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: mutator.rs
    path of file: ./repos/differential-datalog/rust/template/ddlog_derive/src
    
    the code of the file until where you have to start completion: use super::{add_trait_bounds, get_rename};
use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote};
use syn::{
    parse_quote, spanned::Spanned, Data, DataEnum, DataStruct, DeriveInput, Error, Fields,
    FieldsNamed, FieldsUnnamed, Ident, ImplGenerics, Index, Result, TypeGenerics, WhereClause,
};

pub fn mutator_inner(mut inp
    
            fn mutate_inner(&self, #mutated: &mut #enum_ident #type_generics) -> ::core::result::Result<(), ::std::string::String> {
                match #mutated {
                    #generated_mutators
                    _ => { *#mutated = <#enum_ident #type_generics as ::differential_datalog::record::FromRecord>::from_record(self)?; },
                }

                ::core::result::Result::Ok(())
            }