Trim down and remove anything superflous

src/expressions/operator-expr.md

@@ -478,48 +478,17 @@ unsafe {
 assert_eq!(values[1], 3);
 ```
 
-#### Sized to sized pointer casts
+#### Pointer-to-pointer cast
 
-A sized pointer to pointer cast `*const T as *const U` or `*mut T as *mut U`
-where `T: Sized` and `U: Sized` produces a value identical to the original
-pointer.
+`*const T` / `*mut T` can be cast to `*const U` / `*mut U` under the following
+conditions:
 
-#### Unsized to unsized pointer casts
-
-Any unsized to unsized pointer cast `*const T as *const U` or `*mut T as *mut U`
-produces a value identical to the original pointer if `T` and `U` are compatible
-unsized types.
-
-For slice types like `[T]` and `[U]`, the raw pointer types `*const [T]`, `*mut
-[T]`, `*const [U]`, and `*mut [U]` encode the number of elements in this slice.
-Casts between these raw pointer types preserve the number of elements. Note
-that, as a consequence, such casts do *not* necessarily preserve the size of the
-pointer's referent (e.g., casting `*const [u16]` to `*const [u8]` will result in
-a raw pointer which refers to an object of half the size of the original). The
-same holds for `str` and any compound type whose unsized tail is a slice type,
-such as struct `Foo(i32, [u8])` or `(u64, Foo)`.
-
-#### Unsized to sized pointer casts
-
-Any wide to narrow pointer cast discards all metadata that completes the wide
-pointer and produces a thin base pointer.
-
-The following casts are well-defined:
-
-* `*const [T] to *const U` or `*mut [T] to *mut U` discards the length of the
-  slice and produces a pointer to the first element. The produced pointer is
-  casted to `U` in the same manner as a sized pointer to pointer cast.
-* `*const dyn T to *const U` or `*mut dyn T to *mut U` discards all metadata
-  associated with the [trait object] and produces a pointer to the instance from
-  which the trait object was constructed. The produced pointer is casted to `U`
-  in the same manner as a sized pointer to pointer cast.
-
-For example:
-
-* `*const [u32] as *const u8` would produce a pointer to the first element
-  constituting the slice, casted to a `*const u8` pointer.
-* `*const str` and `*mut str` have the same semantics as `*const [u8]` and `*mut
-  [u8]` since they have [identical layouts][_str_layout_].
+- If both `T` and `U` are sized, the cast produces a value identical to the
+  original pointer.
+- If both `T` and `U` are unsized, the cast produces a value identical to the
+  original pointer if `T` and `U` are compatible unsized types.
+- If `T` is unsized and `U` is sized, the cast discards all metadata that
+  completes the wide pointer `T` and produces a thin base pointer `U`.
 
 ## Assignment expressions
 
@@ -704,8 +673,6 @@ See [this test] for an example of using this dependency.
 [undefined behavior]: ../behavior-considered-undefined.md
 [addr_of]: ../../std/ptr/macro.addr_of.html
 [addr_of_mut]: ../../std/ptr/macro.addr_of_mut.html
-[slice]: ../types/slice.md
-[trait object]: ../types/trait-object.md
 
 [_BorrowExpression_]: #borrow-operators
 [_DereferenceExpression_]: #the-dereference-operator
@@ -722,4 +689,3 @@ See [this test] for an example of using this dependency.
 [_TypeNoBounds_]: ../types.md#type-expressions
 [_RangeExpression_]: ./range-expr.md
 [_UnderscoreExpression_]: ./underscore-expr.md
-[_str_layout_]: ../type-layout.md#str-layout