From 1e9aad752beb789df4f2232adf6b9a24efbdac8d Mon Sep 17 00:00:00 2001 From: est31 Date: Wed, 9 Nov 2016 07:23:57 +0100 Subject: [PATCH] Document the question mark operator --- src/doc/book/syntax-index.md | 2 ++ src/doc/reference.md | 8 ++++++-- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/src/doc/book/syntax-index.md b/src/doc/book/syntax-index.md index 1e05b01d30d46..28403711cd701 100644 --- a/src/doc/book/syntax-index.md +++ b/src/doc/book/syntax-index.md @@ -94,6 +94,7 @@ * `|=` (`var |= expr`): bitwise or & assignment. Overloadable (`BitOrAssign`). * `||` (`expr || expr`): logical or. * `_`: "ignored" pattern binding (see [Patterns (Ignoring bindings)]). Also used to make integer-literals readable (see [Reference (Integer literals)]). +* `?` (`expr?`): Error propagation. Returns early when `Err(_)` is encountered, unwraps otherwise. Similar to the [`try!` macro]. ## Other Syntax @@ -210,6 +211,7 @@ [Functions]: functions.html [Generics]: generics.html [Iterators]: iterators.html +[`try!` macro]: error-handling.html#the-try-macro [Lifetimes]: lifetimes.html [Loops (`for`)]: loops.html#for [Loops (`loop`)]: loops.html#loop diff --git a/src/doc/reference.md b/src/doc/reference.md index 4838ecd2d42e6..eb3a6c0de6d42 100644 --- a/src/doc/reference.md +++ b/src/doc/reference.md @@ -2860,8 +2860,8 @@ assert_eq!(x, y); ### Unary operator expressions -Rust defines the following unary operators. They are all written as prefix operators, -before the expression they apply to. +Rust defines the following unary operators. With the exception of `?`, they are +all written as prefix operators, before the expression they apply to. * `-` : Negation. Signed integer types and floating-point types support negation. It @@ -2890,6 +2890,10 @@ before the expression they apply to. If the `&` or `&mut` operators are applied to an rvalue, a temporary value is created; the lifetime of this temporary value is defined by [syntactic rules](#temporary-lifetimes). +* `?` + : Propagating errors if applied to `Err(_)` and unwrapping if + applied to `Ok(_)`. Only works on the `Result` type, + and written in postfix notation. ### Binary operator expressions