c9f66fd425
This is the result of running `dprint fmt` after removing `src/` from
the list of excluded directories.
This also reformats the Rust code: we might want to tweak this a bit in
the future since some of the changes removes the hand-formatting. Of
course, this formatting can be seen as a mis-feature, so maybe this is
good overall.
Thanks to mdbook-i18n-helpers 0.2, the POT file is nearly unchanged
after this, meaning that all existing translations remain valid! A few
messages were changed because of stray whitespace characters:
msgid ""
"Slices always borrow from another object. In this example, `a` has to remain "
-"'alive' (in scope) for at least as long as our slice. "
+"'alive' (in scope) for at least as long as our slice."
msgstr ""
The formatting is enforced in CI and we will have to see how annoying
this is in practice for the many contributors. If it becomes annoying,
we should look into fixing dprint/check#11 so that `dprint` can annotate
the lines that need fixing directly, then I think we can consider more
strict formatting checks.
I added more customization to `rustfmt.toml`. This is to better emulate
the dense style used in the course:
- `max_width = 85` allows lines to take up the full width available in
our code blocks (when taking margins and the line numbers into account).
- `wrap_comments = true` ensures that we don't show very long comments
in the code examples. I edited some comments to shorten them and avoid
unnecessary line breaks — please trim other unnecessarily long comments
when you see them! Remember we're writing code for slides 😄
- `use_small_heuristics = "Max"` allows for things like struct literals
and if-statements to take up the full line width configured above.
The formatting settings apply to all our Rust code right now — I think
we could improve this with https://github.com/dprint/dprint/issues/711
which lets us add per-directory `dprint` configuration files. However,
the `inherit: true` setting is not yet implemented (as far as I can
tell), so a nested configuration file will have to copy most or all of
the top-level file.
2.5 KiB
minutes
| minutes |
|---|
| 10 |
Tuples and Arrays
Tuples and arrays are the first "compound" types we have seen. All elements of an array have the same type, while tuples can accommodate different types. Both types have a size fixed at compile time.
| 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:?}");
}
Tuple assignment and access:
fn main() {
let t: (i8, bool) = (7, true);
println!("t.0: {}", t.0);
println!("t.1: {}", t.1);
}
Key points:
Arrays:
-
A value of the array type
[T; N]holdsN(a compile-time constant) elements of the same typeT. 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.
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
voidthat can be familiar to you from other programming languages.
- You can think of it as