impl From<char> for FixedString

src/inline.rs

@@ -63,22 +63,35 @@ impl<StrRepr: Copy + AsRef<[u8]> + AsMut<[u8]> + Default + TypeSize> InlineStrin
         StrRepr::default().as_ref().len()
     }
 
-    pub fn from_str(val: &str) -> Option<Self> {
+    #[inline]
+    fn from_len_and_write(len: usize, write: impl FnOnce(&mut [u8])) -> Option<Self> {
         let mut arr = StrRepr::default();
-        if val.len() > size_of::<Self>() {
+        if len > size_of::<Self>() {
             return None;
         }
 
-        arr.as_mut()[..val.len()].copy_from_slice(val.as_bytes());
+        write(arr.as_mut());
 
-        if val.len() != Self::max_len() {
+        if len != Self::max_len() {
             // 0xFF terminate the string, to gain an extra inline character
-            arr.as_mut()[val.len()] = Self::TERMINATOR;
+            arr.as_mut()[len] = Self::TERMINATOR;
         }
 
         Some(Self { arr })
     }
 
+    pub fn from_str(val: &str) -> Option<Self> {
+        Self::from_len_and_write(val.len(), |arr| {
+            arr[..val.len()].copy_from_slice(val.as_bytes());
+        })
+    }
+
+    pub fn from_char(val: char) -> Option<Self> {
+        Self::from_len_and_write(val.len_utf8(), |arr| {
+            val.encode_utf8(arr);
+        })
+    }
+
     pub fn len(&self) -> u8 {
         // Copy to a temporary, 16 byte array to allow for SIMD impl.
         let mut buf = [0_u8; 16];

src/string.rs

@@ -294,6 +294,26 @@ impl<LenT: ValidLength> TryFrom<String> for FixedString<LenT> {
     }
 }
 
+impl<LenT: ValidLength> From<char> for FixedString<LenT> {
+    fn from(value: char) -> Self {
+        use alloc::vec;
+
+        if let Some(value) = InlineString::from_char(value) {
+            return Self(FixedStringRepr::Inline(value));
+        }
+
+        let mut bytes = vec![0; value.len_utf8()].into_boxed_slice();
+
+        value.encode_utf8(&mut bytes);
+
+        let bytes = bytes
+            .try_into()
+            .expect("len_utf8 is at most 4, so it will fit in u8");
+
+        Self(FixedStringRepr::Heap(bytes))
+    }
+}
+
 impl<LenT: ValidLength> From<FixedString<LenT>> for String {
     fn from(value: FixedString<LenT>) -> Self {
         match value.0 {
@@ -474,4 +494,63 @@ mod test {
         assert_eq!(core::mem::size_of::<FixedStringRepr<u32>>(), 13);
         assert_eq!(core::mem::align_of::<FixedStringRepr<u32>>(), 1);
     }
+
+    #[test]
+    fn from_char_u8() {
+        let s: FixedString<u8> = 'a'.into();
+        assert_eq!(s.len(), 1);
+        assert!(s.is_inline());
+
+        let s: FixedString<u8> = '¼'.into();
+        assert_eq!(s.len(), 2);
+        assert!(s.is_inline());
+
+        let s: FixedString<u8> = '⚡'.into();
+        assert_eq!(s.len(), 3);
+        assert!(s.is_inline());
+
+        let s: FixedString<u8> = '🦀'.into();
+        assert_eq!(s.len(), 4);
+        #[cfg(any(target_pointer_width = "64", target_pointer_width = "32"))]
+        assert!(s.is_inline());
+    }
+
+    #[test]
+    fn from_char_u16() {
+        let s: FixedString<u16> = 'a'.into();
+        assert_eq!(s.len(), 1);
+        assert!(s.is_inline());
+
+        let s: FixedString<u16> = '¼'.into();
+        assert_eq!(s.len(), 2);
+        assert!(s.is_inline());
+
+        let s: FixedString<u16> = '⚡'.into();
+        assert_eq!(s.len(), 3);
+        assert!(s.is_inline());
+
+        let s: FixedString<u16> = '🦀'.into();
+        assert_eq!(s.len(), 4);
+        assert!(s.is_inline());
+    }
+
+    #[test]
+    #[cfg(any(target_pointer_width = "64", target_pointer_width = "32"))]
+    fn from_char_u32() {
+        let s: FixedString<u32> = 'a'.into();
+        assert_eq!(s.len(), 1);
+        assert!(s.is_inline());
+
+        let s: FixedString<u32> = '¼'.into();
+        assert_eq!(s.len(), 2);
+        assert!(s.is_inline());
+
+        let s: FixedString<u32> = '⚡'.into();
+        assert_eq!(s.len(), 3);
+        assert!(s.is_inline());
+
+        let s: FixedString<u32> = '🦀'.into();
+        assert_eq!(s.len(), 4);
+        assert!(s.is_inline());
+    }
 }