&str and &[u8] have the same layout

Author: sanbox-irl

src/dynamically-sized-types.md

@@ -5,7 +5,7 @@ r[dynamic-sized.intro]
 Most types have a fixed size that is known at compile time and implement the
 trait [`Sized`][sized]. A type with a size that is known only at run-time is
 called a _dynamically sized type_ (_DST_) or, informally, an unsized type.
-[Slices] and [trait objects] are two examples of <abbr title="dynamically sized
+[Slices], [trait objects], and [str] are three examples of <abbr title="dynamically sized
 types">DSTs</abbr>.
 
 r[dynamic-sized.restriction]
@@ -14,7 +14,7 @@ Such types can only be used in certain cases:
 r[dynamic-sized.pointer-types]
 * [Pointer types] to <abbr title="dynamically sized types">DSTs</abbr> are
   sized but have twice the size of pointers to sized types
-    * Pointers to slices also store the number of elements of the slice.
+    * Pointers to slices and `str` also store the number of elements of the slice.
     * Pointers to trait objects also store a pointer to a vtable.
 
 r[dynamic-sized.question-sized]
@@ -38,6 +38,7 @@ r[dynamic-sized.struct-field]
 
 [sized]: special-types-and-traits.md#sized
 [Slices]: types/slice.md
+[str]: types/textual.md
 [trait objects]: types/trait-object.md
 [Pointer types]: types/pointer.md
 [Variables]: variables.md

src/type-layout.md

@@ -89,7 +89,7 @@ Pointers to unsized types are sized. The size and alignment is guaranteed to be
 at least equal to the size and alignment of a pointer.
 
 > [!NOTE]
-> Though you should not rely on this, all pointers to <abbr title="Dynamically Sized Types">DSTs</abbr> are currently twice the size of the size of `usize` and have the same alignment.
+> Though you should not rely on this, all pointers to <abbr title="Dynamically Sized Types">DSTs</abbr> have the same alignment as usize.
 
 r[layout.array]
 ## Array Layout
@@ -110,6 +110,7 @@ r[layout.str]
 ## `str` Layout
 
 String slices are a UTF-8 representation of characters that have the same layout as slices of type `[u8]`.
+A reference `&str` has the same layout as a reference `&[u8]`.
 
 r[layout.tuple]
 ## Tuple Layout

src/types/textual.md

@@ -23,7 +23,8 @@ is valid UTF-8. Calling a `str` method with a non-UTF-8 buffer can cause
 
 r[type.text.str-unsized]
 Since `str` is a [dynamically sized type], it can only be instantiated through a
-pointer type, such as `&str`.
+pointer type, such as `&str`. The layout of `&str` is the same as the layout of
+`&[u8]`.
 
 r[type.text.layout]
 ## Layout and bit validity