Global values

Apart from variable and type declarations, Rust also allows us to define global values that can be accessed from anywhere in the program. They follow the naming convention of every letter being uppercase. These are of two kinds: constants and statics. There are also constant functions, which can be called to initialize these global values. Let's explore constants first.

 

Constants

The first form of global values are constants. Here's how we can define one:

// constants.rs

const HEADER: &'static [u8; 4] = b"Obj\0"; 

fn main() {
    println!("{:?}", HEADER);
}

We use the const keyword to create constants. As constants aren't declared with the let keyword, specifying types is a must when creating them. Now, we can use HEADER where we would use the byte literal, Obj\.  b"" is a convenient syntax to create a sequence of bytes of the &'static [u8; n] type, as in a 'static reference to a fixed-sized array of bytes. Constants represent concrete values and don't have any memory...