fn main() {
    let mut a: [i8; 10] = [42; 10];
    a[5] = 0;
    println!("a: {a:?}");
This slide should take about 5 minutes.
  • A value of the array type [T; N] holds N (a compile-time constant) elements of the same type T. Note that the length of the array is part of its type, which means that [u8; 3] and [u8; 4] are considered two different types. Slices, which have a size determined at runtime, are covered later.

  • Try accessing an out-of-bounds array element. Array accesses are checked at runtime. Rust can usually optimize these checks away, and they can be avoided using unsafe Rust.

  • We can use literals to assign values to arrays.

  • The println! macro asks for the debug implementation with the ? format parameter: {} gives the default output, {:?} gives the debug output. Types such as integers and strings implement the default output, but arrays only implement the debug output. This means that we must use debug output here.

  • Adding #, eg {a:#?}, invokes a “pretty printing” format, which can be easier to read.