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: encoder.rs
    path of file: ./repos/rust-bert/src/models/mobilebert
    
    the code of the file until where you have to start completion: // Copyright (c) 2020  The Google AI Language Team Authors, The HuggingFace Inc. team and github/lonePatient
// Copyright 2020 Guillaume Becquin
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//     
    
        let ffn = if num_feedforward_networks > 1 {
            let mut layers = Vec::with_capacity(num_feedforward_networks as usize);
            let p_layers = p / "ffn";
            for layer_index in 0..num_feedforward_networks - 1 {
                layers.push(FFNLayer::new(&p_layers / layer_index, config));
            }
            Some(layers)
        } else {
            None
        };