return-type-poly.rs

use std::{
    fs::File,
    io::{BufReader, Cursor, Result},
    path::Path,
};

trait Open<T> {
    fn open(&self) -> Result<T>;
}

impl Open<File> for Path {
    fn open(&self) -> Result<File> {
        File::open(self)
    }
}

impl Open<BufReader<File>> for Path {
    fn open(&self) -> Result<BufReader<File>> {
        Ok(BufReader::new(File::open(self)?))
    }
}

impl Open<Cursor<File>> for Path {
    fn open(&self) -> Result<Cursor<File>> {
        Ok(Cursor::new(File::open(self)?))
    }
}

fn main() {
    let p = Path::new("foo");
    File::create(p).unwrap();
    dbg!(
        Open::<File>::open(p).unwrap(),
        Open::<BufReader<File>>::open(p).unwrap(),
        Open::<Cursor<File>>::open(p).unwrap(),
    );
    let _: File = dbg!(p.open().unwrap());
    let _: BufReader<File> = dbg!(p.open().unwrap());
    let _: Cursor<File> = dbg!(p.open().unwrap());
}