case_folds.rs

use std::str;

struct UpperChars<'a> {
  chars: str::Chars<'a>
}

struct LowerChars<'a> {
  chars: str::Chars<'a>
}

fn upper_chars<'a>(s: &'a str) -> UpperChars<'a> {
  UpperChars { chars: s.chars() }
}

fn lower_chars<'a>(s: &'a str) -> LowerChars<'a> {
  LowerChars { chars: s.chars() }
}

impl<'a> Iterator<char> for LowerChars<'a> {
  fn next(&mut self) -> Option<char> {
    self.chars.next().map(|c| c.to_lowercase())
  }
}

impl<'a> Iterator<char> for UpperChars<'a> {
  fn next(&mut self) -> Option<char> {
    self.chars.next().map(|c| c.to_uppercase())
  }
}
pub trait CaseFolds {
  fn to_uppercase(&self) -> String;
  fn to_lowercase(&self) -> String;
}

impl<'a> CaseFolds for &'a String {
  fn to_lowercase(&self) -> String {
    lower_chars((*self).as_slice()).collect::<String>()
  }
  fn to_uppercase(&self) -> String {
    upper_chars((*self).as_slice()).collect::<String>()
  }
}

impl<'a> CaseFolds for &'a str {
  fn to_lowercase(&self) -> String {
    lower_chars((*self).as_slice()).collect::<String>()
  }
  fn to_uppercase(&self) -> String {
    upper_chars((*self).as_slice()).collect::<String>()
  }
}

#[cfg(test)]
mod tests {
  use super::CaseFolds;
  #[test]
  fn string_to_lowercase() {
    let gl = String::from_str("στιγμασ");
    assert_eq!("ΣΤΙΓΜΑΣ".to_lowercase(), gl);
  }
}