Example code and snippets are quite suited to the role they play in a book such as this: highlighting the usage of a language feature in the context of an explanation about that feature. What they aren't ideal for is showing the big picture, or reinforcing how all the disparate language features work together. That role is best played by a sample project that is developed over the course of the book.
In deciding what sort of program to develop as the sample project, I had a few goals in mind. Most importantly, it should be easy for the reader to follow, shouldn't be too time-consuming to implement, shouldn't have any third-party library dependencies, and should serve as a demonstration of as many D features as possible. I finally settled on something that I think fits each requirement to some degree. Few readers will find it immediately useful in its final form, but that's no problem. A practical post-book D project is to modify or extend the sample to tailor it to a specific, customized use case.
A few months before I started on this book, my wife and I moved house. Though I rarely buy new DVDs these days, I've assembled a modest collection of them over the years. I was more than a little obsessive about keeping them in their original cases, so I kept them lined up on a number of shelves, loosely organized around genre or leading actor/actress. That is just untenable in the long run. They take up too much space and they're a pain to pack when relocating. Even so, I'm reluctant to rip them to cloud storage and throw them all out. Motivated by the move, I bought several multi-disc cases (the kind with a zipper on the outside and several CD/DVD sleeves on the inside) and transferred each disc from its original case into one of the new ones.
This was something I just wanted to get done, so I only made a meager effort to organize the cases. The result is that it's no easy thing to find a particular DVD. Since the move, I've had it in the back of my mind to whip up a program I can use to organize things, but I've continually put it off as it isn't a big priority. This book is the perfect excuse to get it done. So you and I are going to create a program that can allow me to organize my DVDs. I'm going to call it MovieMan (for Movie Manager) because that sounds much better to me than DVDMan.
We're going to develop two versions of the program. In order to keep the size and complexity of the program manageable, the first version will be a command-line program with a limited number of features. The user will be able to:
- Enter a movie title, a case ID, and a page (sleeve) number
- Find and display movies by title
- List all movies in a given case
- List all movies on a given page of a given case
- List all movies
We'll implement this first version piece by piece, adding new functionality as we learn about the language features we'll use to implement it. We'll complete the program in Chapter 7, Composing Functional Pipelines with Algorithms and Ranges.
In Chapter 10, Taking D Online, we'll spend the entire chapter developing a different version of the program as a web application using a library called vibe.d. The purpose of this version isn't to demonstrate language features, but to show how to develop web apps with vibe.d. We'll relax our requirement about third-party libraries (vibe.d is a library, after all) and make use of a database API to store the movie data. We'll also add support for editing movies and deleting them from the database. By the end of the book, you'll have two fairly simple programs that illustrate how several D features work together.