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{{#title rust::Slice<T> — Rust ♡ C++}}
# rust::Slice\<const T\>, rust::Slice\<T\>
- Rust `&[T]` is written `rust::Slice<const T>` in C++
- Rust `&mut [T]` is written `rust::Slice<T>` in C++
### Public API:
```cpp,hidelines=...
// rust/cxx.h
...
...#include <iterator>
...#include <type_traits>
...
...namespace rust {
template <typename T>
class Slice final {
public:
using value_type = T;
Slice() noexcept;
Slice(const Slice<T> &) noexcept;
Slice(T *, size_t count) noexcept;
Slice &operator=(Slice<T> &&) noexcept;
Slice &operator=(const Slice<T> &) noexcept
requires std::is_const_v<T>;
T *data() const noexcept;
size_t size() const noexcept;
size_t length() const noexcept;
bool empty() const noexcept;
T &operator[](size_t n) const noexcept;
T &at(size_t n) const;
T &front() const noexcept;
T &back() const noexcept;
class iterator;
iterator begin() const noexcept;
iterator end() const noexcept;
void swap(Slice &) noexcept;
};
...
...template <typename T>
...class Slice<T>::iterator final {
...public:
... using iterator_category = std::random_access_iterator_tag;
... using value_type = T;
... using pointer = T *;
... using reference = T &;
...
... T &operator*() const noexcept;
... T *operator->() const noexcept;
... T &operator[](ptrdiff_t) const noexcept;
...
... iterator &operator++() noexcept;
... iterator operator++(int) noexcept;
... iterator &operator--() noexcept;
... iterator operator--(int) noexcept;
...
... iterator &operator+=(ptrdiff_t) noexcept;
... iterator &operator-=(ptrdiff_t) noexcept;
... iterator operator+(ptrdiff_t) const noexcept;
... iterator operator-(ptrdiff_t) const noexcept;
... ptrdiff_t operator-(const iterator &) const noexcept;
...
... bool operator==(const iterator &) const noexcept;
... bool operator!=(const iterator &) const noexcept;
... bool operator<(const iterator &) const noexcept;
... bool operator>(const iterator &) const noexcept;
... bool operator<=(const iterator &) const noexcept;
... bool operator>=(const iterator &) const noexcept;
...};
...
...} // namespace rust
```
### Restrictions:
T must not be an opaque Rust type or opaque C++ type. Support for opaque Rust
types in slices is coming.
Allowed as function argument or return value. Not supported in shared structs.
Only rust::Slice\<const T\> is copy-assignable, not rust::Slice\<T\>. (Both are
move-assignable.) You'll need to write std::move occasionally as a reminder that
accidentally exposing overlapping &mut \[T\] to Rust is UB.
## Example
This example is a C++ program that constructs a slice containing JSON data (by
reading from stdin, but it could be from anywhere), then calls into Rust to
pretty-print that JSON data into a std::string via the [serde_json] and
[serde_transcode] crates.
[serde_json]: https://github.com/serde-rs/json
[serde_transcode]: https://github.com/sfackler/serde-transcode
```rust,noplayground
// src/main.rs
#![no_main] // main defined in C++ by main.cc
use cxx::CxxString;
use std::io::{self, Write};
use std::pin::Pin;
#[cxx::bridge]
mod ffi {
extern "Rust" {
fn prettify_json(input: &[u8], output: Pin<&mut CxxString>) -> Result<()>;
}
}
struct WriteToCxxString<'a>(Pin<&'a mut CxxString>);
impl<'a> Write for WriteToCxxString<'a> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
self.0.as_mut().push_bytes(buf);
Ok(buf.len())
}
fn flush(&mut self) -> io::Result<()> {
Ok(())
}
}
fn prettify_json(input: &[u8], output: Pin<&mut CxxString>) -> serde_json::Result<()> {
let writer = WriteToCxxString(output);
let mut deserializer = serde_json::Deserializer::from_slice(input);
let mut serializer = serde_json::Serializer::pretty(writer);
serde_transcode::transcode(&mut deserializer, &mut serializer)
}
```
```cpp
// src/main.cc
#include "example/src/main.rs.h"
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
int main() {
// Read json from stdin.
std::istreambuf_iterator<char> begin{std::cin}, end;
std::vector<unsigned char> input{begin, end};
rust::Slice<const uint8_t> slice{input.data(), input.size()};
// Prettify using serde_json and serde_transcode.
std::string output;
prettify_json(slice, output);
// Write to stdout.
std::cout << output << std::endl;
}
```
Testing the example:
```console
$ echo '{"fearless":"concurrency"}' | cargo run
Finished dev [unoptimized + debuginfo] target(s) in 0.02s
Running `target/debug/example`
{
"fearless": "concurrency"
}
```
|
