From cec158b6b7c488c93f16bbe07b6082d5e4f2f7b1 Mon Sep 17 00:00:00 2001 From: "NODA, Kai" Date: Thu, 11 Feb 2016 00:55:47 +0800 Subject: [PATCH] doc: concat_idents! macro: more on its limitations. Signed-off-by: NODA, Kai --- src/libstd/macros.rs | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs index b7afd12d8e527..d241cd032ed4c 100644 --- a/src/libstd/macros.rs +++ b/src/libstd/macros.rs @@ -269,9 +269,10 @@ pub mod builtin { /// This macro takes any number of comma-separated identifiers, and /// concatenates them all into one, yielding an expression which is a new /// identifier. Note that hygiene makes it such that this macro cannot - /// capture local variables, and macros are only allowed in item, - /// statement or expression position, meaning this macro may be difficult to - /// use in some situations. + /// capture local variables. Also, as a general rule, macros are only + /// allowed in item, statement or expression position. That means while + /// you may use this macro for referring to existing variables, functions or + /// modules etc, you cannot define a new one with it. /// /// # Examples /// @@ -283,6 +284,8 @@ pub mod builtin { /// /// let f = concat_idents!(foo, bar); /// println!("{}", f()); + /// + /// // fn concat_idents!(new, fun, name) { } // not usable in this way! /// # } /// ``` #[stable(feature = "rust1", since = "1.0.0")]