3 ms·
I mean having the following work: match Arc::new("hello") { "hi" => {} "hello" => {} _ => {} } It is an extension of match ergonomics, c
by estebank 2y ago
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.
- sfink 2y agoWhat's the difference and advantage, other than less typing, of this over: match *Arc::new("hello").as_ref() { "hi" => {} "hello" => {} _ => {} (Sorry, Rust newbie here)
- estebank 2y agoPatterns 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.