diff options
| -rw-r--r-- | library/core/src/primitive_docs.rs | 28 |
1 files changed, 17 insertions, 11 deletions
diff --git a/library/core/src/primitive_docs.rs b/library/core/src/primitive_docs.rs index 6b42380d37c..87e49210874 100644 --- a/library/core/src/primitive_docs.rs +++ b/library/core/src/primitive_docs.rs @@ -291,7 +291,7 @@ mod prim_never {} /// Surrogate code points, used by UTF-16, are in the range 0xD800 to 0xDFFF. /// /// No `char` may be constructed, whether as a literal or at runtime, that is not a -/// Unicode scalar value: +/// Unicode scalar value. Violating this rule causes undefined behavior. /// /// ```compile_fail /// // Each of these is a compiler error @@ -308,9 +308,10 @@ mod prim_never {} /// let _ = unsafe { char::from_u32_unchecked(0x110000) }; /// ``` /// -/// USVs are also the exact set of values that may be encoded in UTF-8. Because -/// `char` values are USVs and `str` values are valid UTF-8, it is safe to store -/// any `char` in a `str` or read any character from a `str` as a `char`. +/// Unicode scalar values are also the exact set of values that may be encoded in UTF-8. Because +/// `char` values are Unicode scalar values and functions may assume [incoming `str` values are +/// valid UTF-8](primitive.str.html#invariant), it is safe to store any `char` in a `str` or read +/// any character from a `str` as a `char`. /// /// The gap in valid `char` values is understood by the compiler, so in the /// below example the two ranges are understood to cover the whole range of @@ -324,11 +325,10 @@ mod prim_never {} /// }; /// ``` /// -/// All USVs are valid `char` values, but not all of them represent a real -/// character. Many USVs are not currently assigned to a character, but may be -/// in the future ("reserved"); some will never be a character -/// ("noncharacters"); and some may be given different meanings by different -/// users ("private use"). +/// All Unicode scalar values are valid `char` values, but not all of them represent a real +/// character. Many Unicode scalar values are not currently assigned to a character, but may be in +/// the future ("reserved"); some will never be a character ("noncharacters"); and some may be given +/// different meanings by different users ("private use"). /// /// `char` is guaranteed to have the same size and alignment as `u32` on all /// platforms. @@ -894,8 +894,6 @@ mod prim_slice {} /// type. It is usually seen in its borrowed form, `&str`. It is also the type /// of string literals, `&'static str`. /// -/// String slices are always valid UTF-8. -/// /// # Basic Usage /// /// String literals are string slices: @@ -949,6 +947,14 @@ mod prim_slice {} /// Note: This example shows the internals of `&str`. `unsafe` should not be /// used to get a string slice under normal circumstances. Use `as_str` /// instead. +/// +/// # Invariant +/// +/// Rust libraries may assume that string slices are always valid UTF-8. +/// +/// Constructing a non-UTF-8 string slice is not immediate undefined behavior, but any function +/// called on a string slice may assume that it is valid UTF-8, which means that a non-UTF-8 string +/// slice can lead to undefined behavior down the road. #[stable(feature = "rust1", since = "1.0.0")] mod prim_str {} |