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3 /// Cast between types, or rename an import.
5 /// `as` is most commonly used to turn primitive types into other primitive types, but it has other
6 /// uses that include turning pointers into addresses, addresses into pointers, and pointers into
10 /// let thing1: u8 = 89.0 as u8;
11 /// assert_eq!('B' as u32, 66);
12 /// assert_eq!(thing1 as char, 'Y');
13 /// let thing2: f32 = thing1 as f32 + 10.5;
14 /// assert_eq!(true as u8 + thing2 as u8, 100);
17 /// In general, any cast that can be performed via ascribing the type can also be done using `as`,
18 /// so instead of writing `let x: u32 = 123`, you can write `let x = 123 as u32` (Note: `let x: u32
19 /// = 123` would be best in that situation). The same is not true in the other direction, however,
20 /// explicitly using `as` allows a few more coercions that aren't allowed implicitly, such as
21 /// changing the type of a raw pointer or turning closures into raw pointers.
23 /// Other places `as` is used include as extra syntax for [`crate`] and `use`, to change the name
24 /// something is imported as.
26 /// For more information on what `as` is capable of, see the [Reference]
28 /// [Reference]: ../reference/expressions/operator-expr.html#type-cast-expressions
29 /// [`crate`]: keyword.crate.html
32 #[doc(keyword = "break")]
34 /// Exit early from a loop.
36 /// When `break` is encountered, execution of the associated loop body is
37 /// immediately terminated.
49 /// assert_eq!(last, 12);
50 /// println!("{}", last);
53 /// A break expression is normally associated with the innermost loop enclosing the
54 /// `break` but a label can be used to specify which enclosing loop is affected.
57 /// 'outer: for i in 1..=5 {
58 /// println!("outer iteration (i): {}", i);
60 /// '_inner: for j in 1..=200 {
61 /// println!(" inner iteration (j): {}", j);
63 /// // breaks from inner loop, let's outer loop continue.
67 /// // breaks from outer loop, and directly to "Bye".
75 /// When associated with `loop`, a break expression may be used to return a value from that loop.
76 /// This is only valid with `loop` and not with any other type of loop.
77 /// If no value is specified, `break;` returns `()`.
78 /// Every `break` within a loop must return the same type.
81 /// let (mut a, mut b) = (1, 1);
82 /// let result = loop {
90 /// // first number in Fibonacci sequence over 10:
91 /// assert_eq!(result, 13);
92 /// println!("{}", result);
95 /// For more details consult the [Reference on "break expression"] and the [Reference on "break and
98 /// [Reference on "break expression"]: ../reference/expressions/loop-expr.html#break-expressions
99 /// [Reference on "break and loop values"]:
100 /// ../reference/expressions/loop-expr.html#break-and-loop-values
102 mod break_keyword { }
104 #[doc(keyword = "const")]
106 /// Compile-time constants and deterministic functions.
108 /// Sometimes a certain value is used many times throughout a program, and it can become
109 /// inconvenient to copy it over and over. What's more, it's not always possible or desirable to
110 /// make it a variable that gets carried around to each function that needs it. In these cases, the
111 /// `const` keyword provides a convenient alternative to code duplication.
114 /// const THING: u32 = 0xABAD1DEA;
116 /// let foo = 123 + THING;
119 /// Constants must be explicitly typed, unlike with `let` you can't ignore its type and let the
120 /// compiler figure it out. Any constant value can be defined in a const, which in practice happens
121 /// to be most things that would be reasonable to have a constant (barring `const fn`s). For
122 /// example, you can't have a File as a `const`.
124 /// The only lifetime allowed in a constant is `'static`, which is the lifetime that encompasses
125 /// all others in a Rust program. For example, if you wanted to define a constant string, it would
129 /// const WORDS: &'static str = "hello rust!";
132 /// Thanks to static lifetime elision, you usually don't have to explicitly use 'static:
135 /// const WORDS: &str = "hello convenience!";
138 /// `const` items looks remarkably similar to `static` items, which introduces some confusion as
139 /// to which one should be used at which times. To put it simply, constants are inlined wherever
140 /// they're used, making using them identical to simply replacing the name of the const with its
141 /// value. Static variables on the other hand point to a single location in memory, which all
142 /// accesses share. This means that, unlike with constants, they can't have destructors, and act as
143 /// a single value across the entire codebase.
145 /// Constants, as with statics, should always be in SCREAMING_SNAKE_CASE.
147 /// The `const` keyword is also used in raw pointers in combination with `mut`, as seen in `*const
148 /// T` and `*mut T`. More about that can be read at the [pointer] primitive part of the Rust docs.
150 /// For more detail on `const`, see the [Rust Book] or the [Reference]
152 /// [pointer]: primitive.pointer.html
154 /// ../book/ch03-01-variables-and-mutability.html#differences-between-variables-and-constants
155 /// [Reference]: ../reference/items/constant-items.html
156 mod const_keyword { }
158 #[doc(keyword = "continue")]
160 /// Skip to the next iteration of a loop.
162 /// When `continue` is encountered, the current iteration is terminated, returning control to the
163 /// loop head, typically continuing with the next iteration.
166 /// // Printing odd numbers by skipping even ones
167 /// for number in 1..=10 {
168 /// if number % 2 == 0 {
171 /// println!("{}", number);
175 /// Like `break`, `continue` is normally associated with the innermost enclosing loop, but labels
176 /// may be used to specify the affected loop.
179 /// // Print Odd numbers under 30 with unit <= 5
180 /// 'tens: for ten in 0..3 {
181 /// '_units: for unit in 0..=9 {
182 /// if unit % 2 == 0 {
188 /// println!("{}", ten * 10 + unit);
193 /// See [continue expressions] from the reference for more details.
195 /// [continue expressions]: ../reference/expressions/loop-expr.html#continue-expressions
196 mod continue_keyword { }
198 #[doc(keyword = "crate")]
200 /// A Rust binary or library.
202 /// The primary use of the `crate` keyword is as a part of `extern crate` declarations, which are
203 /// used to specify a dependency on a crate external to the one it's declared in. Crates are the
204 /// fundamental compilation unit of Rust code, and can be seen as libraries or projects. More can
205 /// be read about crates in the [Reference].
208 /// extern crate rand;
209 /// extern crate my_crate as thing;
210 /// extern crate std; // implicitly added to the root of every Rust project
213 /// The `as` keyword can be used to change what the crate is referred to as in your project. If a
214 /// crate name includes a dash, it is implicitly imported with the dashes replaced by underscores.
216 /// `crate` can also be used as in conjunction with `pub` to signify that the item it's attached to
217 /// is public only to other members of the same crate it's in.
220 /// # #[allow(unused_imports)]
221 /// pub(crate) use std::io::Error as IoError;
222 /// pub(crate) enum CoolMarkerType { }
223 /// pub struct PublicThing {
224 /// pub(crate) semi_secret_thing: bool,
228 /// `crate` is also used to represent the absolute path of a module, where `crate` refers to the
229 /// root of the current crate. For instance, `crate::foo::bar` refers to the name `bar` inside the
230 /// module `foo`, from anywhere else in the same crate.
232 /// [Reference]: ../reference/items/extern-crates.html
233 mod crate_keyword { }
235 #[doc(keyword = "else")]
237 /// What to do when an [`if`] condition does not hold.
239 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
241 /// [`if`]: keyword.if.html
242 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
245 #[doc(keyword = "enum")]
247 /// A type that can be any one of several variants.
249 /// Enums in Rust are similar to those of other compiled languages like C, but have important
250 /// differences that make them considerably more powerful. What Rust calls enums are more commonly
251 /// known as [Algebraic Data Types][ADT] if you're coming from a functional programming background.
252 /// The important detail is that each enum variant can have data to go along with it.
256 /// enum SimpleEnum {
268 /// enum ComplexEnum {
272 /// usual_struct_stuff: bool,
277 /// enum EmptyEnum { }
280 /// The first enum shown is the usual kind of enum you'd find in a C-style language. The second
281 /// shows off a hypothetical example of something storing location data, with `Coord` being any
282 /// other type that's needed, for example a struct. The third example demonstrates the kind of
283 /// data a variant can store, ranging from nothing, to a tuple, to an anonymous struct.
285 /// Instantiating enum variants involves explicitly using the enum's name as its namespace,
286 /// followed by one of its variants. `SimpleEnum::SecondVariant` would be an example from above.
287 /// When data follows along with a variant, such as with rust's built-in [`Option`] type, the data
288 /// is added as the type describes, for example `Option::Some(123)`. The same follows with
289 /// struct-like variants, with things looking like `ComplexEnum::LotsOfThings { usual_struct_stuff:
290 /// true, blah: "hello!".to_string(), }`. Empty Enums are similar to () in that they cannot be
291 /// instantiated at all, and are used mainly to mess with the type system in interesting ways.
293 /// For more information, take a look at the [Rust Book] or the [Reference]
295 /// [ADT]: https://en.wikipedia.org/wiki/Algebraic_data_type
296 /// [`Option`]: option/enum.Option.html
297 /// [Rust Book]: ../book/ch06-01-defining-an-enum.html
298 /// [Reference]: ../reference/items/enumerations.html
301 #[doc(keyword = "extern")]
303 /// Link to or import external code.
305 /// The `extern` keyword is used in two places in Rust. One is in conjunction with the [`crate`]
306 /// keyword to make your Rust code aware of other Rust crates in your project, i.e., `extern crate
307 /// lazy_static;`. The other use is in foreign function interfaces (FFI).
309 /// `extern` is used in two different contexts within FFI. The first is in the form of external
310 /// blocks, for declaring function interfaces that Rust code can call foreign code by.
313 /// #[link(name = "my_c_library")]
315 /// fn my_c_function(x: i32) -> bool;
319 /// This code would attempt to link with `libmy_c_library.so` on unix-like systems and
320 /// `my_c_library.dll` on Windows at runtime, and panic if it can't find something to link to. Rust
321 /// code could then use `my_c_function` as if it were any other unsafe Rust function. Working with
322 /// non-Rust languages and FFI is inherently unsafe, so wrappers are usually built around C APIs.
324 /// The mirror use case of FFI is also done via the `extern` keyword:
328 /// pub extern fn callable_from_c(x: i32) -> bool {
333 /// If compiled as a dylib, the resulting .so could then be linked to from a C library, and the
334 /// function could be used as if it was from any other library.
336 /// For more information on FFI, check the [Rust book] or the [Reference].
339 /// ../book/ch19-01-unsafe-rust.html#using-extern-functions-to-call-external-code
340 /// [Reference]: ../reference/items/external-blocks.html
341 mod extern_keyword { }
343 #[doc(keyword = "false")]
345 /// A value of type [`bool`] representing logical **false**.
347 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
349 /// [`bool`]: primitive.bool.html
350 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
351 mod false_keyword { }
353 #[doc(keyword = "fn")]
355 /// A function or function pointer.
357 /// Functions are the primary way code is executed within Rust. Function blocks, usually just
358 /// called functions, can be defined in a variety of different places and be assigned many
359 /// different attributes and modifiers.
361 /// Standalone functions that just sit within a module not attached to anything else are common,
362 /// but most functions will end up being inside [`impl`] blocks, either on another type itself, or
363 /// as a trait impl for that type.
366 /// fn standalone_function() {
370 /// pub fn public_thing(argument: bool) -> String {
380 /// pub fn new() -> Self {
388 /// In addition to presenting fixed types in the form of `fn name(arg: type, ..) -> return_type`,
389 /// functions can also declare a list of type parameters along with trait bounds that they fall
393 /// fn generic_function<T: Clone>(x: T) -> (T, T, T) {
394 /// (x.clone(), x.clone(), x.clone())
397 /// fn generic_where<T>(x: T) -> T
398 /// where T: std::ops::Add<Output = T> + Copy
404 /// Declaring trait bounds in the angle brackets is functionally identical to using a `where`
405 /// clause. It's up to the programmer to decide which works better in each situation, but `where`
406 /// tends to be better when things get longer than one line.
408 /// Along with being made public via `pub`, `fn` can also have an [`extern`] added for use in
411 /// For more information on the various types of functions and how they're used, consult the [Rust
412 /// book] or the [Reference].
414 /// [`impl`]: keyword.impl.html
415 /// [`extern`]: keyword.extern.html
416 /// [Rust book]: ../book/ch03-03-how-functions-work.html
417 /// [Reference]: ../reference/items/functions.html
420 #[doc(keyword = "for")]
422 /// Iteration with [`in`], trait implementation with [`impl`], or [higher-ranked trait bounds]
425 /// The `for` keyword is used in many syntactic locations:
427 /// * `for` is used in for-in-loops (see below).
428 /// * `for` is used when implementing traits as in `impl Trait for Type` (see [`impl`] for more info
430 /// * `for` is also used for [higher-ranked trait bounds] as in `for<'a> &'a T: PartialEq<i32>`.
432 /// for-in-loops, or to be more precise, iterator loops, are a simple syntactic sugar over a common
433 /// practice within Rust, which is to loop over an iterator until that iterator returns `None` (or
434 /// `break` is called).
438 /// println!("{}", i * 2);
441 /// for i in std::iter::repeat(5) {
442 /// println!("turns out {} never stops being 5", i);
443 /// break; // would loop forever otherwise
446 /// 'outer: for x in 5..50 {
455 /// As shown in the example above, `for` loops (along with all other loops) can be tagged, using
456 /// similar syntax to lifetimes (only visually similar, entirely distinct in practice). Giving the
457 /// same tag to `break` breaks the tagged loop, which is useful for inner loops. It is definitely
460 /// A `for` loop expands as shown:
464 /// # let iterator = 0..2;
465 /// for loop_variable in iterator {
472 /// # let iterator = 0..2;
474 /// let mut _iter = std::iter::IntoIterator::into_iter(iterator);
476 /// match _iter.next() {
477 /// Some(loop_variable) => {
486 /// More details on the functionality shown can be seen at the [`IntoIterator`] docs.
488 /// For more information on for-loops, see the [Rust book] or the [Reference].
490 /// [`in`]: keyword.in.html
491 /// [`impl`]: keyword.impl.html
492 /// [higher-ranked trait bounds]: ../reference/trait-bounds.html#higher-ranked-trait-bounds
493 /// [`IntoIterator`]: iter/trait.IntoIterator.html
495 /// ../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
496 /// [Reference]: ../reference/expressions/loop-expr.html#iterator-loops
499 #[doc(keyword = "if")]
501 /// Evaluate a block if a condition holds.
503 /// `if` is a familiar construct to most programmers, and is the main way you'll often do logic in
504 /// your code. However, unlike in most languages, `if` blocks can also act as expressions.
507 /// # let rude = true;
509 /// println!("whoops, mathematics broke");
511 /// println!("everything's fine!");
514 /// let greeting = if rude {
520 /// if let Ok(x) = "123".parse::<i32>() {
521 /// println!("{} double that and you get {}!", greeting, x * 2);
525 /// Shown above are the three typical forms an `if` block comes in. First is the usual kind of
526 /// thing you'd see in many languages, with an optional `else` block. Second uses `if` as an
527 /// expression, which is only possible if all branches return the same type. An `if` expression can
528 /// be used everywhere you'd expect. The third kind of `if` block is an `if let` block, which
529 /// behaves similarly to using a `match` expression:
532 /// if let Some(x) = Some(123) {
536 /// // something else
539 /// match Some(123) {
545 /// // something else
550 /// Each kind of `if` expression can be mixed and matched as needed.
553 /// if true == false {
554 /// println!("oh no");
555 /// } else if "something" == "other thing" {
556 /// println!("oh dear");
557 /// } else if let Some(200) = "blarg".parse::<i32>().ok() {
558 /// println!("uh oh");
560 /// println!("phew, nothing's broken");
564 /// The `if` keyword is used in one other place in Rust, namely as a part of pattern matching
565 /// itself, allowing patterns such as `Some(x) if x > 200` to be used.
567 /// For more information on `if` expressions, see the [Rust book] or the [Reference].
569 /// [Rust book]: ../book/ch03-05-control-flow.html#if-expressions
570 /// [Reference]: ../reference/expressions/if-expr.html
573 #[doc(keyword = "impl")]
575 /// Implement some functionality for a type.
577 /// The `impl` keyword is primarily used to define implementations on types. Inherent
578 /// implementations are standalone, while trait implementations are used to implement traits for
579 /// types, or other traits.
581 /// Functions and consts can both be defined in an implementation. A function defined in an
582 /// `impl` block can be standalone, meaning it would be called like `Foo::bar()`. If the function
583 /// takes `self`, `&self`, or `&mut self` as its first argument, it can also be called using
584 /// method-call syntax, a familiar feature to any object oriented programmer, like `foo.bar()`.
593 /// println!("boo! Example::boo() was called!");
596 /// fn answer(&mut self) {
597 /// self.number += 42;
600 /// fn get_number(&self) -> i32 {
606 /// fn do_thingy(&self);
609 /// impl Thingy for Example {
610 /// fn do_thingy(&self) {
611 /// println!("doing a thing! also, number is {}!", self.number);
616 /// For more information on implementations, see the [Rust book][book1] or the [Reference].
618 /// The other use of the `impl` keyword is in `impl Trait` syntax, which can be seen as a shorthand
619 /// for "a concrete type that implements this trait". Its primary use is working with closures,
620 /// which have type definitions generated at compile time that can't be simply typed out.
623 /// fn thing_returning_closure() -> impl Fn(i32) -> bool {
624 /// println!("here's a closure for you!");
625 /// |x: i32| x % 3 == 0
629 /// For more information on `impl Trait` syntax, see the [Rust book][book2].
631 /// [book1]: ../book/ch05-03-method-syntax.html
632 /// [Reference]: ../reference/items/implementations.html
633 /// [book2]: ../book/ch10-02-traits.html#returning-types-that-implement-traits
636 #[doc(keyword = "in")]
638 /// Iterate over a series of values with [`for`].
640 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
642 /// [`for`]: keyword.for.html
643 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
646 #[doc(keyword = "let")]
648 /// Bind a value to a variable.
650 /// The primary use for the `let` keyword is in `let` statements, which are used to introduce a new
651 /// set of variables into the current scope, as given by a pattern.
654 /// # #![allow(unused_assignments)]
655 /// let thing1: i32 = 100;
656 /// let thing2 = 200 + thing1;
658 /// let mut changing_thing = true;
659 /// changing_thing = false;
661 /// let (part1, part2) = ("first", "second");
668 /// let Example { a, b: _ } = Example {
675 /// The pattern is most commonly a single variable, which means no pattern matching is done and
676 /// the expression given is bound to the variable. Apart from that, patterns used in `let` bindings
677 /// can be as complicated as needed, given that the pattern is exhaustive. See the [Rust
678 /// book][book1] for more information on pattern matching. The type of the pattern is optionally
679 /// given afterwards, but if left blank is automatically inferred by the compiler if possible.
681 /// Variables in Rust are immutable by default, and require the `mut` keyword to be made mutable.
683 /// Multiple variables can be defined with the same name, known as shadowing. This doesn't affect
684 /// the original variable in any way beyond being unable to directly access it beyond the point of
685 /// shadowing. It continues to remain in scope, getting dropped only when it falls out of scope.
686 /// Shadowed variables don't need to have the same type as the variables shadowing them.
689 /// let shadowing_example = true;
690 /// let shadowing_example = 123.4;
691 /// let shadowing_example = shadowing_example as u32;
692 /// let mut shadowing_example = format!("cool! {}", shadowing_example);
693 /// shadowing_example += " something else!"; // not shadowing
696 /// Other places the `let` keyword is used include along with [`if`], in the form of `if let`
697 /// expressions. They're useful if the pattern being matched isn't exhaustive, such as with
698 /// enumerations. `while let` also exists, which runs a loop with a pattern matched value until
699 /// that pattern can't be matched.
701 /// For more information on the `let` keyword, see the [Rust book][book2] or the [Reference]
703 /// [book1]: ../book/ch06-02-match.html
704 /// [`if`]: keyword.if.html
705 /// [book2]: ../book/ch18-01-all-the-places-for-patterns.html#let-statements
706 /// [Reference]: ../reference/statements.html#let-statements
709 #[doc(keyword = "while")]
711 /// Loop while a condition is upheld.
713 /// A `while` expression is used for predicate loops. The `while` expression runs the conditional
714 /// expression before running the loop body, then runs the loop body if the conditional
715 /// expression evaluates to `true`, or exits the loop otherwise.
718 /// let mut counter = 0;
720 /// while counter < 10 {
721 /// println!("{}", counter);
726 /// Like the [`for`] expression, we can use `break` and `continue`. A `while` expression
727 /// cannot break with a value and always evaluates to `()` unlike [`loop`].
735 /// break; // Exit when `i` is 64.
740 /// As `if` expressions have their pattern matching variant in `if let`, so too do `while`
741 /// expressions with `while let`. The `while let` expression matches the pattern against the
742 /// expression, then runs the loop body if pattern matching succeeds, or exits the loop otherwise.
743 /// We can use `break` and `continue` in `while let` expressions just like in `while`.
746 /// let mut counter = Some(0);
748 /// while let Some(i) = counter {
752 /// println!("{}", i);
753 /// counter = Some (i + 1);
758 /// For more information on `while` and loops in general, see the [reference].
760 /// [`for`]: keyword.for.html
761 /// [`loop`]: keyword.loop.html
762 /// [reference]: ../reference/expressions/loop-expr.html#predicate-loops
763 mod while_keyword { }
765 #[doc(keyword = "loop")]
767 /// Loop indefinitely.
769 /// `loop` is used to define the simplest kind of loop supported in Rust. It runs the code inside
770 /// it until the code uses `break` or the program exits.
774 /// println!("hello world forever!");
780 /// println!("i is {}", i);
786 /// assert_eq!(i, 128);
789 /// Unlike the other kinds of loops in Rust (`while`, `while let`, and `for`), loops can be used as
790 /// expressions that return values via `break`.
794 /// let something = loop {
800 /// assert_eq!(something, 128);
803 /// Every `break` in a loop has to have the same type. When it's not explicitly giving something,
804 /// `break;` returns `()`.
806 /// For more information on `loop` and loops in general, see the [Reference].
808 /// [Reference]: ../reference/expressions/loop-expr.html
811 #[doc(keyword = "match")]
813 /// Control flow based on pattern matching.
815 /// `match` can be used to run code conditionally. Every pattern must
816 /// be handled exhaustively either explicitly or by using wildcards like
817 /// `_` in the `match`. Since `match` is an expression, values can also be
821 /// let opt = Option::None::<usize>;
822 /// let x = match opt {
823 /// Some(int) => int,
826 /// assert_eq!(x, 10);
828 /// let a_number = Option::Some(10);
830 /// Some(x) if x <= 5 => println!("0 to 5 num = {}", x),
831 /// Some(x @ 6..=10) => println!("6 to 10 num = {}", x),
832 /// None => panic!(),
833 /// // all other numbers
838 /// `match` can be used to gain access to the inner members of an enum
839 /// and use them directly.
843 /// Double(Option<u8>, Option<String>),
844 /// Single(Option<u8>),
848 /// let get_inner = Outer::Double(None, Some(String::new()));
849 /// match get_inner {
850 /// Outer::Double(None, Some(st)) => println!("{}", st),
851 /// Outer::Single(opt) => println!("{:?}", opt),
856 /// For more information on `match` and matching in general, see the [Reference].
858 /// [Reference]: ../reference/expressions/match-expr.html
859 mod match_keyword { }
861 #[doc(keyword = "mod")]
863 /// Organize code into [modules].
865 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
867 /// [modules]: ../reference/items/modules.html
868 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
871 #[doc(keyword = "move")]
873 /// Capture a [closure]'s environment by value.
875 /// `move` converts any variables captured by reference or mutable reference
876 /// to owned by value variables. The three [`Fn` trait]'s mirror the ways to capture
877 /// variables, when `move` is used, the closures is represented by the `FnOnce` trait.
880 /// let capture = "hello";
881 /// let closure = move || {
882 /// println!("rust says {}", capture);
886 /// `move` is often used when [threads] are involved.
891 /// std::thread::spawn(move || {
892 /// println!("captured {} by value", x)
893 /// }).join().unwrap();
895 /// // x is no longer available
898 /// For more information on the `move` keyword, see the [closure]'s section
899 /// of the Rust book or the [threads] section
901 /// [`Fn` trait]: ../std/ops/trait.Fn.html
902 /// [closure]: ../book/ch13-01-closures.html
903 /// [threads]: ../book/ch16-01-threads.html#using-move-closures-with-threads
906 #[doc(keyword = "mut")]
908 /// A mutable binding, reference, or pointer.
910 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
912 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
915 #[doc(keyword = "pub")]
917 /// Make an item visible to others.
919 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
921 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
924 #[doc(keyword = "ref")]
926 /// Bind by reference during pattern matching.
928 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
930 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
933 #[doc(keyword = "return")]
935 /// Return a value from a function.
937 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
939 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
940 mod return_keyword { }
942 #[doc(keyword = "self")]
944 /// The receiver of a method, or the current module.
946 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
948 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
951 #[doc(keyword = "Self")]
953 /// The implementing type within a [`trait`] or [`impl`] block, or the current type within a type
956 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
958 /// [`impl`]: keyword.impl.html
959 /// [`trait`]: keyword.trait.html
960 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
961 mod self_upper_keyword { }
963 #[doc(keyword = "static")]
965 /// A place that is valid for the duration of a program.
967 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
969 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
970 mod static_keyword { }
972 #[doc(keyword = "struct")]
974 /// A type that is composed of other types.
976 /// Structs in Rust come in three flavors: Structs with named fields, tuple structs, and unit
986 /// struct Tuple(u32, String);
991 /// Regular structs are the most commonly used. Each field defined within them has a name and a
992 /// type, and once defined can be accessed using `example_struct.field` syntax. The fields of a
993 /// struct share its mutability, so `foo.bar = 2;` would only be valid if `foo` was mutable. Adding
994 /// `pub` to a field makes it visible to code in other modules, as well as allowing it to be
995 /// directly accessed and modified.
997 /// Tuple structs are similar to regular structs, but its fields have no names. They are used like
998 /// tuples, with deconstruction possible via `let TupleStruct(x, y) = foo;` syntax. For accessing
999 /// individual variables, the same syntax is used as with regular tuples, namely `foo.0`, `foo.1`,
1000 /// etc, starting at zero.
1002 /// Unit structs are most commonly used as marker. They have a size of zero bytes, but unlike empty
1003 /// enums they can be instantiated, making them isomorphic to the unit type `()`. Unit structs are
1004 /// useful when you need to implement a trait on something, but don't need to store any data inside
1009 /// Structs can be instantiated in different ways, all of which can be mixed and
1010 /// matched as needed. The most common way to make a new struct is via a constructor method such as
1011 /// `new()`, but when that isn't available (or you're writing the constructor itself), struct
1012 /// literal syntax is used:
1015 /// # struct Foo { field1: f32, field2: String, etc: bool }
1016 /// let example = Foo {
1018 /// field2: "blah".to_string(),
1023 /// It's only possible to directly instantiate a struct using struct literal syntax when all of its
1024 /// fields are visible to you.
1026 /// There are a handful of shortcuts provided to make writing constructors more convenient, most
1027 /// common of which is the Field Init shorthand. When there is a variable and a field of the same
1028 /// name, the assignment can be simplified from `field: field` into simply `field`. The following
1029 /// example of a hypothetical constructor demonstrates this:
1038 /// pub fn new(name: String) -> Self {
1047 /// Another shortcut for struct instantiation is available, used when you need to make a new
1048 /// struct that has the same values as most of a previous struct of the same type, called struct
1052 /// # struct Foo { field1: String, field2: () }
1053 /// # let thing = Foo { field1: "".to_string(), field2: () };
1054 /// let updated_thing = Foo {
1055 /// field1: "a new value".to_string(),
1060 /// Tuple structs are instantiated in the same way as tuples themselves, except with the struct's
1061 /// name as a prefix: `Foo(123, false, 0.1)`.
1063 /// Empty structs are instantiated with just their name, and don't need anything else. `let thing =
1066 /// # Style conventions
1068 /// Structs are always written in CamelCase, with few exceptions. While the trailing comma on a
1069 /// struct's list of fields can be omitted, it's usually kept for convenience in adding and
1070 /// removing fields down the line.
1072 /// For more information on structs, take a look at the [Rust Book][book] or the
1073 /// [Reference][reference].
1075 /// [`PhantomData`]: marker/struct.PhantomData.html
1076 /// [book]: ../book/ch05-01-defining-structs.html
1077 /// [reference]: ../reference/items/structs.html
1078 mod struct_keyword { }
1080 #[doc(keyword = "super")]
1082 /// The parent of the current [module].
1084 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1086 /// [module]: ../reference/items/modules.html
1087 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1088 mod super_keyword { }
1090 #[doc(keyword = "trait")]
1092 /// A common interface for a class of types.
1094 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1096 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1097 mod trait_keyword { }
1099 #[doc(keyword = "true")]
1101 /// A value of type [`bool`] representing logical **true**.
1103 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1105 /// [`bool`]: primitive.bool.html
1106 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1107 mod true_keyword { }
1109 #[doc(keyword = "type")]
1111 /// Define an alias for an existing type.
1113 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1115 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1116 mod type_keyword { }
1118 #[doc(keyword = "unsafe")]
1120 /// Code or interfaces whose [memory safety] cannot be verified by the type system.
1122 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1124 /// [memory safety]: ../book/ch19-01-unsafe-rust.html
1125 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1126 mod unsafe_keyword { }
1128 #[doc(keyword = "use")]
1130 /// Import or rename items from other crates or modules.
1132 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1134 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1137 #[doc(keyword = "where")]
1139 /// Add constraints that must be upheld to use an item.
1141 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1143 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1144 mod where_keyword { }
1146 // 2018 Edition keywords
1148 #[doc(keyword = "async")]
1150 /// Return a [`Future`] instead of blocking the current thread.
1152 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1154 /// [`Future`]: ./future/trait.Future.html
1155 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1156 mod async_keyword { }
1158 #[doc(keyword = "await")]
1160 /// Suspend execution until the result of a [`Future`] is ready.
1162 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1164 /// [`Future`]: ./future/trait.Future.html
1165 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1166 mod await_keyword { }
1168 #[doc(keyword = "dyn")]
1170 /// Name the type of a [trait object].
1172 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1174 /// [trait object]: ../book/ch17-02-trait-objects.html
1175 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1178 #[doc(keyword = "union")]
1180 /// The [Rust equivalent of a C-style union][union].
1182 /// The documentation for this keyword is [not yet complete]. Pull requests welcome!
1184 /// [union]: ../reference/items/unions.html
1185 /// [not yet complete]: https://github.com/rust-lang/rust/issues/34601
1186 mod union_keyword { }