Rust
Processing with iterators
Chain commands with iterators.
Processing with iterators
The search command must filter the notes together with their numbers. An enumerate and filter chain does this without building an intermediate collection:
impl Defter {
fn ara(&self, sorgu: &str) -> Vec<(usize, &String)> {
let s = sorgu.to_lowercase();
self.notlar
.iter()
.enumerate()
.filter(|(_, n)| n.to_lowercase().contains(&s))
.map(|(i, n)| (i + 1, n))
.collect()
}
}
Adding the number before filter matters; otherwise the displayed number wouldn't reflect the note's real position.
Summary statistics
Iterators are ideal for short reports too:
let toplam_karakter: usize = d.notlar.iter().map(|n| n.chars().count()).sum();
let en_uzun = d.notlar.iter().max_by_key(|n| n.chars().count());
println!("{} not, {} karakter, en uzun: {:?}",
d.notlar.len(), toplam_karakter, en_uzun);
Exercise Search notes
Add the ara method to Defter. Add the notes "süt al", "kod yaz" and "süt faturası", and print the results of ara("süt") as N. note.
Show example solution
struct Defter {
notlar: Vec<String>,
}
impl Defter {
fn new() -> Self {
Self { notlar: Vec::new() }
}
fn ekle(&mut self, metin: String) {
self.notlar.push(metin);
}
}
impl Defter {
fn ara(&self, sorgu: &str) -> Vec<(usize, &String)> {
let s = sorgu.to_lowercase();
self.notlar
.iter()
.enumerate()
.filter(|(_, n)| n.to_lowercase().contains(&s))
.map(|(i, n)| (i + 1, n))
.collect()
}
}
fn main() {
let mut d = Defter::new();
for n in ["süt al", "kod yaz", "süt faturası"] {
d.ekle(n.to_string());
}
for (i, n) in d.ara("süt") {
println!("{}. {}", i, n);
}
}
Test yourself
-
What would happen if <code>enumerate</code> were called after <code>filter</code>?
- Numbers would count 1, 2, 3 among the matches only
- Compile error
- The result wouldn't change
- Panic
Show answer
Numbers would count 1, 2, 3 among the matches only — The order of adapters changes the meaning; since the delete command needs the real number, enumerate must come first.
-
Filter the matches
.enumerate()
.____(|(_, n)| n.to_lowercase().contains(&s))
Show answer
.enumerate()
.filter(|(_, n)| n.to_lowercase().contains(&s))
-
Query and matching numbers
- "süt"
- 1, 3
- "KOD"
- 2
- "fatura"
- 3
- "çay"
- None
Next lesson: Error and exit
