Rust
Summary - Advanced patterns
Combine struct, @ and guard to build a color classifier.
Advanced pattern matching summary
Patterns filter struct fields by literals and bind them, and unpack nested structures in one go. name @ pattern checks and binds; guards (if) check relations the pattern can't express but don't count toward exhaustiveness. Binding modes: move, ref, ref mut; chosen automatically when matching on a reference. Slice patterns ([first, .., last], [x, rest @ ..]) split arrays and vectors by length.
Slice patterns
Slice patterns combine branching by length and access to the ends in one construct:
fn tanimla(v: &[i32]) -> String {
match v {
[] => String::from("boş"),
[x] => format!("tek: {x}"),
[ilk, .., son] if ilk == son => format!("uçlar eşit: {ilk}"),
[ilk, orta @ .., son] => format!("{ilk}..{son} ({} ara)", orta.len()),
}
}
The set of patterns is exhaustive: empty, single and two-or-more cover every length (even though the guarded arm doesn't count, the last arm takes the rest).
Exercise Describe a slice
Write the tanimla function above. Print the results for [], [7], [1, 2, 1] and [1, 2, 3, 4] on separate lines.
Show example solution
fn tanimla(v: &[i32]) -> String {
match v {
[] => String::from("boş"),
[x] => format!("tek: {x}"),
[ilk, .., son] if ilk == son => format!("uçlar eşit: {ilk}"),
[ilk, orta @ .., son] => format!("{ilk}..{son} ({} ara)", orta.len()),
}
}
fn main() {
let girdiler: [&[i32]; 4] = [&[], &[7], &[1, 2, 1], &[1, 2, 3, 4]];
for v in girdiler {
println!("{}", tanimla(v));
}
}
Test yourself
-
Does the pattern <code>[ilk, .., son]</code> match a single-element slice?
- Panic
- It doesn't compile
- No; at least two elements are needed
- Yes, first and last are the same
Show answer
No; at least two elements are needed — Two named positions need two separate elements; a single element needs an [x] arm.
-
Bind the middle
[ilk, orta ____ .., son] => format!("{} ara", orta.len()),
Show answer
[ilk, orta @ .., son] => format!("{} ara", orta.len()),
-
Slice and result
- []
- boş
- [7]
- tek: 7
- [1, 2, 1]
- uçlar eşit: 1
- [1, 2, 3, 4]
- 1..4 (2 ara)
Next lesson: Async web server
