204 lines
6.1 KiB
Markdown
204 lines
6.1 KiB
Markdown
% Rust Cheatsheet
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# How do I convert *X* to *Y*?
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**Int to string**
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Use [`ToStr`](http://static.rust-lang.org/doc/master/std/to_str/trait.ToStr.html).
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```rust
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let x: int = 42;
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let y: ~str = x.to_str();
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```
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**String to int**
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Use [`FromStr`](http://static.rust-lang.org/doc/master/std/from_str/trait.FromStr.html), and its helper function, [`from_str`](http://static.rust-lang.org/doc/master/std/from_str/fn.from_str.html).
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```rust
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let x: Option<int> = from_str("42");
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let y: int = x.unwrap();
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```
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**Int to string, in non-base-10**
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Use [`ToStrRadix`](http://static.rust-lang.org/doc/master/std/num/trait.ToStrRadix.html).
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```rust
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use std::num::ToStrRadix;
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let x: int = 42;
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let y: ~str = x.to_str_radix(16);
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```
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**String to int, in non-base-10**
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Use [`FromStrRadix`](http://static.rust-lang.org/doc/master/std/num/trait.FromStrRadix.html), and its helper function, [`from_str_radix`](http://static.rust-lang.org/doc/master/std/num/fn.from_str_radix.html).
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```rust
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use std::num::from_str_radix;
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let x: Option<int> = from_str_radix("deadbeef", 16);
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let y: int = x.unwrap();
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```
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# File operations
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## How do I read from a file?
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Use [`File::open`](http://static.rust-lang.org/doc/master/std/io/fs/struct.File.html#method.open) to create a [`File`](http://static.rust-lang.org/doc/master/std/io/fs/struct.File.html) struct, which implements the [`Reader`](http://static.rust-lang.org/doc/master/std/io/trait.Reader.html) trait.
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```rust
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use std::path::Path;
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use std::io::fs::File;
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let path : Path = Path::new("Doc-FAQ-Cheatsheet.md");
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let on_error = || fail!("open of {:?} failed", path);
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let reader : File = File::open(&path).unwrap_or_else(on_error);
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```
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## How do I iterate over the lines in a file?
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Use the [`lines`](http://static.rust-lang.org/doc/master/std/io/trait.Buffer.html#method.lines) method on a [`BufferedReader`](http://static.rust-lang.org/doc/master/std/io/buffered/struct.BufferedReader.html).
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```rust
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use std::io::buffered::BufferedReader;
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let mut reader = BufferedReader::new(reader);
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for line in reader.lines() {
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print!("line: {}", line);
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}
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```
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# String operations
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## How do I search for a substring?
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Use the [`find_str`](http://static.rust-lang.org/doc/master/std/str/trait.StrSlice.html#tymethod.find_str) method.
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```rust
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let str = "Hello, this is some random string";
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let index: Option<uint> = str.find_str("rand");
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```
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# Containers
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## How do I get the length of a vector?
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The [`Container`](http://static.rust-lang.org/doc/master/std/container/trait.Container.html) trait provides the `len` method.
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```rust
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let u: ~[u32] = ~[0, 1, 2];
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let v: &[u32] = &[0, 1, 2, 3];
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let w: [u32, .. 5] = [0, 1, 2, 3, 4];
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println!("u: {}, v: {}, w: {}", u.len(), v.len(), w.len()); // 3, 4, 5
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```
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## How do I iterate over a vector?
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Use the [`iter`](http://static.rust-lang.org/doc/master/std/vec/trait.ImmutableVector.html#tymethod.iter) method.
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```rust
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let values: ~[int] = ~[1, 2, 3, 4, 5];
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for value in values.iter() { // value: &int
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println!("{}", *value);
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}
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```
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(See also [`mut_iter`](http://static.rust-lang.org/doc/master/std/vec/trait.MutableVector.html#tymethod.mut_iter) which yields `&mut int` and [`move_iter`](http://static.rust-lang.org/doc/master/std/vec/trait.OwnedVector.html#tymethod.move_iter) which yields `int` while consuming the `values` vector.)
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# Type system
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## How do I store a function in a struct?
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```rust
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struct Foo {
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myfunc: fn(int, uint) -> i32
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}
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struct FooClosure<'a> {
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myfunc: 'a |int, uint| -> i32
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}
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fn a(a: int, b: uint) -> i32 {
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(a as uint + b) as i32
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}
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fn main() {
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let f = Foo { myfunc: a };
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let g = FooClosure { myfunc: |a, b| { (a - b as int) as i32 } };
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println!("{}", (f.myfunc)(1, 2));
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println!("{}", (g.myfunc)(3, 4));
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}
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```
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Note that the parenthesis surrounding `f.myfunc` are necessary: they are how Rust disambiguates field lookup and method call. The `'a` on `FooClosure` is the lifetime of the closure's environment pointer.
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## How do I express phantom types?
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[Phantom types](http://www.haskell.org/haskellwiki/Phantom_type) are those that cannot be constructed at compile time. To express these in Rust, zero-variant `enum`s can be used:
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```rust
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enum Open {}
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enum Closed {}
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```
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Phantom types are useful for enforcing state at compile time. For example:
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```rust
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struct Door<State>(~str);
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fn close(Door(name): Door<Open>) -> Door<Closed> {
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Door::<Closed>(name)
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}
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fn open(Door(name): Door<Closed>) -> Door<Open> {
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Door::<Open>(name)
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}
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let _ = close(Door::<Open>(~"front")); // ok
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let _ = close(Door::<Closed>(~"front")); // error: mismatched types: expected `main::Door<main::Open>` but found `main::Door<main::Closed>`
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```
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# FFI (Foreign Function Interface)
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## C function signature conversions
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Description | C signature | Equivalent Rust signature
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----------------------|----------------------------------------------|------------------------------------------
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no parameters | `void foo(void);` | `fn foo();`
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return value | `int foo(void);` | `fn foo() -> c_int;`
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function parameters | `void foo(int x, int y);` | `fn foo(x: int, y: int);`
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in-out pointers | `void foo(const int* in_ptr, int* out_ptr);` | `fn foo(in_ptr: *c_int, out_ptr: *mut c_int);`
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Note: The Rust signatures should be wrapped in an `extern "ABI" { ... }` block.
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### Representing opaque handles
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You might see things like this in C APIs:
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```c
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typedef struct Window Window;
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Window* createWindow(int width, int height);
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```
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You can use a zero-element `enum` ([phantom type](#how-do-i-express-phantom-types)) to represent the opaque object handle. The FFI would look like this:
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```rust
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enum Window {}
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extern "C" {
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fn createWindow(width: c_int, height: c_int) -> *Window;
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}
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```
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Using a phantom type ensures that the handles cannot be (safely) constructed in client code.
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# Contributing to this page
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For small examples, have full type annotations, as much as is reasonable, to keep it clear what, exactly, everything is doing. Try to link to the API docs, as well.
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Similar documents for other programming languages:
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* [http://pleac.sourceforge.net/](http://pleac.sourceforge.net)
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