Constants In The Global Scope
Here's the previous example we used to demonstrate a constant.
fn main() {
const ALFA: i32 = 100;
println!("Alfa {ALFA}");
}The const and println!() statements are
between the { and } of the main() function.
The terminology used for this is to say
those statements are in the main()
function's "scope".
Scope is like a one-way wrapper where:
- Anything that's in a surround scope can be be accessed by what's inside the inner scope, but
- Anything inside the scope can't be accessed by anything outside of it.
The main() function's scope is clearly delimited by
the { and }. There's another scope surrounding it
in our program that's invisible. It's what's called the
"global" scope. It begins at the start of the source code
and goes all the way to the end encompassing everything
in between.
What this means is that we can move the assignment for our
ALFA constant above the definition of the main()
function like this:
SOURCE CODE
const ALFA: i32 = 100;
fn main() {
println!("Alfa {ALFA}");
}