auto_enums 0.2.0

A library for to allow multiple return types by automatically generated enum.
Documentation

auto_enums

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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:

[dependencies]
auto_enums = "0.2"

and this to your crate root:

#[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.

Generated code

#[auto_enum(Iterator)] // generats an enum with two variants
fn foo(x: i32) -> impl Iterator<Item = i32> {
    match x {
        0 => 1..10,
        _ => vec![5, 10].into_iter(),
    }
}

See API Documentation 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.

Basic usage of #[enum_derive]

// `#[enum_derive]` implements `Iterator`, and `#[derive]` implements `Clone`.
#[enum_derive(Iterator, Clone)]
enum Foo<A, B> {
    A(A),
    B(B),
}

[std|core] libraries

Note that some traits have aliases.

[std|core]::ops

[std|core]::convert

[std|core]::iter

[std|core]::fmt

[std|core]::future

std::io

  • Read (alias: io::Read)
  • BufRead (alias: io::BufRead)
  • Write (alias: io::Write)
  • Seek (alias: io::Seek)

std::error

External libraries

You can add support for external library by activating the each crate feature.

futures(v0.3) (requires "futures" crate feature)

futures(v0.1) (requires "futures01" crate feature)

quote (requires "proc_macro" crate feature)

rayon (requires "rayon" crate feature)

serde (requires "serde" crate feature)

  • serde::Serialize - note that it is a different implementation from #[derive(Serialize)].

Static methods

These don't derive traits, but derive static methods instead.

  • Transpose (requires "transpose_methods" crate feature) - this derives the following conversion methods.

    • transpose - convert from enum<Option<T1>,..> to Option<enum<T1,..>>

    • transpose - convert from enum<Result<T1, E1>,..> to Result<enum<T1,..>, enum<E1,..>>

    • transpose_ok - convert from enum<Result<T1, E>,..> to Option<enum<T1,..>, E>

      Examples:

      use std::{fs, io, path::Path};

#[auto_enum(Transpose, io::Write)]
fn output_stream(file: Option<&Path>) -> io::Result<impl io::Write> {
    match file {
        Some(f) => fs::File::create(f),
        None => Ok(io::stdout()),
    }.transpose_ok()
}

    • transpose_err - convert from enum<Result<T, E1>,..> to Result<T, enum<E1,..>>

Known limitations

  • There needs to explicitly specify the trait to be implemented (type_analysis crate feature reduces this limitation).

  • There needs to be marker macros for expressions other than match and if.

Rust Version

The current minimum required Rust version is 1.30.

License

Licensed under either of

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.