constify things and remember how booleans work

src/lib.rs

@@ -65,7 +65,7 @@ impl Stringish {
 
     /// Creates a new empty `Stringish`.
     #[must_use]
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self {
             ptr: NonNull::dangling(),
             len: 0,
@@ -77,7 +77,7 @@ impl Stringish {
     ///
     /// Alternatively, use the [`Ish::ish`] method.
     #[must_use]
-    pub fn new_borrowed(s: &'static str) -> Self {
+    pub const fn new_borrowed(s: &'static str) -> Self {
         Self {
             // SAFETY: `s.as_ptr()` is never null
             ptr: unsafe { NonNull::new_unchecked(s.as_ptr() as *mut u8) },
@@ -123,13 +123,11 @@ impl Stringish {
     /// If the `Stringish` is empty, returns [`None`]. Otherwise, returns `true` if the `Stringish`
     /// is borrowed and `false` otherwise.
     #[must_use]
-    pub fn is_borrowed(&self) -> Option<bool> {
+    pub const fn is_borrowed(&self) -> Option<bool> {
         if self.len == 0 {
             None
-        } else if self.cap == 0 {
-            Some(true)
         } else {
-            Some(false)
+            Some(self.cap == 0)
         }
     }
 
@@ -138,8 +136,12 @@ impl Stringish {
     /// If the `Stringish` is empty, returns [`None`]. Otherwise, returns `true` if the `Stringish`
     /// is owned and `false` otherwise.
     #[must_use]
-    pub fn is_owned(&self) -> Option<bool> {
-        self.is_borrowed().map(|v| !v)
+    pub const fn is_owned(&self) -> Option<bool> {
+        if self.len == 0 {
+            None
+        } else {
+            Some(self.cap != 0)
+        }
     }
 
     /// Converts a borrowed `Stringish` into an owned `Stringish`, in-place.
@@ -173,7 +175,7 @@ impl Stringish {
 
     /// Returns a byte slice of this `Stringish`'s contents.
     #[must_use]
-    pub fn as_bytes(&self) -> &[u8] {
+    pub const fn as_bytes(&self) -> &[u8] {
         // SAFETY: `self.ptr` always points to `self.len` valid bytes
         unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len) }
     }
@@ -195,7 +197,7 @@ impl Stringish {
 
     /// Returns a string slice of this `Stringish`'s contents.
     #[must_use]
-    pub fn as_str(&self) -> &str {
+    pub const fn as_str(&self) -> &str {
         // SAFETY: `self.ptr` always points to valid UTF-8
         unsafe { str::from_utf8_unchecked(self.as_bytes()) }
     }