Rust 1.7.0 Syntax base identifier (ident) and delimiter constraints

First, identifiers

Identifier is an identifier, abbreviated in the rust syntax ident .
Ident is made up of any non-empty Unicode characters.

Example:

In the attribute syntax, there are

meta_item : ident [ ‘=‘ literal  | ‘(‘ meta_seq ‘)‘ ] ? ;

The actual use is as follows:

#![crate_type = "lib"]#![allow(dead_code)]#![feature(intrinsics, lang_items)]#[test]

The above Crate_type, allow, feature, and test are all ident.

See Rust 1.7.0 Grammar Basics attribute

Second, delimiter constraints

The rust syntax specifies which characters cannot be used as delimiters, rather than what characters can be used as delimiters.

The constraint rules are as follows:

non_nullRepresents any single Unicode character, but excludes u+0000 (that is, excludes null)
non_eolIndicates a restricted non_null , excluding carriage return u+000a (' \ n ')
non_single_quoteRepresents a restricted non_null exclusion single quote u+0027 (')
non_double_quoteRepresents non_null a restricted exclusion of double quotes u+0022 (")

Rust 1.7.0 Syntax base identifier (ident) and delimiter constraints