Compound Types

Array assignment and access:

1. fn main() {
2. let mut a: [i8; 10] = [42; 10];
3. a[5] = 0;
4. println!("a: {:?}", a);
5. }

Tuple assignment and access:

1. fn main() {
2. let t: (i8, bool) = (7, true);
3. println!("1st index: {}", t.0);
4. println!("2nd index: {}", t.1);
5. }

Key points:

Arrays:

• Arrays have elements of the same type, T, and length, N, which is a compile-time constant. 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.
• We can use literals to assign values to arrays.
• In the main function, the print statement asks for the debug implementation with the ? format parameter: {} gives the default output, {:?} gives the debug output. We could also have used {a} and {a:?} without specifying the value after the format string.
• Adding #, eg {a:#?}, invokes a “pretty printing” format, which can be easier to read.

Tuples:

• Like arrays, tuples have a fixed length.
• Tuples group together values of different types into a compound type.
• Fields of a tuple can be accessed by the period and the index of the value, e.g. t.0, t.1.

• The empty tuple () is also known as the “unit type”. It is both a type, and the only valid value of that type - that is to say both the type and its value are expressed as (). It is used to indicate, for example, that a function or expression has no return value, as we’ll see in a future slide.

• You can think of it as void that can be familiar to you from other programming languages.