Appendix A: Keywords

The following keywords are reserved by the Rust language and may not be used as identifiers such as names of functions, variables, parameters, struct fields, modules, crates, constants, macros, static values, attributes, types, traits, or lifetimes.

Keywords Currently in Use
  • as - primitive casting, disambiguating the specific trait containing an item, or renaming items in use and extern crate statements
  • break - exit a loop immediately
  • const - constant items and constant raw pointers
  • continue - continue to the next loop iteration
  • crate - external crate linkage or a macro variable representing the crate in which the macro is defined
  • else - fallback for if and if let control flow constructs
  • enum - defining an enumeration
  • extern - external crate, function, and variable linkage
  • false - Boolean false literal
  • fn - function definition and function pointer type
  • for - iterator loop, part of trait impl syntax, and higher-ranked lifetime syntax
  • if - conditional branching
  • impl - inherent and trait implementation block
  • in - part of for loop syntax
  • let - variable binding
  • loop - unconditional, infinite loop
  • match - pattern matching
  • mod - module declaration
  • move - makes a closure take ownership of all its captures
  • mut - denotes mutability in references, raw pointers, and pattern bindings
  • pub - denotes public visibility in struct fields, impl blocks, and modules
  • ref - by-reference binding
  • return - return from function
  • Self - type alias for the type implementing a trait
  • self - method subject or current module
  • static - global variable or lifetime lasting the entire program execution
  • struct - structure definition
  • super - parent module of the current module
  • trait - trait definition
  • true - Boolean true literal
  • type - type alias and associated type definition
  • unsafe - denotes unsafe code, functions, traits, and implementations
  • use - import symbols into scope
  • where - type constraint clauses
  • while - conditional loop

Keywords Reserved for Future Use

These keywords do not have any functionality, but are reserved by Rust for potential future use.

  • abstract
  • alignof
  • become
  • box
  • do
  • final
  • macro
  • offsetof
  • override
  • priv
  • proc
  • pure
  • sizeof
  • typeof
  • unsized
  • virtual
  • yield