## 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.

### Operators

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

Operator | Example | Explanation | Overloadable? |
---|---|---|---|

`!` | `ident!(...)` , `ident!{...}` , `ident![...]` | Macro expansion | |

`!` | `!expr` | Bitwise or logical complement | `Not` |

`!=` | `expr != expr` | Nonequality comparison | `PartialEq` |

`%` | `expr % expr` | Arithmetic remainder | `Rem` |

`%=` | `var %= expr` | Arithmetic remainder and assignment | `RemAssign` |

`&` | `&expr` , `&mut expr` | Borrow | |

`&` | `&type` , `&mut type` , `&'a type` , `&'a mut type` | Borrowed pointer type | |

`&` | `expr & expr` | Bitwise AND | `BitAnd` |

`&=` | `var &= expr` | Bitwise AND and assignment | `BitAndAssign` |

`&&` | `expr && expr` | Short-circuiting logical AND | |

`*` | `expr * expr` | Arithmetic multiplication | `Mul` |

`*=` | `var *= expr` | Arithmetic multiplication and assignment | `MulAssign` |

`*` | `*expr` | Dereference | `Deref` |

`*` | `*const type` , `*mut type` | Raw pointer | |

`+` | `trait + trait` , `'a + trait` | Compound type constraint | |

`+` | `expr + expr` | Arithmetic addition | `Add` |

`+=` | `var += expr` | Arithmetic addition and assignment | `AddAssign` |

`,` | `expr, expr` | Argument and element separator | |

`-` | `- expr` | Arithmetic negation | `Neg` |

`-` | `expr - expr` | Arithmetic subtraction | `Sub` |

`-=` | `var -= expr` | Arithmetic subtraction and assignment | `SubAssign` |

`->` | `fn(...) -> type` , `|...| -> type` | Function and closure return type | |

`.` | `expr.ident` | Member access | |

`..` | `..` , `expr..` , `..expr` , `expr..expr` | Right-exclusive range literal | `PartialOrd` |

`..=` | `..=expr` , `expr..=expr` | Right-inclusive range literal | `PartialOrd` |

`..` | `..expr` | Struct 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 / expr` | Arithmetic division | `Div` |

`/=` | `var /= expr` | Arithmetic division and assignment | `DivAssign` |

`:` | `pat: type` , `ident: type` | Constraints | |

`:` | `ident: expr` | Struct field initializer | |

`:` | `'a: loop {...}` | Loop label | |

`;` | `expr;` | Statement and item terminator | |

`;` | `[...; len]` | Part of fixed-size array syntax | |

`<<` | `expr << expr` | Left-shift | `Shl` |

`<<=` | `var <<= expr` | Left-shift and assignment | `ShlAssign` |

`<` | `expr < expr` | Less than comparison | `PartialOrd` |

`<=` | `expr <= expr` | Less than or equal to comparison | `PartialOrd` |

`=` | `var = expr` , `ident = type` | Assignment/equivalence | |

`==` | `expr == expr` | Equality comparison | `PartialEq` |

`=>` | `pat => expr` | Part of match arm syntax | |

`>` | `expr > expr` | Greater than comparison | `PartialOrd` |

`>=` | `expr >= expr` | Greater than or equal to comparison | `PartialOrd` |

`>>` | `expr >> expr` | Right-shift | `Shr` |

`>>=` | `var >>= expr` | Right-shift and assignment | `ShrAssign` |

`@` | `ident @ pat` | Pattern binding | |

`^` | `expr ^ expr` | Bitwise exclusive OR | `BitXor` |

`^=` | `var ^= expr` | Bitwise exclusive OR and assignment | `BitXorAssign` |

`|` | `pat | pat` | Pattern alternatives | |

`|` | `expr | expr` | Bitwise OR | `BitOr` |

`|=` | `var |= expr` | Bitwise OR and assignment | `BitOrAssign` |

`||` | `expr || expr` | Short-circuiting logical OR | |

`?` | `expr?` | Error propagation |

### Non-operator Symbols

The following list contains all symbols 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

Symbol | Explanation |
---|---|

`'ident` | Named 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 an array of bytes 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 |

`|...| expr` | Closure |

`!` | 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

Symbol | Explanation |
---|---|

`ident::ident` | Namespace path |

`::path` | Path relative to the crate root (i.e., an explicitly absolute path) |

`self::path` | Path relative to the current module (i.e., an explicitly relative path). |

`super::path` | Path relative to the parent of the current module |

`type::ident` , `<type as trait>::ident` | Associated 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

Symbol | Explanation |
---|---|

`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<...> type` | Higher-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

Symbol | Explanation |
---|---|

`T: U` | Generic parameter `T` constrained to types that implement `U` |

`T: 'a` | Generic type `T` must outlive lifetime `'a` (meaning the type cannot transitively contain any references with lifetimes shorter than `'a` ) |

`T: 'static` | Generic type `T` contains no borrowed references other than `'static` ones |

`'b: 'a` | Generic lifetime `'b` must outlive lifetime `'a` |

`T: ?Sized` | Allow generic type parameter to be a dynamically sized type |

`'a + trait` , `trait + trait` | Compound 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

Symbol | Explanation |
---|---|

`#[meta]` | Outer attribute |

`#![meta]` | Inner attribute |

`$ident` | Macro substitution |

`$ident:kind` | Macro capture |

`$(…)…` | Macro repetition |

`ident!(...)` , `ident!{...}` , `ident![...]` | Macro invocation |

Table B-7 shows symbols that create comments.

Table B-7: Comments

Symbol | Explanation |
---|---|

`//` | 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

Symbol | Explanation |
---|---|

`()` | 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 `struct` s 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

Context | Explanation |
---|---|

`{...}` | Block expression |

`Type {...}` | `struct` literal |

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

Table B-10: Square Brackets

Context | Explanation |
---|---|

`[...]` | 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” |