you are using Linux or macOS, you can combine tools to get the results that you want. That's the reason that we are going to add a command line parser for this project.

There are some things we need to implement in order to start creating the command line parser. One functionality that we are going to add is the possibility of setting a default currency, which will avoid user of our application always having to specify the base currency to perform currency conversions.

To do that, we are going to create an action, We have seen how actions work in Chapter 1, Implementing the Weather Application, but just to refresh our minds, actions are classes that can be bound to command line arguments to execute a certain task. These actions are called automatically when the argument...