Constants

Constants replace the old C-like system of defines that bytec used until Battlecode 2023, and are much easier to use (for instance, they're scoped like all other items!). They look like let definitions, but using const instead of let. The constant value is always inlined into use sites - this is the difference between a top-level let and const.

Warning! The value of a constant is essentially pasted at every use. Generally, a constant should have a value that is known at compile time; otherwise, it may be worse than it looks for performance, as the value is evaluated multiple times (just use let instead if computation is involved). Additionally, something like const C = getCurrentTime() is possible, and would have a different value each time it is used, which though convenient is not easily visible. Eventually the compiler is intended to check that constants have compile-time known values, but this has not yet been implemented, so be careful.

#![allow(unused)]
fn main() {
// Main.bt
const SOME_FLAG = true;
const SOME_CONST = 12;

fn someFunction() {
    // This if will disappear, since the value of SOME_FLAG is known at compile time
    if SOME_FLAG {
        // SOME_CONST will be replaced with the value 12 during compilation
        println("SOME_CONST = " + SOME_CONST);
    }
}
}

You can also override constants from the command line with -C<module>::<constant>=<value> - for this example: -CMain::SOME_FLAG=false -CMain::SOME_CONST=42. (This is an analogue of C's -DSOME_CONST=52.) This can be useful for testing different magic numbers and features in a systematic way.