To be able to understand where println! comes from, we need to take a brief look at the Rust Standard Library. If you're familiar with C, C++, or C# (or any of the other languages commonly used), you'll have used something like this:
#include <stdio.h> #include <stdlib> using System.Collections.Generic;
These are standard libraries that the compiler comes with, and which the developer can optionally include. They contain many useful procedures, functions, and methods, all designed to make development simpler so that you don't need to keep reinventing the wheel when you need to do a common task.
A similar system exists in Rust in the form of crates. The std crate contains the Rust Standard Library, and it is by default included in every other crate. This means that you can use functionality from there without extra steps.
The crates are further separated into module hierarchies, with a double colon :: being a separator for the paths. So, for...