Method permute_fn

src/expr/src/linear.rs:899–926

Update input column references, due to an input projection or permutation. The `shuffle` argument remaps expected column identifiers to new locations, with the expectation that `shuffle` describes all input columns, and so the intermediate results will be able to start at position `shuffle.len()`. The supplied `shuffle` might not list columns that are not "demanded" by the instance, and so we sh

(&mut self, remap: F, new_input_arity: usize)

    /// instance, and so we should ensure that `self` is optimized to not reference
    /// columns that are not demanded.
    pub fn permute_fn<F>(&mut self, remap: F, new_input_arity: usize)
    where
        F: Fn(usize) -> usize,
    {
        let (mut map, mut filter, mut project) = self.as_map_filter_project();
        let map_len = map.len();
        let action = |col: &mut usize| {
            if self.input_arity <= *col && *col < self.input_arity + map_len {
                *col = new_input_arity + (*col - self.input_arity);
            } else {
                *col = remap(*col);
            }
        };
        for expr in map.iter_mut() {
            expr.visit_columns(action);
        }
        for pred in filter.iter_mut() {
            pred.visit_columns(action);
        }
        for proj in project.iter_mut() {
            action(proj);
            assert!(*proj < new_input_arity + map.len());
        }
        *self = Self::new(new_input_arity)
            .map(map)
            .filter(filter)
            .project(project)
    }
}

// Optimization routines.