Attribute Macro with_methods

#[with_methods]

Generates methods for an enum that match on the enum and call given the method with the variant’s first field.

Takes a list of whitespace separated function signatures as its arguments.

Example

//! 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();
}

The macro generates an impl block equivalent to

impl Writer {
    fn write_all(&mut self, buf: &[u8]) -> std::io::Result<()> {
        match self {
            Self::Cursor(first, ..) => first.write_all(buf),
            Self::File { file, .. } => file.write_all(buf),
        }
    }
    pub fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        match self {
            Self::Cursor(first, ..) => first.write(buf),
            Self::File { file, .. } => file.write(buf),
        }
    }
}