Stop making me memorize the borrow checker

Shouldn't this be possible already? Deref is implemented for Arc<T>.

[1] https://doc.rust-lang.org/std/sync/struct.Arc.html#impl-Dere...

[2] https://rust-lang.github.io/rfcs/2005-match-ergonomics.html

I mean having the following work:

  match Arc::new("hello") {
      "hi" => {}
      "hello" => {}
      _ => {}
  }

It is an extension of match ergonomics, called deref patterns. There's some experimental code to make it work for `String` to `&str` (`if let "hi" = String::from("hi") {}`), but it is not anywhere close to finished. The final version will likely have something like a `trait DerefPure: Deref {}` signaling trait. There is disagreement on whether giving users the possibility to execute non-idempotent, non-cheap behavior on `Deref` and allow them to `impl DerefPure` for those types would be a big enough foot-gun to restrict this only to std or not.

What's the difference and advantage, other than less typing, of this over:

     match *Arc::new("hello").as_ref() {
      "hi" => {}
      "hello" => {}
      _ => {}

(Sorry, Rust newbie here)

Patterns can be arbitrarily complex. If you have

  struct Foo {
      bar: Arc<String>,
  }

Then it's the difference between today's

  if let Foo { bar } = val {
      if &*bar == "hi" {
      }
  }

And the potential future

  if let Foo { bar: "hi" } = val {}

The more complex the pattern, the bigger the conciseness win and levels of nesting you can remove. This comes up more often for me with `Box`, in the context of AST nodes, but because I use nightly I can use `box` patterns, which is the same feature but only for `Box` and that will never be stabilized.