various improvements to the 1.46 blog post

Author: steveklabnik

posts/2020-08-27-Rust-1.46.0.md

@@ -25,23 +25,54 @@ appropriate page on our website, and check out the [detailed release notes for
 
 ## What's in 1.46.0 stable
 
-This release is on the smaller side, with a number of improvements to `const
-fn`, two new standard library APIs, and one feature useful for library
-authors. See the [detailed release notes][notes] to learn about other changes
-not covered by this post.
+This release enables quite a lot of new things to appear in `const fn`, two
+new standard library APIs, and one feature useful for library authors. See
+the [detailed release notes][notes] to learn about other changes not covered
+by this post.
+
+### `const fn` improvements
+
+There are [several core language features] you can now use in a `const fn`:
+
+* `if`, `if let`, and `match`
+* `while`, `while let`, and `loop`
+* the `&&` and `||` operators
+
+You can also [cast to a slice][cast-to-slice]:
+
+```rust
+const fn foo() {
+  let x = [1, 2, 3, 4, 5];
+
+  // cast the array to a slice
+  let y: &[_] = &x;
+}
+```
+
+While these features may not feel *new*, given that you could use them all
+outside of `const fn`, they add a lot of compile-time computation power! As
+an example, the [`const-sha1` crate][sha1] can let you compute SHA-1 hashes
+at compile time. This led to a [40x performance improvement][const-perf] in
+Microsoft's WinRT bindings for Rust.
+
+[several core language features]: https://github.com/rust-lang/rust/pull/72437/
+[cast-to-slice]: https://github.com/rust-lang/rust/pull/73862/
+[sha1]: https://github.com/rylev/const-sha1
+[const-perf]: https://github.com/microsoft/winrt-rs/pull/279#issuecomment-668436700
+
 
 ### `#[track_caller]`
 
-Back in March, the release of Rust 1.42 introduced [better error messages when `unwrap()` and related functions would panic][better-errors]. At the time, we mentioned that the way
+Back in March, the release of Rust 1.42 introduced [better error messages when `unwrap` and related functions would panic][better-errors]. At the time, we mentioned that the way
 this was implemented was not yet stable. Rust 1.46 stabilizes this feature.
 
 [better-errors]: https://blog.rust-lang.org/2020/03/12/Rust-1.42.html#useful-line-numbers-in-option-and-result-panic-messages
 
-This attribute is called `#[track_caller]`, which was originally proposed
-in [RFC 2091][rfc-2091] way back in July of 2017! If you're writing a function
-like `unwrap()` that may panic but should not itself appear in the panic stacktrace, you can put this
-annotation on your functions, and the default panic formatter will use it to
-print its error message. For example, here is `unwrap` previously:
+This attribute is called `#[track_caller]`, which was originally proposed in
+[RFC 2091][rfc-2091] way back in July of 2017! If you're writing a function
+like `unwrap` that may panic, you can put this annotation on your functions,
+and the default panic formatter will use its caller as the location in its
+error message. For example, here is `unwrap` previously:
 
 ```rust
 pub fn unwrap(self) -> T {
@@ -72,28 +103,6 @@ on `std::panic::Location` to get access to this information.
 [rfc-2091]: https://github.com/rust-lang/rfcs/pull/2091
 [caller]: https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.caller
 
-### `const fn` improvements
-
-There are [several core language features] you can now use in a `const fn`:
-
-* `if`, `if let`, and `match`
-* `while`, `while let`, and `loop`
-* the `&&` and `||` operators
-
-You can also [cast to a slice][cast-to-slice]:
-
-```rust
-const fn foo() {
-  let x = [1, 2, 3, 4, 5];
-
-  // cast the array to a slice
-  let y: &[_] = &x;
-}
-```
-
-[several core language features]: https://github.com/rust-lang/rust/pull/72437/
-[cast-to-slice]: https://github.com/rust-lang/rust/pull/73862/
-
 ### Library changes
 
 Keeping with the theme of `const fn` improvements, [`std::mem::forget` is now