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

// constants.rs

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

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 location associated with them. They are inlined wherever they are used.