liballoc/{String,Vec}: constify existing functions instead

Author: npry

library/alloc/src/raw_vec.rs

@@ -273,15 +273,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
     /// be careful.
     #[inline]
-    pub fn ptr(&self) -> *mut T {
-        self.ptr.as_ptr()
-    }
-
-    /// Gets a const raw pointer to the start of the allocation. Note that this is
-    /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
-    /// be careful.
-    #[inline]
-    pub const fn ptr_const(&self) -> *mut T {
+    pub const fn ptr(&self) -> *mut T {
         self.ptr.as_ptr()
     }
 
@@ -294,7 +286,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     ///
     /// This will always be `usize::MAX` if `T` is zero-sized.
     #[inline(always)]
-    pub fn capacity(&self) -> usize {
+    pub const fn capacity(&self) -> usize {
         if T::IS_ZST { usize::MAX } else { self.cap.0 }
     }
 

library/alloc/src/string.rs

@@ -1006,7 +1006,8 @@ impl String {
     #[inline]
     #[must_use = "`self` will be dropped if the result is not used"]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn into_bytes(self) -> Vec<u8> {
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
+    pub const fn into_bytes(self) -> Vec<u8> {
         self.vec
     }
 
@@ -1022,38 +1023,8 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "string_as_str", since = "1.7.0")]
-    pub fn as_str(&self) -> &str {
-        self.as_str_const()
-    }
-
-    /// Extracts a const string slice containing the entire `String`.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// # use std::borrow::Cow;
-    /// // `Deref`, `AsRef`, and `as_str` are not available in `const` contexts, so this doesn't otherwise work.
-    /// const fn cow_str<'c, 's>(c: &Cow<'s, str>) -> &'c str
-    /// where 's: 'c {
-    ///     match c {
-    ///         Cow::Borrowed(s) => s,
-    ///         Cow::Owned(s) => s.as_str_const(),
-    ///     }
-    /// }
-    ///
-    /// const STRING: Cow<'static, str> = Cow::Owned(String::new());
-    /// const STR: Cow<'static, str> = Cow::Borrowed("foo");
-    ///
-    /// const SLICED_STRING: &'static str = cow_str(&STRING);
-    /// const SLICED_STR: &'static str = cow_str(&STR);
-    ///
-    /// assert_eq!(SLICED_STRING, "");
-    /// assert_eq!(SLICED_STR, "foo");
-    /// ```
-    #[inline]
-    #[must_use]
-    #[unstable(feature = "const_vec_string_slice", issue = "none")]
-    pub const fn as_str_const(&self) -> &str {
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
+    pub const fn as_str(&self) -> &str {
         unsafe { str::from_utf8_unchecked(self.vec.as_slice_const()) }
     }
 
@@ -1143,7 +1114,8 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn capacity(&self) -> usize {
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
+    pub const fn capacity(&self) -> usize {
         self.vec.capacity()
     }
 
@@ -1406,7 +1378,8 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn as_bytes(&self) -> &[u8] {
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
+    pub const fn as_bytes(&self) -> &[u8] {
         &self.vec
     }
 
@@ -1779,8 +1752,9 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
     #[rustc_confusables("length", "size")]
-    pub fn len(&self) -> usize {
+    pub const fn len(&self) -> usize {
         self.vec.len()
     }
 
@@ -1798,7 +1772,8 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn is_empty(&self) -> bool {
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
+    pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }
 

library/alloc/src/vec/mod.rs

@@ -944,7 +944,8 @@ impl<T, A: Allocator> Vec<T, A> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn capacity(&self) -> usize {
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
+    pub const fn capacity(&self) -> usize {
         self.buf.capacity()
     }
 
@@ -1251,37 +1252,8 @@ impl<T, A: Allocator> Vec<T, A> {
     /// ```
     #[inline]
     #[stable(feature = "vec_as_slice", since = "1.7.0")]
-    pub fn as_slice(&self) -> &[T] {
-        self.as_slice_const()
-    }
-
-    /// Extracts a slice containing the entire vector.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// # use std::borrow::Cow;
-    /// // `Deref`, `AsRef`, and `as_slice` are not available in `const` contexts, so this doesn't otherwise work.
-    /// const fn cow_slice<'c, 's>(c: &Cow<'s, [u8]>) -> &'c [u8]
-    /// where 's: 'c {
-    ///     match c {
-    ///         Cow::Borrowed(s) => s,
-    ///         Cow::Owned(s) => s.as_slice_const(),
-    ///     }
-    /// }
-    ///
-    /// const VEC: Cow<'static, [u8]> = Cow::Owned(Vec::new());
-    /// const SLICE: Cow<'static, [u8]> = Cow::Borrowed(b"foo");
-    ///
-    /// const SLICED_VEC: &'static [u8] = cow_slice(&VEC);
-    /// const SLICED_SLICE: &'static [u8] = cow_slice(&SLICE);
-    ///
-    /// assert_eq!(SLICED_VEC, b"");
-    /// assert_eq!(SLICED_SLICE, b"foo");
-    /// ```
-    #[inline]
-    #[unstable(feature = "const_vec_string_slice", issue = "none")]
-    pub const fn as_slice_const(&self) -> &[T] {
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
+    pub const fn as_slice(&self) -> &[T] {
         unsafe { slice::from_raw_parts(self.as_ptr_const(), self.len) }
     }
 
@@ -1354,76 +1326,15 @@ impl<T, A: Allocator> Vec<T, A> {
     /// [`as_mut_ptr`]: Vec::as_mut_ptr
     /// [`as_ptr`]: Vec::as_ptr
     #[stable(feature = "vec_as_ptr", since = "1.37.0")]
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
     #[rustc_never_returns_null_ptr]
     #[inline]
-    pub fn as_ptr(&self) -> *const T {
+    pub const fn as_ptr(&self) -> *const T {
         // We shadow the slice method of the same name to avoid going through
         // `deref`, which creates an intermediate reference.
         self.buf.ptr()
     }
 
-    /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
-    /// valid for zero sized reads if the vector didn't allocate.
-    ///
-    /// This is a `const` version of [`as_ptr`].
-    ///
-    /// The caller must ensure that the vector outlives the pointer this
-    /// function returns, or else it will end up pointing to garbage.
-    /// Modifying the vector may cause its buffer to be reallocated,
-    /// which would also make any pointers to it invalid.
-    ///
-    /// The caller must also ensure that the memory the pointer (non-transitively) points to
-    /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
-    /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
-    ///
-    /// This method guarantees that for the purpose of the aliasing model, this method
-    /// does not materialize a reference to the underlying slice, and thus the returned pointer
-    /// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
-    /// Note that calling other methods that materialize mutable references to the slice,
-    /// or mutable references to specific elements you are planning on accessing through this pointer,
-    /// as well as writing to those elements, may still invalidate this pointer.
-    /// See the second example below for how this guarantee can be used.
-    ///
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// let x = vec![1, 2, 4];
-    /// let x_ptr = x.as_ptr_const();
-    ///
-    /// unsafe {
-    ///     for i in 0..x.len() {
-    ///         assert_eq!(*x_ptr.add(i), 1 << i);
-    ///     }
-    /// }
-    /// ```
-    ///
-    /// Due to the aliasing guarantee, the following code is legal:
-    ///
-    /// ```rust
-    /// unsafe {
-    ///     let mut v = vec![0, 1, 2];
-    ///     let ptr1 = v.as_ptr_const();
-    ///     let _ = ptr1.read();
-    ///     let ptr2 = v.as_mut_ptr().offset(2);
-    ///     ptr2.write(2);
-    ///     // Notably, the write to `ptr2` did *not* invalidate `ptr1`
-    ///     // because it mutated a different element:
-    ///     let _ = ptr1.read();
-    /// }
-    /// ```
-    ///
-    /// [`as_mut_ptr`]: Vec::as_mut_ptr
-    /// [`as_ptr_const`]: Vec::as_ptr
-    #[rustc_never_returns_null_ptr]
-    #[unstable(feature = "const_vec_string_slice", issue = "none")]
-    #[inline]
-    pub const fn as_ptr_const(&self) -> *const T {
-        // We shadow the slice method of the same name to avoid going through
-        // `deref`, which creates an intermediate reference.
-        self.buf.ptr_const()
-    }
-
     /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
     /// raw pointer valid for zero sized reads if the vector didn't allocate.
     ///
@@ -2352,8 +2263,9 @@ impl<T, A: Allocator> Vec<T, A> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
     #[rustc_confusables("length", "size")]
-    pub fn len(&self) -> usize {
+    pub const fn len(&self) -> usize {
         self.len
     }
 
@@ -2369,7 +2281,8 @@ impl<T, A: Allocator> Vec<T, A> {
     /// assert!(!v.is_empty());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn is_empty(&self) -> bool {
+    #[rustc_const_unstable(feature = "const_vec_string_slice")]
+    pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }