From 7e4a1459e928791c3905ee4cb30813f222e4c8ca Mon Sep 17 00:00:00 2001 From: Steve Klabnik Date: Thu, 28 Aug 2014 15:12:18 -0400 Subject: [PATCH] note about ref patterns in pointer guide Fixes #13602 --- src/doc/guide-pointers.md | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/src/doc/guide-pointers.md b/src/doc/guide-pointers.md index b196997b399c4..6492400a2cfc7 100644 --- a/src/doc/guide-pointers.md +++ b/src/doc/guide-pointers.md @@ -729,6 +729,31 @@ This part is coming soon. This part is coming soon. +# Patterns and `ref` + +When you're trying to match something that's stored in a pointer, there may be +a situation where matching directly isn't the best option available. Let's see +how to properly handle this: + +```{rust,ignore} +fn possibly_print(x: &Option) { + match *x { + // BAD: cannot move out of a `&` + Some(s) => println!("{}", s) + + // GOOD: instead take a reference into the memory of the `Option` + Some(ref s) => println!("{}", *s), + None => {} + } +} +``` + +The `ref s` here means that `s` will be of type `&String`, rather than type +`String`. + +This is important when the type you're trying to get access to has a destructor +and you don't want to move it, you just want a reference to it. + # Cheat Sheet Here's a quick rundown of Rust's pointer types: