Syntax Index - The Rust Programming Language

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# Syntax Index

## Keywords

- `as`: primitive casting, or disambiguating the specific trait containing an item. See Casting Between Types (`as`), Universal Function Call Syntax (Angle-bracket Form), Associated Types.
- `break`: break out of loop. See Loops (Ending Iteration Early).
- `const`: constant items and constant raw pointers. See `const` and `static`, Raw Pointers.
- `continue`: continue to next loop iteration. See Loops (Ending Iteration Early).
- `crate`: external crate linkage. See Crates and Modules (Importing External Crates).
- `else`: fallback for `if` and `if let` constructs. See `if`, `if let`.
- `enum`: defining enumeration. See Enums.
- `extern`: external crate, function, and variable linkage. See Crates and Modules (Importing External Crates), Foreign Function Interface.
- `false`: boolean false literal. See Primitive Types (Booleans).
- `fn`: function definition and function pointer types. See Functions.
- `for`: iterator loop, part of trait `impl` syntax, and higher-ranked lifetime syntax. See Loops (`for`), Method Syntax.
- `if`: conditional branching. See `if`, `if let`.
- `impl`: inherent and trait implementation blocks. See Method Syntax.
- `in`: part of `for` loop syntax. See Loops (`for`).
- `let`: variable binding. See Variable Bindings.
- `loop`: unconditional, infinite loop. See Loops (`loop`).
- `match`: pattern matching. See Match.
- `mod`: module declaration. See Crates and Modules (Defining Modules).
- `move`: part of closure syntax. See Closures (`move` closures).
- `mut`: denotes mutability in pointer types and pattern bindings. See Mutability.
- `pub`: denotes public visibility in `struct` fields, `impl` blocks, and modules. See Crates and Modules (Exporting a Public Interface).
- `ref`: by-reference binding. See Patterns (`ref` and `ref mut`).
- `return`: return from function. See Functions (Early Returns).
- `Self`: implementor type alias. See Traits.
- `self`: method subject. See Method Syntax (Method Calls).
- `static`: global variable. See `const` and `static` (`static`).
- `struct`: structure definition. See Structs.
- `trait`: trait definition. See Traits.
- `true`: boolean true literal. See Primitive Types (Booleans).
- `type`: type alias, and associated type definition. See `type` Aliases, Associated Types.
- `unsafe`: denotes unsafe code, functions, traits, and implementations. See Unsafe.
- `use`: import symbols into scope. See Crates and Modules (Importing Modules with `use`).
- `where`: type constraint clauses. See Traits (`where` clause).
- `while`: conditional loop. See Loops (`while`).

## Operators and Symbols

- `!` (`ident!(…)`, `ident!{…}`, `ident![…]`): denotes macro expansion. See Macros.
- `!` (`!expr`): bitwise or logical complement. Overloadable (`Not`).
- `!=` (`var != expr`): nonequality comparison. Overloadable (`PartialEq`).
- `%` (`expr % expr`): arithmetic remainder. Overloadable (`Rem`).
- `%=` (`var %= expr`): arithmetic remainder & assignment. Overloadable (`RemAssign`).
- `&` (`expr & expr`): bitwise and. Overloadable (`BitAnd`).
- `&` (`&expr`, `&mut expr`): borrow. See References and Borrowing.
- `&` (`&type`, `&mut type`, `&'a type`, `&'a mut type`): borrowed pointer type. See References and Borrowing.
- `&=` (`var &= expr`): bitwise and & assignment. Overloadable (`BitAndAssign`).
- `&&` (`expr && expr`): logical and.
- `*` (`expr * expr`): arithmetic multiplication. Overloadable (`Mul`).
- `*` (`*expr`): dereference.
- `*` (`*const type`, `*mut type`): raw pointer. See Raw Pointers.
- `*=` (`var *= expr`): arithmetic multiplication & assignment. Overloadable (`MulAssign`).
- `+` (`expr + expr`): arithmetic addition. Overloadable (`Add`).
- `+` (`trait + trait`, `'a + trait`): compound type constraint. See Traits (Multiple Trait Bounds).
- `+=` (`var += expr`): arithmetic addition & assignment. Overloadable (`AddAssign`).
- `,`: argument and element separator. See Attributes, Functions, Structs, Generics, Match, Closures, Crates and Modules (Importing Modules with `use`).
- `-` (`expr - expr`): arithmetic subtraction. Overloadable (`Sub`).
- `-` (`- expr`): arithmetic negation. Overloadable (`Neg`).
- `-=` (`var -= expr`): arithmetic subtraction & assignment. Overloadable (`SubAssign`).
- `->` (`fn(…) -> type`, `|…| -> type`): function and closure return type. See Functions, Closures.
- `.` (`expr.ident`): member access. See Structs, Method Syntax.
- `..` (`..`, `expr..`, `..expr`, `expr..expr`): right-exclusive range literal.
- `..` (`..expr`): struct literal update syntax. See Structs (Update syntax).
- `..` (`variant(x, ..)`, `struct_type { x, .. }`): "and the rest" pattern binding. See Patterns (Ignoring bindings).
- `...` (`...expr`, `expr...expr`) in an expression: inclusive range expression. See Iterators.
- `...` (`expr...expr`) in a pattern: inclusive range pattern. See Patterns (Ranges).
- `/` (`expr / expr`): arithmetic division. Overloadable (`Div`).
- `/=` (`var /= expr`): arithmetic division & assignment. Overloadable (`DivAssign`).
- `:` (`pat: type`, `ident: type`): constraints. See Variable Bindings, Functions, Structs, Traits.
- `:` (`ident: expr`): struct field initializer. See Structs.
- `:` (`'a: loop {…}`): loop label. See Loops (Loops Labels).
- `;`: statement and item terminator.
- `;` (`[…; len]`): part of fixed-size array syntax. See Primitive Types (Arrays).
- `<<` (`expr << expr`): left-shift. Overloadable (`Shl`).
- `<<=` (`var <<= expr`): left-shift & assignment. Overloadable (`ShlAssign`).
- `<` (`expr < expr`): less-than comparison. Overloadable (`PartialOrd`).
- `<=` (`var <= expr`): less-than or equal-to comparison. Overloadable (`PartialOrd`).
- `=` (`var = expr`, `ident = type`): assignment/equivalence. See Variable Bindings, `type` Aliases, generic parameter defaults.
- `==` (`var == expr`): equality comparison. Overloadable (`PartialEq`).
- `=>` (`pat => expr`): part of match arm syntax. See Match.
- `>` (`expr > expr`): greater-than comparison. Overloadable (`PartialOrd`).
- `>=` (`var >= expr`): greater-than or equal-to comparison. Overloadable (`PartialOrd`).
- `>>` (`expr >> expr`): right-shift. Overloadable (`Shr`).
- `>>=` (`var >>= expr`): right-shift & assignment. Overloadable (`ShrAssign`).
- `@` (`ident @ pat`): pattern binding. See Patterns (Bindings).
- `^` (`expr ^ expr`): bitwise exclusive or. Overloadable (`BitXor`).
- `^=` (`var ^= expr`): bitwise exclusive or & assignment. Overloadable (`BitXorAssign`).
- `|` (`expr | expr`): bitwise or. Overloadable (`BitOr`).
- `|` (`pat | pat`): pattern alternatives. See Patterns (Multiple patterns).
- `|` (`|…| expr`): closures. See Closures.
- `|=` (`var |= expr`): bitwise or & assignment. Overloadable (`BitOrAssign`).
- `||` (`expr || expr`): logical or.
- `_`: "ignored" pattern binding (see Patterns (Ignoring bindings)). Also used to make integer-literals readable (see Reference (Integer literals)).
- `?` (`expr?`): Error propagation. Returns early when `Err(_)` is encountered, unwraps otherwise. Similar to the `try!` macro.

## Other Syntax

- `'ident`: named lifetime or loop label. See Lifetimes, Loops (Loops Labels).
- `…u8`, `…i32`, `…f64`, `…usize`, …: numeric literal of specific type.
- `"…"`: string literal. See Strings.
- `r"…"`, `r#"…"#`, `r##"…"##`, …: raw string literal, escape characters are not processed. See Reference (Raw String Literals).
- `b"…"`: byte string literal, constructs a `[u8]` instead of a string. See Reference (Byte String Literals).
- `br"…"`, `br#"…"#`, `br##"…"##`, …: raw byte string literal, combination of raw and byte string literal. See Reference (Raw Byte String Literals).
- `'…'`: character literal. See Primitive Types (`char`).
- `b'…'`: ASCII byte literal.
- `|…| expr`: closure. See Closures.

- `ident::ident`: path. See Crates and Modules (Defining Modules).
- `::path`: path relative to the crate root (i.e. an explicitly absolute path). See Crates and Modules (Re-exporting with `pub use`).
- `self::path`: path relative to the current module (i.e. an explicitly relative path). See Crates and Modules (Re-exporting with `pub use`).
- `super::path`: path relative to the parent of the current module. See Crates and Modules (Re-exporting with `pub use`).
- `type::ident`, `<type as trait>::ident`: associated constants, functions, and types. See Associated Types.
- `<type>::…`: associated item for a type which cannot be directly named (e.g. `<&T>::…`, `<[T]>::…`, etc.). See Associated Types.
- `trait::method(…)`: disambiguating a method call by naming the trait which defines it. See Universal Function Call Syntax.
- `type::method(…)`: disambiguating a method call by naming the type for which it's defined. See Universal Function Call Syntax.
- `<type as trait>::method(…)`: disambiguating a method call by naming the trait and type. See Universal Function Call Syntax (Angle-bracket Form).

- `path<…>` (e.g. `Vec<u8>`): specifies parameters to generic type in a type. See Generics.
- `path::<…>`, `method::<…>` (e.g. `"42".parse::<i32>()`): specifies parameters to generic type, function, or method in an expression. See Generics § Resolving ambiguities.
- `fn ident<…> …`: define generic function. See Generics.
- `struct ident<…> …`: define generic structure. See Generics.
- `enum ident<…> …`: define generic enumeration. See Generics.
- `impl<…> …`: define generic implementation.
- `for<…> type`: higher-ranked lifetime bounds.
- `type<ident=type>` (e.g. `Iterator<Item=T>`): a generic type where one or more associated types have specific assignments. See Associated Types.

- `T: U`: generic parameter `T` constrained to types that implement `U`. See Traits.
- `T: 'a`: generic type `T` must outlive lifetime `'a`. When we say that a type 'outlives' the lifetime, we mean that it cannot transitively contain any references with lifetimes shorter than `'a`.
- `T : 'static`: The 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. See Unsized Types (`?Sized`).
- `'a + trait`, `trait + trait`: compound type constraint. See Traits (Multiple Trait Bounds).

- `#[meta]`: outer attribute. See Attributes.
- `#![meta]`: inner attribute. See Attributes.
- `$ident`: macro substitution. See Macros.
- `$ident:kind`: macro capture. See Macros.
- `$(…)…`: macro repetition. See Macros.

- `//`: line comment. See Comments.
- `//!`: inner line doc comment. See Comments.
- `///`: outer line doc comment. See Comments.
- `/*…*/`: block comment. See Comments.
- `/*!…*/`: inner block doc comment. See Comments.
- `/**…*/`: outer block doc comment. See Comments.

- `!`: always empty Never type. See Diverging Functions.

- `()`: empty tuple (a.k.a. unit), both literal and type.
- `(expr)`: parenthesized expression.
- `(expr,)`: single-element tuple expression. See Primitive Types (Tuples).
- `(type,)`: single-element tuple type. See Primitive Types (Tuples).
- `(expr, …)`: tuple expression. See Primitive Types (Tuples).
- `(type, …)`: tuple type. See Primitive Types (Tuples).
- `expr(expr, …)`: function call expression. Also used to initialize tuple `struct`s and tuple `enum` variants. See Functions.
- `ident!(…)`, `ident!{…}`, `ident![…]`: macro invocation. See Macros.
- `expr.0`, `expr.1`, …: tuple indexing. See Primitive Types (Tuple Indexing).

- `{…}`: block expression.
- `Type {…}`: `struct` literal. See Structs.

- `[…]`: array literal. See Primitive Types (Arrays).
- `[expr; len]`: array literal containing `len` copies of `expr`. See Primitive Types (Arrays).
- `[type; len]`: array type containing `len` instances of `type`. See Primitive Types (Arrays).
- `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`, `RangeFull` as the "index".