Testing exercises/standard_library_types/iterators2.rs

code review
1

rustlings, I modified iterators2.rs as follows, I cannot build this test.
the build spends a lot of time with no result.
Please help me.

pub fn capitalize_first(input: &str) -> String {
let mut c = input.chars();
let mut result = String::new();
while let Some(first) = c.next() {
    let len = result.len();
    if len == 0 {
        result.push(first.to_ascii_uppercase());
    } else {
        result.push(first);
    }
}
result

}

#[cfg(test)]
mod tests {
use super::*;

// Step 1.
// Tests that verify your `capitalize_first` function implementation
#[test]
fn test_success() {
    assert_eq!(capitalize_first("hello"), "Hello");
}

#[test]
fn test_empty() {
    assert_eq!(capitalize_first(""), "");
}

// Step 2.
#[test]
fn test_iterate_string_vec() {
    let words = vec!["hello", "world"];
    let capitalized_words: Vec<_> = words.iter().map(|&word| capitalize_first(word)).collect(); // TODO
    assert_eq!(capitalized_words, ["Hello", "World"]);
}

#[test]
fn test_iterate_into_string() {
    let words = vec!["hello", " ", "world"];
    let mut capitalized_words: String = String::new();
    while let Some(&word) = words.iter().next() {
        let str = capitalize_first(word);
        capitalized_words.push_str(&str);
    }
    assert_eq!(capitalized_words, "Hello World");
}

}Preformatted text

2

In the future try to format the code completely so it shows up nicely in the forum. The easiest way is to put all the code between a pair of three backticks like so

```
Put your code here
```

As far as your question, your last test has the following line

while let Some(&word) = words.iter().next() {

This is creating a new iterator that starts from the beginning of the vector for each time through the loop, making an infinite loop. This can either be changed to

let mut iter = words.iter();
while let Some(&word) = iter.next() {

Or you can just use a for loop directly which wouldn’t have this problem to worry about

for word in words.iter() {

The for loop syntax effectively handles the reuse of the same iterator for you

3

Thanks for your help

4

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