(#1) add char_count api because that information comes free

src/borrowed.rs

@@ -58,6 +58,13 @@ impl<'a> IndexedChars<'a> {
         self.inner.get_char(self.buf, index)
     }
 
+    /// Returns the number of chars present in the backing string, this operation is free thanks to
+    /// how [`IndexedChars`] is constructed
+    #[must_use]
+    pub fn char_count(&self) -> usize {
+        self.inner.char_count(self.buf)
+    }
+
     /// Returns a reference to the backing `&str`
     #[must_use]
     pub fn as_str(&self) -> &str {

src/indexed_chars.rs

@@ -18,6 +18,7 @@ impl IndexedCharsInner {
     pub(crate) fn new(s: &str) -> Self {
         // this is expensive but it lets us avoid big reallocs
         // it also lets us niche on ascii strings
+        // maybe-TODO(ultrabear) replace with no-std bytecount::num_chars?
         let charlen = s.chars().count();
 
         // if the number of chars is equal to the number of bytes we can skip allocating at all
@@ -63,6 +64,16 @@ impl IndexedCharsInner {
         self.chars.is_empty()
     }
 
+    /// Computes the amount of chars in the given string in O(1) time,
+    /// the string passed must be the one this index was created with.
+    pub(crate) fn char_count(&self, buf: &str) -> usize {
+        if self.is_ascii() {
+            buf.len()
+        } else {
+            self.chars.len()
+        }
+    }
+
     /// Gets a char from a string using the index, the string passed must be the one this index was created with
     pub(crate) fn get_char(&self, buf: &str, index: usize) -> Option<char> {
         // niche on empty chars (ascii optimization)

src/owned.rs

@@ -64,6 +64,13 @@ impl OwnedIndexedChars {
         self.inner.get_char(&self.buf, index)
     }
 
+    /// Returns the number of chars present in the backing string, this operation is free thanks to
+    /// how [`OwnedIndexedChars`] is constructed
+    #[must_use]
+    pub fn char_count(&self) -> usize {
+        self.inner.char_count(&self.buf)
+    }
+
     /// Drops index data and returns backing `String` allocation.
     #[must_use]
     pub fn into_string(self) -> String {