# rust-rc

A copy of the [http://doc.rust-lang.org/std/rc/](`std::rc`) module
that runs on stable Rust with `Weak` references.

As of this writing, `std::rc::Weak` is marked `#[unstable]`
and therefore can not be used on stable Rust yet.

To make this work, some features had to be removed:

* Unsized / dynamically-sized types `T` are not supported in `Rc<T>` or `Weak<T>`
* `#[unsafe_no_drop_flag]` is not used,
  so (in curent Rust) `Rc<T>` and `Weak<T>` have a drop flag
  and are two words big (16 bytes 64-bit platforms) instead of one.
* `NonZero` is not used,
  so `Option<Rc<T>>` and `Option<Weak<T>>` are one word bigger than `Rc<T>` or `Weak<T>`
  (for a total of 24 bytes instead of 8 on 64-bit platforms).
* `std::intrinsics::assume` is not used,
  so the optimizer may not be able to remove as many redundant checks.


## Supporting both stable and unstable Rust

This crates has an `unstable`
[Cargo feature](http://doc.crates.io/manifest.html#the-[features]-section)
that makes it simply re-export `std::rc`, so that none of the above drawbacks apply.

If you want your own code to support both stable and unstable Rust,
and get the size optimizations when available, use this crates as follows:

```toml
# Cargo.toml

[features]
unstable = ["rc/unstable"]

[dependencies]
rc = "0.1.1"
```

```rust
// lib.rs

#![cfg_attr(feature = "unstable", feature(rc_weak))]

extern crate rc;
```

```rust
// some_module.rs

use rc::{Rc, Weak};
```