This is a usefull pattern on Rust match
when you want to match slices of a vector.
Imagine this problem: We want to implement a function which takes an vector containing the names of people that like an item. It must return the display text as shown in the examples:
[] --> "no one likes this"
["Peter"] --> "Peter likes this"
["Jacob", "Alex"] --> "Jacob and Alex like this"
["Max", "John", "Mark"] --> "Max, John and Mark like this"
["Alex", "Jacob", "Mark", "Max"] --> "Alex, Jacob and 2 others like this"
We can solve this with:
fn likes(names: &[&str]) -> String {
match names {
[] => format!("no one likes this"),
[a] => format!("{} likes this", a),
[a, b] => format!("{} and {} like this", a, b),
[a, b, c] => format!("{}, {} and {} like this", a, b, c),
[a, b, rest @ ..] => format!("{}, {} and {} others like this", a, b, rest.len()),
}
}
Where rest @ ..
will catch all the rest of the vector items.
Another examples:
let arr = [1, 2, 3];
match arr {
[1, _, _] => "starts with one",
[a, b, c] => "starts with something else",
};
let v = vec![1, 2, 3];
match v[..] {
[a, b] => { /* this arm will not apply because the length doesn't match */ }
[a, b, c] => { /* this arm will apply */ }
_ => { /* this wildcard is required, since the length is not known statically */ }
};
fn foo(words: &[&str]) {
match words {
[] => println!("empty slice!"),
[one] => println!("one element: {:?}", one),
[one, two] => println!("two elements: {:?} {:?}", one, two),
_ => println!("I'm not sure how many elements!"),
}
}
fn foo(words: &[&str]) {
match words {
["Hello", "World", "!", ..] => println!("Hello World!"),
["Foo", "Bar", ..] => println!("Baz"),
rest => println!("{:?}", rest),
}
}
fn foo(words: &[&str]) {
match words {
// Ignore everything but the last element, which must be "!".
[.., "!"] => println!("!!!"),
// `start` is a slice of everything except the last element, which must be "z".
[start @ .., "z"] => println!("starts with: {:?}", start),
// `end` is a slice of everything but the first element, which must be "a".
["a", end @ ..] => println!("ends with: {:?}", end),
rest => println!("{:?}", rest),
}
}
refs: