feat: add to_folded_case() method

src/lib.rs

@@ -138,6 +138,24 @@ impl<S: AsRef<str>> UniCase<S> {
             UniCase(Encoding::Unicode(Unicode(s)))
         }
     }
+
+    /// Returns a copy of this string where each character is mapped to its
+    /// Unicode CaseFolding equivalent.
+    ///
+    /// # Note
+    ///
+    /// Unicode Case Folding is meant for string storage and matching, not for
+    /// display.
+    pub fn to_folded_case(&self) -> String {
+        #[cfg(not(__unicase__core_and_alloc))]
+        #[allow(deprecated, unused)]
+        use std::ascii::AsciiExt;
+
+        match self.0 {
+            Encoding::Ascii(ref s) => s.0.as_ref().to_ascii_lowercase(),
+            Encoding::Unicode(ref s) => s.to_folded_case(),
+        }
+    }
 }
 
 impl<S> UniCase<S> {

src/unicode/mod.rs

@@ -1,3 +1,5 @@
+#[cfg(all(__unicase__core_and_alloc, not(test)))]
+use alloc::string::String;
 #[cfg(__unicase__iter_cmp)]
 use core::cmp::Ordering;
 use core::hash::{Hash, Hasher};
@@ -8,6 +10,12 @@ mod map;
 #[derive(Clone, Copy, Debug, Default)]
 pub struct Unicode<S>(pub S);
 
+impl<S: AsRef<str>> Unicode<S> {
+    pub fn to_folded_case(&self) -> String {
+        self.0.as_ref().chars().flat_map(lookup).collect()
+    }
+}
+
 impl<S1: AsRef<str>, S2: AsRef<str>> PartialEq<Unicode<S2>> for Unicode<S1> {
     #[inline]
     fn eq(&self, other: &Unicode<S2>) -> bool {
@@ -184,6 +192,11 @@ mod tests {
         eq!("ᾲ στο διάολο", "ὰι στο διάολο");
     }
 
+    #[test]
+    fn test_to_folded_case() {
+        assert_eq!(Unicode("Maße").to_folded_case(), "masse");
+    }
+
     #[cfg(feature = "nightly")]
     #[bench]
     fn bench_ascii_folding(b: &mut ::test::Bencher) {