Add char::is_cased

Author: Jules-Bertholet

library/alloc/src/lib.rs

@@ -159,6 +159,7 @@
 #![feature(std_internals)]
 #![feature(str_internals)]
 #![feature(strict_provenance)]
+#![feature(titlecase)]
 #![feature(trusted_fused)]
 #![feature(trusted_len)]
 #![feature(trusted_random_access)]

library/alloc/src/str.rs

@@ -410,9 +410,9 @@ impl str {
         }
 
         fn case_ignorable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
-            use core::unicode::{Case_Ignorable, Cased};
+            use core::unicode::Case_Ignorable;
             match iter.skip_while(|&c| Case_Ignorable(c)).next() {
-                Some(c) => Cased(c),
+                Some(c) => c.is_cased(),
                 None => false,
             }
         }

library/core/src/char/methods.rs

@@ -748,6 +748,37 @@ impl char {
         }
     }
 
+    /// Returns `true` if this `char` has the `Cased` property.
+    /// A character is cased if and only if it is uppercase, lowercase, or titlecase.
+    ///
+    /// `Cased` is described in Chapter 3 (Conformance) of the [Unicode Standard] and
+    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
+    ///
+    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(titlecase)]
+    /// assert!('A'.is_cased());
+    /// assert!('a'.is_cased());
+    /// assert!(!'京'.is_cased());
+    /// ```
+    #[must_use]
+    #[unstable(feature = "titlecase", issue = "none")]
+    #[inline]
+    pub fn is_cased(self) -> bool {
+        match self {
+            'A'..='Z' | 'a'..='z' => true,
+            '\0'..='\u{A9}' => false,
+            _ => unicode::Cased(self),
+        }
+    }
+
     /// Returns `true` if this `char` has the `Lowercase` property.
     ///
     /// `Lowercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and

library/core/src/unicode/mod.rs

@@ -18,11 +18,10 @@ mod unicode_data;
 pub const UNICODE_VERSION: (u8, u8, u8) = unicode_data::UNICODE_VERSION;
 
 // For use in alloc, not re-exported in std.
-pub use unicode_data::{
-    case_ignorable::lookup as Case_Ignorable, cased::lookup as Cased, conversions,
-};
+pub use unicode_data::{case_ignorable::lookup as Case_Ignorable, conversions};
 
 pub(crate) use unicode_data::alphabetic::lookup as Alphabetic;
+pub(crate) use unicode_data::cased::lookup as Cased;
 pub(crate) use unicode_data::cc::lookup as Cc;
 pub(crate) use unicode_data::grapheme_extend::lookup as Grapheme_Extend;
 pub(crate) use unicode_data::lowercase::lookup as Lowercase;

library/core/tests/char.rs

@@ -41,6 +41,17 @@ fn test_from_str() {
     assert!(char::from_str("abc").is_err());
 }
 
+#[test]
+fn test_is_cased() {
+    assert!('a'.is_cased());
+    assert!('ö'.is_cased());
+    assert!('ß'.is_cased());
+    assert!('Ü'.is_cased());
+    assert!('P'.is_cased());
+    assert!('ª'.is_cased());
+    assert!(!'攂'.is_cased());
+}
+
 #[test]
 fn test_is_lowercase() {
     assert!('a'.is_lowercase());

library/core/tests/lib.rs

@@ -68,6 +68,7 @@
 #![feature(str_internals)]
 #![feature(std_internals)]
 #![feature(test)]
+#![feature(titlecase)]
 #![feature(trusted_len)]
 #![feature(try_blocks)]
 #![feature(try_trait_v2)]