Appendix B: Operators and Symbols

This appendix contains a glossary of Rust’s syntax, including operators and other symbols that appear by themselves or in the context of paths, generics, trait bounds, macros, attributes, comments, tuples, and brackets.


Table B-1 contains the operators in Rust, an example of how the operator would appear in context, a short explanation, and whether that operator is overloadable. If an operator is overloadable, the relevant trait to use to overload that operator is listed.

Table B-1: Operators

!ident!(...), ident!{...}, ident![...]Macro expansion
!!exprBitwise or logical complementNot
!=var != exprNonequality comparisonPartialEq
%expr % exprArithmetic remainderRem
%=var %= exprArithmetic remainder and assignmentRemAssign
&&expr, &mut exprBorrow
&&type, &mut type, &'a type, &'a mut typeBorrowed pointer type
&expr & exprBitwise ANDBitAnd
&=var &= exprBitwise AND and assignmentBitAndAssign
&&expr && exprShort-circuiting logical AND
*expr * exprArithmetic multiplicationMul
*=var *= exprArithmetic multiplication and assignmentMulAssign
**const type, *mut typeRaw pointer
+trait + trait, 'a + traitCompound type constraint
+expr + exprArithmetic additionAdd
+=var += exprArithmetic addition and assignmentAddAssign
,expr, exprArgument and element separator
-- exprArithmetic negationNeg
-expr - exprArithmetic subtractionSub
-=var -= exprArithmetic subtraction and assignmentSubAssign
->fn(...) -> type, |...| -> typeFunction and closure return type
.expr.identMember access
...., expr.., ..expr, expr..exprRight-exclusive range literalPartialOrd
..=..=expr, expr..=exprRight-inclusive range literalPartialOrd
....exprStruct literal update syntax
..variant(x, ..), struct_type { x, .. }“And the rest” pattern binding
...expr...expr(Deprecated, use ..= instead) In a pattern: inclusive range pattern
/expr / exprArithmetic divisionDiv
/=var /= exprArithmetic division and assignmentDivAssign
:pat: type, ident: typeConstraints
:ident: exprStruct field initializer
:'a: loop {...}Loop label
;expr;Statement and item terminator
;[...; len]Part of fixed-size array syntax
<<expr << exprLeft-shiftShl
<<=var <<= exprLeft-shift and assignmentShlAssign
<expr < exprLess than comparisonPartialOrd
<=expr <= exprLess than or equal to comparisonPartialOrd
=var = expr, ident = typeAssignment/equivalence
==expr == exprEquality comparisonPartialEq
=>pat => exprPart of match arm syntax
>expr > exprGreater than comparisonPartialOrd
>=expr >= exprGreater than or equal to comparisonPartialOrd
>>expr >> exprRight-shiftShr
>>=var >>= exprRight-shift and assignmentShrAssign
@ident @ patPattern binding
^expr ^ exprBitwise exclusive ORBitXor
^=var ^= exprBitwise exclusive OR and assignmentBitXorAssign
|pat | patPattern alternatives
|expr | exprBitwise ORBitOr
|=var |= exprBitwise OR and assignmentBitOrAssign
||expr || exprShort-circuiting logical OR
?expr?Error propagation

Non-operator Symbols

The following list contains all non-letters that don’t function as operators; that is, they don’t behave like a function or method call.

Table B-2 shows symbols that appear on their own and are valid in a variety of locations.

Table B-2: Stand-Alone Syntax

'identNamed lifetime or loop label
...u8, ...i32, ...f64, ...usize, etc.Numeric literal of specific type
"..."String literal
r"...", r#"..."#, r##"..."##, etc.Raw string literal, escape characters not processed
b"..."Byte string literal; constructs a [u8] instead of a string
br"...", br#"..."#, br##"..."##, etc.Raw byte string literal, combination of raw and byte string literal
'...'Character literal
b'...'ASCII byte literal
|...| exprClosure
!Always empty bottom type for diverging functions
_“Ignored” pattern binding; also used to make integer literals readable

Table B-3 shows symbols that appear in the context of a path through the module hierarchy to an item.

Table B-3: Path-Related Syntax

ident::identNamespace path
::pathPath relative to the crate root (i.e., an explicitly absolute path)
self::pathPath relative to the current module (i.e., an explicitly relative path).
super::pathPath relative to the parent of the current module
type::ident, <type as trait>::identAssociated constants, functions, and types
<type>::...Associated item for a type that cannot be directly named (e.g., <&T>::..., <[T]>::..., etc.)
trait::method(...)Disambiguating a method call by naming the trait that defines it
type::method(...)Disambiguating a method call by naming the type for which it’s defined
<type as trait>::method(...)Disambiguating a method call by naming the trait and type

Table B-4 shows symbols that appear in the context of using generic type parameters.

Table B-4: Generics

path<...>Specifies parameters to generic type in a type (e.g., Vec<u8>)
path::<...>, method::<...>Specifies parameters to generic type, function, or method in an expression; often referred to as turbofish (e.g., "42".parse::<i32>())
fn ident<...> ...Define generic function
struct ident<...> ...Define generic structure
enum ident<...> ...Define generic enumeration
impl<...> ...Define generic implementation
for<...> typeHigher-ranked lifetime bounds
type<ident=type>A generic type where one or more associated types have specific assignments (e.g., Iterator<Item=T>)

Table B-5 shows symbols that appear in the context of constraining generic type parameters with trait bounds.

Table B-5: Trait Bound Constraints

T: UGeneric parameter T constrained to types that implement U
T: 'aGeneric type T must outlive lifetime 'a (meaning the type cannot transitively contain any references with lifetimes shorter than 'a)
T : 'staticGeneric type T contains no borrowed references other than 'static ones
'b: 'aGeneric lifetime 'b must outlive lifetime 'a
T: ?SizedAllow generic type parameter to be a dynamically sized type
'a + trait, trait + traitCompound type constraint

Table B-6 shows symbols that appear in the context of calling or defining macros and specifying attributes on an item.

Table B-6: Macros and Attributes

#[meta]Outer attribute
#![meta]Inner attribute
$identMacro substitution
$ident:kindMacro capture
$(…)…Macro repetition
ident!(...), ident!{...}, ident![...]Macro invocation

Table B-7 shows symbols that create comments.

Table B-7: Comments

//Line comment
//!Inner line doc comment
///Outer line doc comment
/*...*/Block comment
/*!...*/Inner block doc comment
/**...*/Outer block doc comment

Table B-8 shows symbols that appear in the context of using tuples.

Table B-8: Tuples

()Empty tuple (aka unit), both literal and type
(expr)Parenthesized expression
(expr,)Single-element tuple expression
(type,)Single-element tuple type
(expr, ...)Tuple expression
(type, ...)Tuple type
expr(expr, ...)Function call expression; also used to initialize tuple structs and tuple enum variants
expr.0, expr.1, etc.Tuple indexing

Table B-9 shows the contexts in which curly braces are used.

Table B-9: Curly Brackets

{...}Block expression
Type {...}struct literal

Table B-10 shows the contexts in which square brackets are used.

Table B-10: Square Brackets

[...]Array literal
[expr; len]Array literal containing len copies of expr
[type; len]Array type containing len instances of type
expr[expr]Collection indexing. Overloadable (Index, IndexMut)
expr[..], expr[a..], expr[..b], expr[a..b]Collection indexing pretending to be collection slicing, using Range, RangeFrom, RangeTo, or RangeFull as the “index”