mirror of https://github.com/rust-lang/book
Carol (Nichols || Goulding)
parent
88563dca24
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d50521fc08
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@ -6,189 +6,199 @@ trait bounds, macros, attributes, comments, tuples, and brackets.
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### Operators
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The following list contains the operators in Rust, an example of how the
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operator would appear in context, a short explanation, and whether that
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operator is overloadable. If an operator is overloadable, the relevant trait to
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use to overload that operator is listed.
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Table B-1 contains the operators in Rust, an example of how the operator would
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appear in context, a short explanation, and whether that operator is
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overloadable. If an operator is overloadable, the relevant trait to use to
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overload that operator is listed.
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<span class="caption">Table B-1: Operators</span>
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* `!` (`ident!(...)`, `ident!{...}`, `ident![...]`): denotes macro
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expansion.
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* `!` (`!expr`): bitwise or logical complement. Overloadable (`Not`).
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* `!=` (`var != expr`): nonequality comparison. Overloadable (`PartialEq`).
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* `%` (`expr % expr`): arithmetic remainder. Overloadable (`Rem`).
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* `%=` (`var %= expr`): arithmetic remainder and assignment. Overloadable
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(`RemAssign`).
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* `&` (`&expr`, `&mut expr`): borrow.
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* `&` (`&type`, `&mut type`, `&'a type`, `&'a mut type`): borrowed pointer type.
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* `&` (`expr & expr`): bitwise AND. Overloadable (`BitAnd`).
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* `&=` (`var &= expr`): bitwise AND and assignment. Overloadable
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(`BitAndAssign`).
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* `&&` (`expr && expr`): logical AND.
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* `*` (`expr * expr`): arithmetic multiplication. Overloadable (`Mul`).
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* `*` (`*expr`): dereference.
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* `*` (`*const type`, `*mut type`): raw pointer.
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* `*=` (`var *= expr`): arithmetic multiplication and assignment. Overloadable
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(`MulAssign`).
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* `+` (`trait + trait`, `'a + trait`): compound type constraint.
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* `+` (`expr + expr`): arithmetic addition. Overloadable (`Add`).
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* `+=` (`var += expr`): arithmetic addition and assignment. Overloadable
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(`AddAssign`).
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* `,`: argument and element separator.
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* `-` (`- expr`): arithmetic negation. Overloadable (`Neg`).
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* `-` (`expr - expr`): arithmetic subtraction. Overloadable (`Sub`).
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* `-=` (`var -= expr`): arithmetic subtraction and assignment. Overloadable
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(`SubAssign`).
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* `->` (`fn(...) -> type`, `|...| -> type`): function and closure
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return type.
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* `.` (`expr.ident`): member access.
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* `..` (`..`, `expr..`, `..expr`, `expr..expr`): right-exclusive range literal.
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* `..` (`..expr`): struct literal update syntax.
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* `..` (`variant(x, ..)`, `struct_type { x, .. }`): “and the rest” pattern
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binding.
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* `...` (`expr...expr`) *in a pattern*: inclusive range pattern.
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* `/` (`expr / expr`): arithmetic division. Overloadable (`Div`).
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* `/=` (`var /= expr`): arithmetic division and assignment. Overloadable
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(`DivAssign`).
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* `:` (`pat: type`, `ident: type`): constraints.
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* `:` (`ident: expr`): struct field initializer.
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* `:` (`'a: loop {...}`): loop label.
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* `;`: statement and item terminator.
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* `;` (`[...; len]`): part of fixed-size array syntax
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* `<<` (`expr << expr`): left-shift. Overloadable (`Shl`).
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* `<<=` (`var <<= expr`): left-shift and assignment. Overloadable (`ShlAssign`).
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* `<` (`expr < expr`): less than comparison. Overloadable (`PartialOrd`).
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* `<=` (`expr <= expr`): less than or equal to comparison. Overloadable
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(`PartialOrd`).
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* `=` (`var = expr`, `ident = type`): assignment/equivalence.
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* `==` (`expr == expr`): equality comparison. Overloadable (`PartialEq`).
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* `=>` (`pat => expr`): part of match arm syntax.
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* `>` (`expr > expr`): greater than comparison. Overloadable (`PartialOrd`).
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* `>=` (`expr >= expr`): greater than or equal to comparison. Overloadable
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(`PartialOrd`).
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* `>>` (`expr >> expr`): right-shift. Overloadable (`Shr`).
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* `>>=` (`var >>= expr`): right-shift and assignment. Overloadable
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(`ShrAssign`).
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* `@` (`ident @ pat`): pattern binding.
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* `^` (`expr ^ expr`): bitwise exclusive OR. Overloadable (`BitXor`).
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* `^=` (`var ^= expr`): bitwise exclusive OR and assignment. Overloadable
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(`BitXorAssign`).
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* `|` (`pat | pat`): pattern alternatives.
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* `|` (`|…| expr`): closures.
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* `|` (`expr | expr`): bitwise OR. Overloadable (`BitOr`).
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* `|=` (`var |= expr`): bitwise OR and assignment. Overloadable (`BitOrAssign`).
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* `||` (`expr || expr`): logical OR.
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* `_`: “ignored” pattern binding. Also used to make integer literals readable.
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* `?` (`expr?`): error propagation.
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| Operator | Example | Explanation | Overloadable? |
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|----------|---------|-------------|---------------|
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| `!` | `ident!(...)`, `ident!{...}`, `ident![...]` | Macro expansion | |
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| `!` | `!expr` | Bitwise or logical complement | `Not` |
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| `!=` | `var != expr` | Nonequality comparison | `PartialEq` |
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| `%` | `expr % expr` | Arithmetic remainder | `Rem` |
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| `%=` | `var %= expr` | Arithmetic remainder and assignment | `RemAssign` |
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| `&` | `&expr`, `&mut expr` | Borrow | |
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| `&` | `&type`, `&mut type`, `&'a type`, `&'a mut type` | Borrowed pointer type | |
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| `&` | `expr & expr` | Bitwise AND | `BitAnd` |
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| `&=` | `var &= expr` | Bitwise AND and assignment | `BitAndAssign` |
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| `&&` | `expr && expr` | Logical AND | |
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| `*` | `expr * expr` | Arithmetic multiplication | `Mul` |
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| `*=` | `var *= expr` | Arithmetic multiplication and assignment | `MulAssign` |
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| `*` | `*expr` | Dereference | |
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| `*` | `*const type`, `*mut type` | Raw pointer | |
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| `+` | `trait + trait`, `'a + trait` | Compound type constraint | |
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| `+` | `expr + expr` | Arithmetic addition | `Add` |
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| `+=` | `var += expr` | Arithmetic addition and assignment | `AddAssign` |
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| `,` | `expr, expr` | Argument and element separator | |
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| `-` | `- expr` | Arithmetic negation | `Neg` |
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| `-` | `expr - expr` | Arithmetic subtraction | `Sub` |
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| `-=` | `var -= expr` | Arithmetic subtraction and assignment | `SubAssign` |
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| `->` | `fn(...) -> type`, <code>\|...\| -> type</code> | Function and closure return type | |
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| `.` | `expr.ident` | Member access | |
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| `..` | `..`, `expr..`, `..expr`, `expr..expr` | Right-exclusive range literal | |
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| `..` | `..expr` | Struct literal update syntax | |
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| `..` | `variant(x, ..)`, `struct_type { x, .. }` | “And the rest” pattern binding | |
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| `...` | `expr...expr` | In a pattern: inclusive range pattern | |
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| `/` | `expr / expr` | Arithmetic division | `Div` |
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| `/=` | `var /= expr` | Arithmetic division and assignment | `DivAssign` |
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| `:` | `pat: type`, `ident: type` | Constraints | |
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| `:` | `ident: expr` | Struct field initializer | |
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| `:` | `'a: loop {...}` | Loop label | |
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| `;` | `expr;` | Statement and item terminator | |
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| `;` | `[...; len]` | Part of fixed-size array syntax | |
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| `<<` | `expr << expr` | Left-shift | `Shl` |
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| `<<=` | `var <<= expr` | Left-shift and assignment | `ShlAssign` |
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| `<` | `expr < expr` | Less than comparison | `PartialOrd` |
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| `<=` | `expr <= expr` | Less than or equal to comparison | `PartialOrd` |
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| `=` | `var = expr`, `ident = type` | Assignment/equivalence | |
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| `==` | `expr == expr` | Equality comparison | `PartialEq` |
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| `=>` | `pat => expr` | Part of match arm syntax | |
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| `>` | `expr > expr` | Greater than comparison | `PartialOrd` |
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| `>=` | `expr >= expr` | Greater than or equal to comparison | `PartialOrd` |
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| `>>` | `expr >> expr` | Right-shift | `Shr` |
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| `>>=` | `var >>= expr` | Right-shift and assignment | `ShrAssign` |
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| `@` | `ident @ pat` | Pattern binding | |
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| `^` | `expr ^ expr` | Bitwise exclusive OR | `BitXor` |
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| `^=` | `var ^= expr` | Bitwise exclusive OR and assignment | `BitXorAssign` |
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| <code>\|</code> | <code>pat \| pat</code> | Pattern alternatives | |
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| <code>\|</code> | <code>expr \| expr</code> | Bitwise OR | `BitOr` |
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| <code>\|=</code> | <code>var \|= expr</code> | Bitwise OR and assignment | `BitOrAssign` |
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| <code>\|\|</code> | <code>expr \|\| expr</code> | Logical OR | |
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| `?` | `expr?` | Error propagation | |
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### Non-operator Symbols
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The following list contains all non-letters that don’t function as operators;
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that is, they don’t behave like a function or method call.
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#### Stand-Alone Syntax
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Table B-2 shows symbols that appear on their own and are valid in a variety of
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locations.
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* `'ident`: named lifetime or loop label.
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* `...u8`, `...i32`, `...f64`, `...usize`, *etc.*: numeric literal of
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specific type.
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* `"..."`: string literal.
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* `r"..."`, `r#"..."#`, `r##"..."##`, *etc.*: raw string literal,
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escape characters are not processed.
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* `b"..."`: byte string literal, constructs a `[u8]` instead of a string.
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* `br"..."`, `br#"..."#`, `br##"..."##`, *etc.*: raw byte string
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literal, combination of raw and byte string literal.
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* `'...'`: character literal.
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* `b'...'`: ASCII byte literal.
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* `|...| expr`: closure.
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* `!`: always empty bottom type for diverging functions.
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<span class="caption">Table B-2: Stand-Alone Syntax</span>
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#### Path-Related Syntax
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| Symbol | Explanation |
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|--------|-------------|
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| `'ident` | Named lifetime or loop label |
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| `...u8`, `...i32`, `...f64`, `...usize`, etc. | Numeric literal of specific type |
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| `"..."` | String literal |
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| `r"..."`, `r#"..."#`, `r##"..."##`, etc. | Raw string literal, escape characters not processed |
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| `b"..."` | Byte string literal; constructs a `[u8]` instead of a string |
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| `br"..."`, `br#"..."#`, `br##"..."##`, etc. | Raw byte string literal, combination of raw and byte string literal |
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| `'...'` | Character literal |
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| `b'...'` | ASCII byte literal |
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| <code>\|...\| expr</code> | Closure |
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| `!` | Always empty bottom type for diverging functions |
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| `_` | “Ignored” pattern binding; also used to make integer literals readable |
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* `ident::ident`: namespace path.
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* `::path`: path relative to the crate root (*i.e.*, an explicitly absolute
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path).
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* `self::path`: path relative to the current module (*i.e.*, an explicitly
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relative path).
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* `super::path`: path relative to the parent of the current module.
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* `type::ident`, `<type as trait>::ident`: associated constants, functions, and
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types.
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* `<type>::...`: associated item for a type that cannot be directly named
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(*e.g.*, `<&T>::...`, `<[T]>::...`, *etc.*).
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* `trait::method(...)`: disambiguating a method call by naming the trait
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that defines it.
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* `type::method(...)`: disambiguating a method call by naming the type for
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which it’s defined.
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* `<type as trait>::method(...)`: disambiguating a method call by naming
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the trait *and* type.
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Table B-3 shows symbols that appear in the context of a path through the module
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hierarchy to an item.
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#### Generics
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<span class="caption">Table B-3: Path-Related Syntax</span>
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* `path<...>` (*e.g.*, `Vec<u8>`): specifies parameters to generic type *in
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a type*.
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* `path::<...>`, `method::<...>` (*e.g.*, `"42".parse::<i32>()`):
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specifies parameters to generic type, function, or method *in an expression*.
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Often referred to as *turbofish*.
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* `fn ident<...> ...`: define generic function.
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* `struct ident<...> ...`: define generic structure.
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* `enum ident<...> ...`: define generic enumeration.
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* `impl<...> ...`: define generic implementation.
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* `for<...> type`: higher-ranked lifetime bounds.
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* `type<ident=type>` (*e.g.*, `Iterator<Item=T>`): a generic type where one or
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more associated types have specific assignments.
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| Symbol | Explanation |
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|--------|-------------|
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| `ident::ident` | Namespace path |
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| `::path` | Path relative to the crate root (i.e., an explicitly absolute path) |
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| `self::path` | Path relative to the current module (i.e., an explicitly relative path).
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| `super::path` | Path relative to the parent of the current module |
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| `type::ident`, `<type as trait>::ident` | Associated constants, functions, and types |
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| `<type>::...` | Associated item for a type that cannot be directly named (e.g., `<&T>::...`, `<[T]>::...`, etc.) |
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| `trait::method(...)` | Disambiguating a method call by naming the trait that defines it |
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| `type::method(...)` | Disambiguating a method call by naming the type for which it’s defined |
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| `<type as trait>::method(...)` | Disambiguating a method call by naming the trait and type |
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#### Trait Bound Constraints
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Table B-4 shows symbols that appear in the context of using generic type
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parameters.
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* `T: U`: generic parameter `T` constrained to types that implement `U`.
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* `T: 'a`: generic type `T` must outlive lifetime `'a`. When we say that a type
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“outlives” the lifetime, we mean it cannot transitively contain any references
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with lifetimes shorter than `'a`.
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* `T : 'static`: the generic type `T` contains no borrowed references other
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than `'static` ones.
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* `'b: 'a`: generic lifetime `'b` must outlive lifetime `'a`.
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* `T: ?Sized`: allow generic type parameter to be a dynamically sized type.
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* `'a + trait`, `trait + trait`: compound type constraint.
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<span class="caption">Table B-4: Generics</span>
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#### Macros and Attributes
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| Symbol | Explanation |
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|--------|-------------|
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| `path<...>` | Specifies parameters to generic type in a type (e.g., `Vec<u8>`) |
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| `path::<...>`, `method::<...>` | Specifies parameters to generic type, function, or method in an expression; often referred to as turbofish (e.g., `"42".parse::<i32>()`) |
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| `fn ident<...> ...` | Define generic function |
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| `struct ident<...> ...` | Define generic structure |
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| `enum ident<...> ...` | Define generic enumeration |
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| `impl<...> ...` | Define generic implementation |
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| `for<...> type` | Higher-ranked lifetime bounds |
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| `type<ident=type>` | A generic type where one or more associated types have specific assignments (e.g., `Iterator<Item=T>`) |
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* `#[meta]`: outer attribute.
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* `#![meta]`: inner attribute.
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* `$ident`: macro substitution.
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* `$ident:kind`: macro capture.
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* `$(…)…`: macro repetition.
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Table B-5 shows symbols that appear in the context of constraining generic type
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parameters with trait bounds.
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#### Comments
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<span class="caption">Table B-5: Trait Bound Constraints</span>
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* `//`: line comment.
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* `//!`: inner line doc comment.
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* `///`: outer line doc comment.
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* `/*...*/`: block comment.
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* `/*!...*/`: inner block doc comment.
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* `/**...*/`: outer block doc comment.
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| Symbol | Explanation |
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|--------|-------------|
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| `T: U` | Generic parameter `T` constrained to types that implement `U` |
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| `T: 'a` | Generic type `T` must outlive lifetime `'a` (meaning the type cannot transitively contain any references with lifetimes shorter than `'a`) |
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| `T : 'static` | Generic type `T` contains no borrowed references other than `'static` ones |
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| `'b: 'a` | Generic lifetime `'b` must outlive lifetime `'a` |
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| `T: ?Sized` | Allow generic type parameter to be a dynamically sized type |
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| `'a + trait`, `trait + trait` | Compound type constraint |
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#### Tuples
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Table B-6 shows symbols that appear in the context of calling or defining
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macros and specifying attributes on an item.
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* `()`: empty tuple (*aka* unit), both literal and type.
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* `(expr)`: parenthesized expression.
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* `(expr,)`: single-element tuple expression.
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* `(type,)`: single-element tuple type.
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* `(expr, ...)`: tuple expression.
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* `(type, ...)`: tuple type.
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* `expr(expr, ...)`: function call expression. Also used to initialize
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tuple `struct`s and tuple `enum` variants.
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* `ident!(...)`, `ident!{...}`, `ident![...]`: macro invocation.
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* `expr.0`, `expr.1`, *etc.*: tuple indexing.
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<span class="caption">Table B-6: Macros and Attributes</span>
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#### Curly Brackets
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| Symbol | Explanation |
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|--------|-------------|
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| `#[meta]` | Outer attribute |
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| `#![meta]` | Inner attribute |
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| `$ident` | Macro substitution |
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| `$ident:kind` | Macro capture |
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| `$(…)…` | Macro repetition |
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* `{...}`: block expression.
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* `Type {...}`: `struct` literal.
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Table B-7 shows symbols that create comments.
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#### Square Brackets
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<span class="caption">Table B-7: Comments</span>
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* `[...]`: array literal.
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* `[expr; len]`: array literal containing `len` copies of `expr`.
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* `[type; len]`: array type containing `len` instances of `type`.
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* `expr[expr]`: collection indexing. Overloadable (`Index`, `IndexMut`).
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* `expr[..]`, `expr[a..]`, `expr[..b]`, `expr[a..b]`: collection indexing
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pretending to be collection slicing, using `Range`, `RangeFrom`, `RangeTo`, or
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`RangeFull` as the “index.”
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| Symbol | Explanation |
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|--------|-------------|
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| `//` | Line comment |
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| `//!` | Inner line doc comment |
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| `///` | Outer line doc comment |
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| `/*...*/` | Block comment |
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| `/*!...*/` | Inner block doc comment |
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| `/**...*/` | Outer block doc comment |
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Table B-8 shows symbols that appear in the context of using tuples.
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<span class="caption">Table B-8: Tuples</span>
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| Symbol | Explanation |
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|--------|-------------|
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| `()` | Empty tuple (aka unit), both literal and type |
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| `(expr)` | Parenthesized expression |
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| `(expr,)` | Single-element tuple expression |
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| `(type,)` | Single-element tuple type |
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| `(expr, ...)` | Tuple expression |
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| `(type, ...)` | Tuple type |
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| `expr(expr, ...)` | Function call expression; also used to initialize tuple `struct`s and tuple `enum` variants |
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| `ident!(...)`, `ident!{...}`, `ident![...]` | Macro invocation |
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| `expr.0`, `expr.1`, etc. | Tuple indexing |
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Table B-9 shows the contexts in which curly braces are used.
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<span class="caption">Table B-9: Curly Brackets</span>
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| Context | Explanation |
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|---------|-------------|
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| `{...}` | Block expression |
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| `Type {...}` | `struct` literal |
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Table B-10 shows the contexts in which square brackets are used.
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<span class="caption">Table B-10: Square Brackets</span>
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|
||||
| 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” |
|
||||
|
|
|
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Reference in New Issue