Rust replace beginning of string generically

replace_str.rs

use std::borrow::Cow;

pub trait ReplaceBeginning<'a>: Into<Cow<'a, str>> {
    fn replace_beginning(
        self,
        prefix: impl AsRef<str>,
        replacement: impl AsRef<str>,
    ) -> Cow<'a, str> {
        let new_self = self.into();
        let prefix = prefix.as_ref();
        if !new_self.starts_with(prefix) {
            return new_self;
        }
        let mut result = new_self.to_string();
        result.replace_range(..prefix.len(), replacement.as_ref());
        result.into()
    }
}

impl<'a, T: Into<Cow<'a, str>>> ReplaceBeginning<'a> for T {}

pub trait ReplaceEnding<'a>: Into<Cow<'a, str>> {
    fn replace_ending(self, prefix: impl AsRef<str>, replacement: impl AsRef<str>) -> Cow<'a, str> {
        let new_self = self.into();
        let prefix = prefix.as_ref();
        if !new_self.ends_with(prefix) {
            return new_self;
        }
        let mut result = new_self.to_string();
        result.replace_range(new_self.len() - prefix.len().., replacement.as_ref());
        result.into()
    }
}

impl<'a, T: Into<Cow<'a, str>>> ReplaceEnding<'a> for T {}

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

    #[test]
    fn test_replace_beginning() {
        let s = "hello world";
        let result = s.replace_beginning("hello", "hi");
        assert_eq!(result, "hi world");
    }

    #[test]
    fn test_replace_beginning_no_change() {
        let s = "hello world";
        let result = s.replace_beginning("xyz", "hi");
        assert_eq!(result, s);
    }

    #[test]
    fn test_prepend() {
        let s = "world";
        let result = s.replace_beginning("", "hello, ");
        assert_eq!(result, "hello, world");
    }

    #[test]
    fn test_replace_ending() {
        let s = "hello world";
        let result = s.replace_ending("world", "everyone");
        assert_eq!(result, "hello everyone");
    }

    #[test]
    fn test_replace_ending_no_change() {
        let s = "hello world";
        let result = s.replace_ending("xyz", "hi");
        assert_eq!(result, s);
    }

    #[test]
    fn test_replace_ending_one_char() {
        let s = "hello world";
        let result = s.replace_ending("d", "ds");
        assert_eq!(result, "hello worlds");
    }
    #[test]
    fn test_append_ending() {
        let s = "hello world";
        let result = s.replace_ending("", "s");
        assert_eq!(result, "hello worlds");
    }
}