Using Modules to Reuse and Organize Code
When you start writing programs in Rust, your code might live solely in the
main function. As your code grows, you’ll eventually move functionality into
other functions for reuse and better organization. By splitting your code into
smaller chunks, each chunk is easier to understand on its own. But what happens
if you have too many functions? Rust has a module system that enables the reuse
of code in an organized fashion.
In the same way that you extract lines of code into a function, you can extract functions (and other code, like structs and enums) into different modules. A module is a namespace that contains definitions of functions or types, and you can choose whether those definitions are visible outside their module (public) or not (private). Here’s an overview of how modules work:
modkeyword declares a new module. Code within the module appears either immediately following this declaration within curly brackets or in another file.
- By default, functions, types, constants, and modules are private. The
pubkeyword makes an item public and therefore visible outside its namespace.
usekeyword brings modules, or the definitions inside modules, into scope so it’s easier to refer to them.
We’ll look at each of these parts to see how they fit into the whole.