相关疑难解决方法(0)

在做rustlings 时standard_library_types/iterators2.rs，我开始想知道如何std::iter::Iterator::map调用它的参数闭包/函数。更具体地说，假设我有一个功能

// "hello" -> "Hello"
pub fn capitalize_first(input: &str) -> String {
    let mut c = input.chars();
    match c.next() {
        None => String::new(),
        Some(first) => String::from(first.to_ascii_uppercase()) + c.as_str(),
    }
}

现在我想用它

// Apply the `capitalize_first` function to a slice of string slices.
// Return a vector of strings.
// ["hello", "world"] -> ["Hello", "World"]
pub fn capitalize_words_vector(words: &[&str]) -> Vec<String> {
    words.into_iter().map(capitalize_first).collect()
}

哪个不编译

error[E0631]: type mismatch in function arguments
  --> exercises/standard_library_types/iterators2.rs:24:27
   |
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