You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: roll_down.rs
    path of file: ./repos/nushell/crates/nu-cmd-extra/src/extra/filters/roll
    
    the code of the file until where you have to start completion: use nu_engine::CallExt;
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol
    
    fn signature(&self) -> Signature {
        Signature::build(self.name())
            // TODO: It also operates on List
            .input_output_types(vec![(Type::Table(vec![]), Type::Table(vec![]))])
            .named("by", SyntaxShape::Int, "Number of rows to roll", Some('b'))
            .category(Category::Filters)
    }