如何实现阅读特质?[副本]

error[E0277]: the trait bound `Result<File, std::io::Error>: std::io::Read` is not satisfied
    --> src/main.rs:77:39
     |
77   |     let yaml = serde_yml::from_reader(f)?;
     |                ---------------------- ^ the trait `std::io::Read` is not implemented for `Result<File, std::io::Error>`
     |                |
     |                required by a bound introduced by this call
     |
note: required by a bound in `from_reader`
    --> /home/pepp/.cargo/registry/src/index.crates.io-1949cf2c6b52557f/serde_yml-0.0.12/src/de.rs:2326:8
     |
2324 | pub fn from_reader<R, T>(rdr: R) -> Result<T>
     |        ----------- required by a bound in this function
2325 | where
2326 |     R: io::Read,
     |        ^^^^^^^^ required by this bound in `from_reader`

For more information about this error, try `rustc --explain E0277`.

fn parse_yml(conf: PathBuf) -> Result<(), Box<dyn std::error::Error>> {

    println!("conf: {:?}", conf);

    let f = File::open(conf);

    let yaml = serde_yml::from_reader(f)?;

    println!("yaml: {}", yaml);

    Ok(())
}

我的理解是File已经包含了read trait,所以当我阅读E0277时,我对在它已经拥有的东西上实现trait感到困惑。E0277似乎是关于实现用户定义的特性。