1# downcast   ![Latest Version]
2
3[Latest Version]: https://img.shields.io/crates/v/downcast.svg
4
5A trait (& utilities) for downcasting trait objects back to their original types.
6
7## [link to API documentation](https://docs.rs/downcast)
8
9## example usage
10
11Add to your Cargo.toml:
12
13```toml
14[dependencies]
15downcast = "0.12"
16```
17
18Add to your crate root:
19
20```rust
21#[macro_use]
22extern crate downcast;
23```
24
25* [simple](examples/simple.rs) showcases the most simple usage of this library.
26* [with_params](examples/with_params.rs)  showcases how to deal with traits who have type parameters.
27* [sync_service](examples/sync_service.rs)  showcases how to downcast `Arc`-pointers.
28
29## build features
30
31* **std (default)** enables all functionality requiring the standard library (`Downcast::downcast()`).
32* **nightly** enables all functionality requiring rust nightly (`Any::type_name()`).
33
34## faq
35
36__Q: I'm getting `the size for values of type XXX cannot be known at compile time` errors, what am i doing wrong?__
37
38A: Make sure you use the corresponding `Any` bound along with the `Downcast` traits. So, `Any` for `Downcast` and `AnySync` for `DowncastSync`.
39
40__Q: Can i cast trait objects to trait objects?__
41
42A: No, that is currently no possible in safe rust - and unsafe solutions are very tricky, as well. If you found a solution, feel free to share it!
43
44__Q: What is the difference between this and the `downcast-rs` crate on crates.io?__
45
46A: At the moment, there isn't one, really.
47There was an unfortunate naming clash. You may consider using the other crate, as it is more actively maintained.
48This one is considered feature-complete and frozen in functionality.
49Hopefully, one day, the Rust language will make downcasting easier and we will need neither of these crates anymore!
50