"Multiple traits" approach for clap_derive

sketch.rs

/// This trait is just a convenience on top of FromArgMatches + IntoApp
///
/// All the methods are provided.
trait Clap: FromArgMatches + IntoApp + Sized {
    /// Parse from `std::env::args()`, exit on error
    fn parse() -> Self {
        let matches = <Self as IntoApp>::into_app().get_matches();
        <Self as FromArgMatches>::from_argmatches(matches)
    }
    
    /// Parse from `std::env::args()`, return Err on error.
    fn try_parse() -> Result<Self, ClapErr> {
        let matches = <Self as IntoApp>::into_app().try_get_matches()?;
        Ok(<Self as FromArgMatches>::from_argmatches(matches))
    }
    
    /// Parse from iterator, exit on error
    pub fn parse_from<I, T>(itr: I) -> #name
    where
        I: IntoIterator<Item = T>,
        T: Into<OsString> + Clone 
    {
        let matches = <Self as IntoApp>::into_app().get_matches_from(itr);
        <Self as FromArgMatches>::from_argmatches(matches)
    }
    
    /// Parse from `std::env::args()`, return Err on error.
    fn try_parse_from(itr: I) -> Result<Self, ClapErr> 
    where
        I: IntoIterator<Item = T>,
        T: Into<OsString> + Clone 
    {
        let matches = <Self as IntoApp>::into_app().try_get_matches_from(itr)?;
        Ok(<Self as FromArgMatches>::from_argmatches(matches))
    }
}

/// Build an App according to the struct
///
/// Also serves fro flatening 
trait IntoApp: Sized {
    fn into_app<'b>() -> clap::App<'b>;
    fn augment_clap<'b>(app: clap::App<'b>) -> App<'b>;
}

/// Extract values from ArgMatches into the struct.
trait FromArgMatches: Sized {
    fn from_argmatches<'b>(app: clap::App<'b>) -> Self;
}

trait Subcommand {
    fn from_subcommand<'b>(name: &str, matches: ArgMatches) -> Option<Self>;
}