Set#&

static VALUE
set_i_intersection(VALUE set, VALUE other)
{
    VALUE new_set = set_s_alloc(rb_obj_class(set));
    if (RSET_COMPARE_BY_IDENTITY(set)) {
        set_i_compare_by_identity(new_set);
    }
    set_table *stable = RSET_TABLE(set);
    set_table *ntable = RSET_TABLE(new_set);
    VALUE data;

    if (rb_obj_is_kind_of(other, rb_cSet)) {
        set_table *otable = RSET_TABLE(other);
        if (set_table_size(stable) >= set_table_size(otable)) {
            /* Swap so we iterate over the smaller set */
            otable = stable;
            set = other;
        }

        *NEW_PARTIAL_MEMO_FOR(struct set_intersection_data, data, into) = (struct set_intersection_data) {
            .set = new_set,
            .other_set = other,
            .new_set = new_set,
            .into = ntable,
            .other = otable,
        };
        set_iter(set, set_intersection_i, (st_data_t)data);
    }
    else {
        *NEW_PARTIAL_MEMO_FOR(struct set_intersection_data, data, into) = (struct set_intersection_data) {
            .set = new_set,
            .other_set = other,
            .new_set = new_set,
            .into = ntable,
            .other = stable,
        };
        rb_block_call(other, enum_method_id(other), 0, 0, set_intersection_block, data);
    }
    RB_GC_GUARD(data);

    return new_set;
}