Method implement

src/plan/union.rs:43–85

(
        &self,
        nested: &mut Iterative<'b, S, u64>,
        local_arrangements: &VariableMap<Iterative<'b, S, u64>>,
        context: &mut I,
    )

    }

    fn implement<'b, T, I, S>(
        &self,
        nested: &mut Iterative<'b, S, u64>,
        local_arrangements: &VariableMap<Iterative<'b, S, u64>>,
        context: &mut I,
    ) -> (Implemented<'b, S>, ShutdownHandle)
    where
        T: Timestamp + Lattice,
        I: ImplContext<T>,
        S: Scope<Timestamp = T>,
    {
        use differential_dataflow::AsCollection;
        use timely::dataflow::operators::Concatenate;

        let mut scope = nested.clone();
        let mut shutdown_handle = ShutdownHandle::empty();

        let streams = self.plans.iter().map(|plan| {
            let relation = {
                let (relation, shutdown) = plan.implement(&mut scope, local_arrangements, context);
                shutdown_handle.merge_with(shutdown);
                relation
            };

            let projected = {
                let (projected, shutdown) =
                    relation.projected(&mut scope, context, &self.variables);
                shutdown_handle.merge_with(shutdown);
                projected
            };

            projected.inner
        });

        let concat = nested.concatenate(streams).as_collection();

        let concatenated = CollectionRelation {
            variables: self.variables.to_vec(),
            tuples: concat.distinct(),
        };

        (Implemented::Collection(concatenated), shutdown_handle)
    }
}