特性`std::borrow::Borrow<char> ` 没有为 `&amp;str` 实现

Question

let mut map: HashMap<&str, u32> = HashMap::new();

for (i, c) in text.chars().enumerate() {
    if map.contains_key(&c) {
    // Do something
    }
}

the trait std::borrow::Borrow<char> is not implemented for &str

I need an explanation of this error and how to fix it please. I am looping through every character in a text and inserting the ones not already in a hashmap into the hash map. But i keep getting the error as stated above.

Answer 1

chars is an Iterator , whose Item = char , so your HashMap<&str, u32> is not compatible with it.

&str is a string slice (essentialy a sequence of characters), while a char is a single character.

You must decide:

• Should map really map from &str to u32 ? Or possibly from char ? Or possibly from &char ?
• If you go for &str , you must convert chars 's elements to &str .