Crate impl_enum

Macros that make it more convenient to work with enums with variants that all implement the same trait(s).

with_methods allows you to easily delegate method calls to enum variants:

//! The variant of the writer is dynamically selected with an environment variable.
//! Using the macro, we can use the enum with the convenience of a trait object.

use std::{
    env,
    fs::File,
    io::{Cursor, Write},
};

#[impl_enum::with_methods {
    fn write_all(&mut self, buf: &[u8]) -> std::io::Result<()>
    pub fn write(&mut self, buf: &[u8]) -> std::io::Result<usize>
}]
pub enum Writer {
    Cursor(Cursor<Vec<u8>>),
    File { file: File },
}

fn get_writer() -> Writer {
    if let Ok(path) = env::var("WRITER_FILE") {
        Writer::File {
            file: File::create(path).unwrap(),
        }
    } else {
        Writer::Cursor(Cursor::new(vec![]))
    }
}

fn main() {
    let mut writer = get_writer();
    writer.write_all(b"hello!").unwrap();
}

as_dyn allows you to treat the enum as a trait object when necessary:

//! The variant of the writer is dynamically selected with an environment variable.
//! Using the macro, we can conveniently turn the enum into a trait object when necessary.

use std::{
    fmt::Debug,
    fs::File,
    io::{Cursor, Write},
};

#[impl_enum::as_dyn(Debug, Write)]
pub enum Writer {
    Cursor(Cursor<Vec<u8>>),
    File { file: File },
}

fn get_writer() -> Writer {
    if let Ok(path) = std::env::var("WRITER_FILE") {
        Writer::File {
            file: File::create(path).unwrap(),
        }
    } else {
        Writer::Cursor(Cursor::new(vec![]))
    }
}

fn main() {
    let mut writer = get_writer();

    let dyn_debug = writer.as_dyn_debug();
    println!("{:?}", dyn_debug);

    let dyn_writer_mut = writer.as_dyn_write_mut();
    dyn_writer_mut.write_all(b"hello!").unwrap();

    let box_dyn_debug = writer.into_dyn_debug();
    println!("{:?}", box_dyn_debug);
}

Attribute Macros

• as_dyn
  Generates methods for an enum that match on the enum and return the variant’s first field as a trait object.
• with_methods
  Generates methods for an enum that match on the enum and call given the method with the variant’s first field.