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: goto_binary_serde.rs
    path of file: ./repos/kani/cprover_bindings/src/irep
    
    the code of the file until where you have to start completion: // Copyright Kani Contributors
// SPDX-License-Identifier: Apache-2.0 OR MIT
//! GOTO binary serializer.

use crate::irep::{Irep, IrepId, Symbol, SymbolTable};
use crate::{InternString, InternedString};
use std::collections::Hash
    
    fn get_or_insert(&mut self, key: &IrepKey) -> NumberedIrep {
        if let Some(number) = self.cache.get(key) {
            // Return the NumberedIrep from the inverse cache
            return self.inv_cache.index[*number];
        }
        // This is where the key gets its unique number assigned.
        let number = self.inv_cache.add_key(&key);
        self.cache.insert(key.clone(), number);
        self.inv_cache.index[number]
    }