rust Compound Types

Compound Types

	Types	Literals
Arrays	[T; N]	[20, 30, 40], [0; 3]
Tuples	(), (T,), (T1, T2), …	(), (‘x’,), (‘x’, 1.2), …

Array assignment and access:

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

a: [42, 42, 42, 42, 42, 0, 42, 42, 42, 42]

Tuple assignment and access:

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

1st index: 7
2nd index: true

Notes: Arrays:

• 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.
• 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.