Rust Pig Latin exercise solution

Question

I just finished the chapter about collections from the Rust book, and it recommended trying some exercises provided there, such as a Pig Latin translator.

Convert strings to pig latin. The first consonant of each word is moved to the end of the word and “ay” is added, so “first” becomes “irst-fay.” Words that start with a vowel have “hay” added to the end instead (“apple” becomes “apple-hay”). Keep in mind the details about UTF-8 encoding!

use std::io;
fn main() {
    let mut inp = String::new();
    io::stdin().read_line(&mut inp).expect("Could not read");
    inp.remove(inp.len() - 1); // newline
    let cha = inp.chars().next().expect("Empty string");
    if is_consonant(cha) {
        inp += "-hay";
    } else {
        inp.remove(0);
        inp += &format!("-{}ay", cha);
    }
    println!("{}", inp);
}

fn is_consonant(c: char) -> bool {
    ['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'].contains(&c)
}

Does my code satisfy whatever is required for it to be idiomatic Rust?

Answer 1

Suggested improvements:

Use trim() to remove the newline and other white spaces.

let mut inp = inp.trim().to_string();

---

The function is_consonant() actually checks if a letter is a vowel so it should be renamed.

---

The vowels can be extracted into a const.

const VOWELS: [char; 10] = ['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'];

---

The is_vowel(c: char) function can take reference to a char since that it what it uses.

fn is_vowel(c: &char) -> bool {
    VOWELS.contains(c)
}

Final Code:

use std::io;

const VOWELS: [char; 10] = ['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'];

fn main() {
    let mut inp = String::new();
    io::stdin().read_line(&mut inp).expect("Could not read");
    let mut inp = inp.trim().to_string();

    let cha = inp.chars().next().expect("Empty string");

    if is_vowel(&cha) {
        inp += "-hay";
    } else {
        inp.remove(0);
        inp += &format!("-{}ay", cha);
    }

    println!("{}", inp);
}

fn is_vowel(c: &char) -> bool {
    VOWELS.contains(c)
}

---

Additional changes:

It is possible to avoid some String allocations but doing so makes the code a bit more unreadable (in my opinion). Nonetheless I feel like it is worth at least mentioning them.

---

Replace format! by pushing to the original string to avoid a String allocation.

inp.remove(0);
inp += &format!("-{}ay", cha);

Can be replaced with:

inp.remove(0);
inp.push('-');
inp.push(cha);
inp.push_str("ay");

---

Avoid cloning the input String after trimming the whitespaces.

let mut inp = inp.trim().to_string();

Can be replaced with:

inp.truncate(inp.trim().len());

---

Convert the first character to lower case before checking if it is a vowel.

let cha = inp.chars().next().expect("Empty string");

Can be replaced with:

let cha = inp.chars().next().expect("Empty string").to_lowercase().next().unwrap();