Keywords and Reserved Words

Keywords are reserved words that have special meaning in the language.

Keywords

The following words are keywords and cannot be used as identifiers:

Keyword	Description
`borrow`	Borrow parameter mode
`fn`	Function declaration
`inout`	Inout parameter mode
`let`	Variable binding
`linear`	Linear struct modifier
`mut`	Mutable binding modifier
`if`	Conditional expression
`else`	Alternative branch
`while`	While loop expression
`loop`	Infinite loop expression
`for`	For loop expression
`in`	Iterable separator in a `for` loop
`match`	Pattern matching expression
`return`	Return from function
`break`	Exit loop
`comptime`	Compile-time evaluation
`continue`	Skip to next iteration
`true`	Boolean literal
`false`	Boolean literal
`struct`	Struct definition
`enum`	Enum definition
`impl`	Reserved syntax; Rue has no impl-block construct (6.0:1a)
`interface`	Interface declaration (6.8, `--preview interfaces`)
`self`	Self parameter in methods
`drop`	Destructor declaration
`pub`	Public visibility modifier
`const`	Constant declaration
`checked`	Checked block (§9.1)
`unchecked`	Unchecked function modifier
`ptr`	Pointer type constructor (`ptr const T` / `ptr mut T`)
`extern`	Foreign declaration block (`extern "C" { … }`, ADR-0064)
`yield`	Accessor body exit (`-> borrow T`/`-> inout T` accessors, ADR-0062)

Contextual Keywords

[2.4:2a]

A contextual keyword is an identifier that has special meaning only in a grammatical position that expects it and is an ordinary identifier everywhere else. is is a contextual keyword: it introduces a conformance list after a struct name or after the subject type of a freestanding conformance assertion (6.8:2), and it remains usable as the name of a binding, parameter, field, function, or method.

Type Names

[2.4:3]

The following are type names and are reserved:

Type	Description
`i8`	8-bit signed integer
`i16`	16-bit signed integer
`i32`	32-bit signed integer
`i64`	64-bit signed integer
`u8`	8-bit unsigned integer
`u16`	16-bit unsigned integer
`u32`	32-bit unsigned integer
`u64`	64-bit unsigned integer
`f32`	IEEE 754 binary32 floating-point (§3.12)
`f64`	IEEE 754 binary64 floating-point (§3.12)
`bool`	Boolean type
`type`	Compile-time type of types
`Self`	The enclosing struct type, within a struct block (§6.4)