Rust for C-Programmers

5.2 Identifiers and Allowed Characters

Identifiers are names given to entities like variables, functions, types, modules, etc. In Rust:

1. Allowed Characters: Identifiers must start with a Unicode character belonging to the XID_Start category or an underscore (_). Subsequent characters can be from XID_Start, XID_Continue, or _.
   • XID_Start includes most letters from scripts around the world (Latin, Greek, Cyrillic, Han, etc.).
   • XID_Continue includes XID_Start characters plus digits, underscores, and various combining marks.
   • This means identifiers like привет, 数据, my_variable, _internal, and isValid are valid.
2. Restrictions:
   • Standard ASCII digits (0-9) cannot be the first character (unless using raw identifiers, e.g., r#1st_variable, which is highly discouraged).
   • Keywords cannot be used as identifiers unless escaped with r#.
   • Spaces, punctuation (like !, ?, ., -), and symbols (like #, @, $) are generally not allowed within identifiers.
3. Encoding: Identifiers must be valid UTF-8.
4. Length: No explicit length limit, but overly long identifiers harm readability.

Naming Conventions (Style, Not Enforced by Compiler):

• snake_case: Used for variable names, function names, module names (e.g., let user_count = 5;, fn calculate_mean() {}, mod network_utils {}).
• UpperCamelCase: Used for type names (structs, enums, traits) and enum variants (e.g., struct UserAccount {}, enum Status { Connected, Disconnected }, trait Serializable {}).
• SCREAMING_SNAKE_CASE: Used for constants and statics (e.g., const MAX_CONNECTIONS: u32 = 100;, static DEFAULT_PORT: u16 = 8080;).

These conventions enhance readability and are strongly recommended.