step.rs

/// A step in a process.
pub trait Step<Context> {
    /// The next step in the process.
    type NextStep: Step<Context>;
    /// The error.
    type Error;

    /// A function to allow the step to progress.
    fn progress(self, context: Context) -> Result<Self::NextStep, Self::Error>;
}

/// The terminal step.
pub enum Terminal {}

impl<Context> Step<Context> for Terminal {
    type NextStep = Terminal;
    type Error = std::convert::Infallible;

    fn progress(self, _context: Context) -> Result<Self::NextStep, Self::Error> {
        // This paritcular call can never be reached since it takes self by value but that's
        // a `Terminal` which is an unconstructable type.
        unreachable!()
    }
}