# auto_enums
[](https://travis-ci.org/taiki-e/auto_enums)
[](https://crates.io/crates/auto_enums/)
[](https://docs.rs/auto_enums/)
[](https://crates.io/crates/auto_enums/)
[](https://blog.rust-lang.org/2018/10/25/Rust-1.30.0.html)
A library for to allow multiple return types by automatically generated enum.
This library provides the following attribute macros:
* `#[auto_enum]`
Parses syntax, creates the enum, inserts variants, and passes specified traits to `#[enum_derive]`.
* `#[enum_derive]`
Implements specified traits to the enum.
## Usage
Add this to your `Cargo.toml`:
```toml
[dependencies]
auto_enums = "0.3"
```
and this to your crate root:
```rust
#[macro_use]
extern crate auto_enums;
```
## Examples
`#[auto_enum]`'s basic feature is to wrap the value returned by the last if or match expression by an enum that implemented the specified traits.
```rust
#[auto_enum(Iterator)]
fn foo(x: i32) -> impl Iterator<Item = i32> {
match x {
0 => 1..10,
_ => vec![5, 10].into_iter(),
}
}
```
`#[auto_enum]` generates code in two stages.
First, `#[auto_enum]` will do the following.
* parses syntax
* creates the enum
* inserts variants
Code like this will be generated:
```rust
fn foo(x: i32) -> impl Iterator<Item = i32> {
#[enum_derive(Iterator)]
enum __Enum1<__T1, __T2> {
__T1(__T1),
__T2(__T2),
}
match x {
0 => __Enum1::__T1(1..10),
_ => __Enum1::__T2(vec![5, 10].into_iter()),
}
}
```
Next, `#[enum_derive]` implements the specified traits.
[Code like this will be generated](docs/example-1.md)
See [API Documentation](https://docs.rs/auto_enums/) for more details.
## Supported traits
`#[enum_derive]` implements the supported traits and passes unsupported traits to `#[derive]`.
If you want to use traits that are not supported by `#[enum_derive]`, you can use another crate that provides `proc_macro_derive`, or you can define `proc_macro_derive` yourself ([derive_utils] probably can help it).
Basic usage of `#[enum_derive]`
```rust
// `#[enum_derive]` implements `Iterator`, and `#[derive]` implements `Clone`.
#[enum_derive(Iterator, Clone)]
enum Foo<A, B> {
A(A),
B(B),
}
```
[derive_utils]: https://crates.io/crates/derive_utils
### [std|core] libraries
Note that some traits have aliases.
`[std|core]::ops`
* [`Deref`](https://doc.rust-lang.org/std/ops/trait.Deref.html)
* [`DerefMut`](https://doc.rust-lang.org/std/ops/trait.DerefMut.html)
* [`Index`](https://doc.rust-lang.org/std/ops/trait.Index.html)
* [`IndexMut`](https://doc.rust-lang.org/std/ops/trait.IndexMut.html)
* [`Fn`](https://doc.rust-lang.org/std/ops/trait.Fn.html) (*nightly-only*)
* [`FnMut`](https://doc.rust-lang.org/std/ops/trait.FnMut.html) (*nightly-only*)
* [`FnOnce`](https://doc.rust-lang.org/std/ops/trait.FnOnce.html) (*nightly-only*)
* [`RangeBounds`](https://doc.rust-lang.org/std/ops/trait.RangeBounds.html)
`[std|core]::convert`
* [`AsRef`](https://doc.rust-lang.org/std/convert/trait.AsRef.html)
* [`AsMut`](https://doc.rust-lang.org/std/convert/trait.AsMut.html)
`[std|core]::iter`
* [`Iterator`](https://doc.rust-lang.org/std/iter/trait.Iterator.html)
* [`DoubleEndedIterator`](https://doc.rust-lang.org/std/iter/trait.DoubleEndedIterator.html)
* [`ExactSizeIterator`](https://doc.rust-lang.org/std/iter/trait.ExactSizeIterator.html)
* [`FusedIterator`](https://doc.rust-lang.org/std/iter/trait.FusedIterator.html)
* [`TrustedLen`](https://doc.rust-lang.org/std/iter/trait.TrustedLen.html) (*nightly-only*)
* [`Extend`](https://doc.rust-lang.org/std/iter/trait.Extend.html)
`[std|core]::fmt`
* [`Debug`](https://doc.rust-lang.org/std/fmt/trait.Debug.html) (alias: `fmt::Debug`) - [generated code](docs/supported_traits/std/debug.md)
* [`Display`](https://doc.rust-lang.org/std/fmt/trait.Display.html) (alias: `fmt::Display`)
* [`fmt::Binary`](https://doc.rust-lang.org/std/fmt/trait.Binary.html) (*requires `"fmt"` crate feature*)
* [`fmt::LowerExp`](https://doc.rust-lang.org/std/fmt/trait.LowerExp.html) (*requires `"fmt"` crate feature*)
* [`fmt::LowerHex`](https://doc.rust-lang.org/std/fmt/trait.LowerHex.html) (*requires `"fmt"` crate feature*)
* [`fmt::Octal`](https://doc.rust-lang.org/std/fmt/trait.Octal.html) (*requires `"fmt"` crate feature*)
* [`fmt::Pointer`](https://doc.rust-lang.org/std/fmt/trait.Pointer.html) (*requires `"fmt"` crate feature*)
* [`fmt::UpperExp`](https://doc.rust-lang.org/std/fmt/trait.UpperExp.html) (*requires `"fmt"` crate feature*)
* [`fmt::UpperHex`](https://doc.rust-lang.org/std/fmt/trait.UpperHex.html) (*requires `"fmt"` crate feature*)
* [`fmt::Write`](https://doc.rust-lang.org/std/fmt/trait.Write.html)
`[std|core]::future`
* [`Future`](https://doc.rust-lang.org/std/future/trait.Future.html) - *nightly-only*
`std::io`
* [`Read`](https://doc.rust-lang.org/std/io/trait.Read.html) (alias: `io::Read`)
* [`BufRead`](https://doc.rust-lang.org/std/io/trait.BufRead.html) (alias: `io::BufRead`)
* [`Write`](https://doc.rust-lang.org/std/io/trait.Write.html) (alias: `io::Write`)
* [`Seek`](https://doc.rust-lang.org/std/io/trait.Seek.html) (alias: `io::Seek`)
`std::error`
* [`Error`](https://doc.rust-lang.org/std/error/trait.Error.html) - [generated code](docs/supported_traits/std/error.md)
### External libraries
You can add support for external library by activating the each crate feature.
[`futures(v0.3)`](https://github.com/rust-lang-nursery/futures-rs) (*requires `"futures"` crate feature*)
* [`futures::Stream`](https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.11/futures/stream/trait.Stream.html)
* [`futures::Sink`](https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.11/futures/sink/trait.Sink.html)
* [`futures::AsyncRead`](https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.11/futures/io/trait.AsyncRead.html)
* [`futures::AsyncWrite`](https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.11/futures/io/trait.AsyncWrite.html)
[`futures(v0.1)`](https://github.com/rust-lang-nursery/futures-rs) (*requires `"futures01"` crate feature*)
* [`futures01::Future`](https://docs.rs/futures/0.1/futures/future/trait.Future.html)
* [`futures01::Stream`](https://docs.rs/futures/0.1/futures/stream/trait.Stream.html)
* [`futures01::Sink`](https://docs.rs/futures/0.1/futures/sink/trait.Sink.html)
[`quote`](https://github.com/dtolnay/quote) (*requires `"proc_macro"` crate feature*)
* [`quote::ToTokens`](https://docs.rs/quote/0.6/quote/trait.ToTokens.html)
[`rayon`](https://github.com/rayon-rs/rayon) (*requires `"rayon"` crate feature*)
* [`rayon::ParallelIterator`](https://docs.rs/rayon/1.0/rayon/iter/trait.ParallelIterator.html)
* [`rayon::IndexedParallelIterator`](https://docs.rs/rayon/1.0/rayon/iter/trait.IndexedParallelIterator.html)
* [`rayon::ParallelExtend`](https://docs.rs/rayon/1.0/rayon/iter/trait.ParallelExtend.html)
[`serde`](https://github.com/serde-rs/serde) (*requires `"serde"` crate feature*)
* [`serde::Serialize`](https://docs.serde.rs/serde/trait.Serialize.html) - [generated code](docs/supported_traits/external/serde/serialize.md)
## Rust Version
The current minimum required Rust version is 1.30.
## License
Licensed under either of
* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or <http://www.apache.org/licenses/LICENSE-2.0>)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or <http://opensource.org/licenses/MIT>)
at your option.
### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.