"Conditional compilation" blocks

[bonsairobo]

Sometimes you get into tricky situations where you just need to specialize the archived implementation of a method. We might be able to support something like:

#[archive_impl]
impl Foo {
    fn do_it_up(&self) {
        #[if_archived] {
            // some archived-specific logic, like deserializing
        } #[else] {
            // the alternative
        }
    }
}

I don't know if that's good syntax. We might need to experiment.

[bonsairobo]

The alternative is to just add a method with the same name to both Foo and ArchivedFoo. This probably works better most of the time.