上QQ阅读APP看书，第一时间看更新

How it works...

Let's go through the code to understand the execution flow.

cargo is described in depth in Chapter 2, Managing Projects with Cargo, in this book.

The initial snippet is generated when cargo new hello-world is executed in step 1. As a project of type binary, a main function is required and rustc will be looking for it. Upon calling cargo run, cargo orchestrates compilation (with rustc) and linking (msvc on Windows, cc on *nix) and runs the resultant binary via its entry point: the main function (step 5).

In the function we create in step 3, we write a series of print!/println!/eprintln! statements, which are Rust macros. These macros facilitate the writing to the standard output or standard error channels of a command-line application and include additional arguments. In fact, if arguments are missing, the compiler won't compile the program.

Rust's macros work directly on the syntax tree of the language, providing type safety and the ability to check the parameters and arguments. Therefore, they can be seen as a function call with a few special abilities—but more on that in Chapter 6, Expressing Yourself with Macros.

The various arguments and the template string are combined using formatters, a powerful way to add real variables to the output without the need of concatenations or similar workarounds. This will reduce the number of allocations, considerably improving performance and memory efficiency. There is a wide range of how to format data types; to understand it more deeply, check out Rust's excellent documentation (https://doc.rust-lang.org/std/fmt/).

The last step then shows the output that the various combinations produced.

We've successfully learned to work with the command line I/O. Now, let's move on to the next recipe.