Constants

There's another type of variable besides mutable and immutable. They're called "constants".

Constants are like immutable variables with a few extra criteria. We've covered enough to get the idea for the first three:

  1. They are defined using the const keyword instead of let
  2. The mut keyword can't be used when creating them
  3. Names should always be in UPPER_SNAKE_CASE by convention.

These next three criteria require some knowledge we haven't gotten to yet, We'll touch on them in the next few pages.

  1. Constants can be declared in global scope (which will see on the next page)
  2. They must have a type annotation (e.g. the i32 in the example below which is coming up).
  3. They must be set to something determined at compile time (which we'll also get to shortly)
fn main() {
  const ALFA: i32 = 100;
  println!("Alfa {ALFA}");
}

CODE RUNNER

TODO

  • Examine moving constants to a points after you've talked about scope and types. Probably that makes the most sense.