Compound Types

TypesLiterals
Arrays[T; N][20, 30, 40], [0; 3]
Tuples(), (T,), (T1, T2), โ€ฆ(), ('x',), ('x', 1.2), โ€ฆ

Array assignment and access:

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

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

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 โ€œpretty printingโ€ 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 โ€œunit typeโ€. 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 weโ€™ll see in a future slide.

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

T is a generic type