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48 changes: 48 additions & 0 deletions doc/complement-bugreport.md
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% HOWTO submit a RUST bug report

# I think I found a bug in the compiler!

If you see this message: ''error: internal compiler error: unexpected failure'',
then you have definitely found a bug in the compiler. It's also possible that
your code is not well-typed, but if you saw this message, it's still a bug in
error reporting.

If you see a message about an LLVM assertion failure, then you have also
definitely found a bug in the compiler. In both of these cases, it's not your
fault and you should report a bug!

If you see a compiler error message that you think is meant for users to see,
but it confuses you, *that's a bug too*. If it wasn't clear to you, then it's
an error message we want to improve, so please report it so that we can try
to make it better.

# I don't want to waste the Rust devs' time! How do I know the bug I found isn't a bug that already exists in the issue tracker?

If you don't have much time, then don't worry about that. Just submit the bug.
If it's a duplicate, somebody will notice that and close it. No one will laugh
at you, we promise (and if someone did, they would be violating the Rust
[code of conduct](https://github.com/mozilla/rust/wiki/Note-development-policy code of conduct)).

If you have more time, it's very helpful if you can type the text of the error
message you got [into the issue tracker search box](https://github.com/mozilla/rust/issues)
to see if there's an existing bug that resembles your problem. If there is,
and it's an open bug, you can comment on that issue and say you ran into it too.
This will encourage devs to fix it. But again, don't let this stop you from
submitting a bug. We'd rather have to do the work of closing duplicates than
miss out on valid bug reports.

# What information should I include in a bug report?

It's helpful to include your specific OS (for example: Mac OS X 10.8.3,
Windows 7, Ubuntu 12.0.4) and your hardware architecture (for example: i686, x86_64).
It's also helpful to copy/paste the output of re-running the erroneous rustc
commmand with the `-v` flag. Finally, if you can run the offending command under gdb,
pasting a stack trace can be useful; to do so, you will need to set a breakpoint on `rust_begin_unwind`.

# I submitted a bug, but nobody has commented on it! I'm sad.

This is sad, but does happen sometimes, since we're short-staffed. If you
submit a bug and you haven't received a comment on it within 3 business days,
it's entirely reasonable to either ask on the #rust IRC channel,
or post on the [rust-dev mailing list](https://mail.mozilla.org/listinfo/rust-dev)
to ask what the status of the bug is.
203 changes: 203 additions & 0 deletions doc/complement-cheatsheet.md
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% Rust Cheatsheet

# How do I convert *X* to *Y*?

**Int to string**

Use [`ToStr`](http://static.rust-lang.org/doc/master/std/to_str/trait.ToStr.html).

```rust
let x: int = 42;
let y: ~str = x.to_str();
```

**String to int**

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).

```rust
let x: Option<int> = from_str("42");
let y: int = x.unwrap();
```

**Int to string, in non-base-10**

Use [`ToStrRadix`](http://static.rust-lang.org/doc/master/std/num/trait.ToStrRadix.html).

```rust
use std::num::ToStrRadix;

let x: int = 42;
let y: ~str = x.to_str_radix(16);
```

**String to int, in non-base-10**

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).

```rust
use std::num::from_str_radix;

let x: Option<int> = from_str_radix("deadbeef", 16);
let y: int = x.unwrap();
```

# File operations

## How do I read from a file?

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.

```rust
use std::path::Path;
use std::io::fs::File;

let path : Path = Path::new("Doc-FAQ-Cheatsheet.md");
let on_error = || fail!("open of {:?} failed", path);
let reader : File = File::open(&path).unwrap_or_else(on_error);
```

## How do I iterate over the lines in a file?

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).

```rust
use std::io::buffered::BufferedReader;

let mut reader = BufferedReader::new(reader);
for line in reader.lines() {
print!("line: {}", line);
}
```

# String operations

## How do I search for a substring?

Use the [`find_str`](http://static.rust-lang.org/doc/master/std/str/trait.StrSlice.html#tymethod.find_str) method.

```rust
let str = "Hello, this is some random string";
let index: Option<uint> = str.find_str("rand");
```

# Containers

## How do I get the length of a vector?

The [`Container`](http://static.rust-lang.org/doc/master/std/container/trait.Container.html) trait provides the `len` method.

```rust
let u: ~[u32] = ~[0, 1, 2];
let v: &[u32] = &[0, 1, 2, 3];
let w: [u32, .. 5] = [0, 1, 2, 3, 4];

println!("u: {}, v: {}, w: {}", u.len(), v.len(), w.len()); // 3, 4, 5
```

## How do I iterate over a vector?

Use the [`iter`](http://static.rust-lang.org/doc/master/std/vec/trait.ImmutableVector.html#tymethod.iter) method.

```rust
let values: ~[int] = ~[1, 2, 3, 4, 5];
for value in values.iter() { // value: &int
println!("{}", *value);
}
```

(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.)

# Type system

## How do I store a function in a struct?

```rust
struct Foo {
myfunc: fn(int, uint) -> i32
}

struct FooClosure<'a> {
myfunc: 'a |int, uint| -> i32
}

fn a(a: int, b: uint) -> i32 {
(a as uint + b) as i32
}

fn main() {
let f = Foo { myfunc: a };
let g = FooClosure { myfunc: |a, b| { (a - b as int) as i32 } };
println!("{}", (f.myfunc)(1, 2));
println!("{}", (g.myfunc)(3, 4));
}
```

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.

## How do I express phantom types?

[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:

```rust
enum Open {}
enum Closed {}
```

Phantom types are useful for enforcing state at compile time. For example:

```rust
struct Door<State>(~str);

fn close(Door(name): Door<Open>) -> Door<Closed> {
Door::<Closed>(name)
}

fn open(Door(name): Door<Closed>) -> Door<Open> {
Door::<Open>(name)
}

let _ = close(Door::<Open>(~"front")); // ok
let _ = close(Door::<Closed>(~"front")); // error: mismatched types: expected `main::Door<main::Open>` but found `main::Door<main::Closed>`
```

# FFI (Foreign Function Interface)

## C function signature conversions

Description | C signature | Equivalent Rust signature
----------------------|----------------------------------------------|------------------------------------------
no parameters | `void foo(void);` | `fn foo();`
return value | `int foo(void);` | `fn foo() -> c_int;`
function parameters | `void foo(int x, int y);` | `fn foo(x: int, y: int);`
in-out pointers | `void foo(const int* in_ptr, int* out_ptr);` | `fn foo(in_ptr: *c_int, out_ptr: *mut c_int);`

Note: The Rust signatures should be wrapped in an `extern "ABI" { ... }` block.

### Representing opaque handles

You might see things like this in C APIs:

```c
typedef struct Window Window;
Window* createWindow(int width, int height);
```

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:

```rust
enum Window {}
extern "C" {
fn createWindow(width: c_int, height: c_int) -> *Window;
}
```

Using a phantom type ensures that the handles cannot be (safely) constructed in client code.

# Contributing to this page

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.

Similar documents for other programming languages:

* [http://pleac.sourceforge.net/](http://pleac.sourceforge.net)
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