附录 B: 运算符和符号
这个附录包含了一个 Rust 语法的词汇表，包括单独出现或在路径、泛型、特征边界、宏、属性、注释、元组和括号上下文中出现的运算符和其他符号。
运算符
表B-1 包含了Rust中的运算符，运算符在上下文中出现的示例，简短的解释，以及该运算符是否可重载。如果运算符是可重载的，将列出用于重载该运算符的相关特征。
表 B-1：运算符
| 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 | Field access | |
. | expr.ident(expr, ...) | Method call | |
. | expr.0, expr.1, and so on | Tuple indexing | |
.. | .., 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 |
非运算符符号
以下表格包含所有不作为运算符功能的符号；也就是说，它们的行为不像函数或方法调用。
表B-2显示了单独出现并在多种位置有效的符号。
表 B-2：独立语法
| Symbol | Explanation |
|---|---|
'ident | Named lifetime or loop label |
Digits immediately followed by u8, i32, f64, usize, and so on | Numeric literal of specific type |
"..." | String literal |
r"...", r#"..."#, r##"..."##, and so on | Raw string literal; escape characters not processed |
b"..." | Byte string literal; constructs an array of bytes instead of a string |
br"...", br#"..."#, br##"..."##, and so on | 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 |
表B-3显示了在通过模块层次结构到项的路径中出现的符号。
表 B-3：路径相关语法
| Symbol | Explanation |
|---|---|
ident::ident | Namespace path |
::path | Path relative to the crate root (that is, an explicitly absolute path) |
self::path | Path relative to the current module (that is, 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 (for example, <&T>::..., <[T]>::..., and so on) |
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 |
表B-4显示了在使用泛型类型参数的上下文中出现的符号。
表 B-4：泛型
| Symbol | Explanation |
|---|---|
path<...> | Specifies parameters to a generic type in a type (for example, Vec<u8>) |
path::<...>, method::<...> | Specifies parameters to a generic type, function, or method in an expression; often referred to as turbofish (for example, "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 (for example, Iterator<Item=T>) |
表B-5显示了在使用特征边界限制泛型类型参数时出现的符号。
表 B-5：特征边界约束
| 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 |
表B-6显示了在调用或定义宏以及在项上指定属性时出现的符号。
表 B-6：宏和属性
| Symbol | Explanation |
|---|---|
#[meta] | Outer attribute |
#![meta] | Inner attribute |
$ident | Macro substitution |
$ident:kind | Macro metavariable |
$(...)... | Macro repetition |
ident!(...), ident!{...}, ident![...] | Macro invocation |
表 B-7 显示了创建注释的符号。
表 B-7：注释
| Symbol | Explanation |
|---|---|
// | Line comment |
//! | Inner line doc comment |
/// | Outer line doc comment |
/*...*/ | Block comment |
/*!...*/ | Inner block doc comment |
/**...*/ | Outer block doc comment |
表B-8显示了使用括号的上下文。
表 B-8：括号
| 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 structs and tuple enum variants |
表B-9显示了使用大括号的上下文。
表 B-9：大括号
| Context | Explanation |
|---|---|
{...} | Block expression |
Type {...} | Struct literal |
表 B-10 显示了方括号使用的上下文。
表 B-10：方括号
| 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” |