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: variable_size.rs
    path of file: ./repos/tensorbase/crates/arrow/src/array/transform
    
    the code of the file until where you have to start completion: // Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use crate::{
    array::{ArrayData, OffsetSizeTrait},
    buffer::MutableBuffer,
};

use super::{
    Extend, _MutableArrayData,
    utils::{extend_offsets, get_last_offset},
};

#[inline]
fn extend_offset_values<T: OffsetSizeTrait>(
    buffer: &mut MutableBuffer,
    offsets: &[T],
    values: &[u8],
    start: usize,
    len: usize,
) {
    let start_values = offsets[start].to_usize().unwrap();
    let end_values = offsets[start + len].to_usize().unwrap();
    let new_values = &values[start_values..end_values];
    buffer.extend_from_slice(new_values);
}

pub(super) fn build_extend<T: OffsetSizeTrait>(array: &ArrayData) -> Extend {
    let offsets = array.buffer::<T>(0);
    let values = array.buffers()[1].as_slice();
    if array.null_count() == 0 {
        // fast case where we can copy regions without null issues
        Box::new(
            move |mutable: &mut _MutableArrayData, _, start: usize, len: usize| {
     
    
pub(super) fn build_extend<T: OffsetSizeTrait>(array: &ArrayData) -> Extend {
    let offsets = array.buffer::<T>(0);
    let values = array.buffers()[1].as_slice();
    if array.null_count() == 0 {
        // fast case where we can copy regions without null issues
        Box::new(
            move |mutable: &mut _MutableArrayData, _, start: usize, len: usize| {
                let offset_buffer = &mut mutable.buffer1;
                let values_buffer = &mut mutable.buffer2;

                // this is safe due to how offset is built. See details on `get_last_offset`
                let last_offset = unsafe { get_last_offset(offset_buffer) };

                extend_offsets::<T>(
                    offset_buffer,
                    last_offset,
                    &offsets[start..start + len + 1],
                );
                // values
                extend_offset_values::<T>(values_buffer, offsets, values, start, len);
            },
        )
    } else {
        Box::new(
            move |mutable: &mut _MutableArrayData, _, start: usize, len: usize| {
                let offset_buffer = &mut mutable.buffer1;
                let values_buffer = &mut mutable.buffer2;

                // this is safe due to how offset is built. See details on `get_last_offset`
                let mut last_offset: T = unsafe { get_last_offset(offset_buffer) };

                // nulls present: append item by item, ignoring null entries
                offset_buffer.reserve(len * std::mem::size_of::<T>());

                (start..start + len).for_each(|i| {
                    if array.is_valid(i) {
                        // compute the new offset
                        let length = offsets[i + 1] - offsets[i];
                        last_offset += length;

                        // append value
                        let bytes = &values[offsets[i].to_usize().unwrap()
                            ..offsets[i + 1].to_usize().unwrap()];
                        values_buffer.extend_from_slice(bytes);
                    }
                    // offsets are always present
                    offset_buffer.push(last_offset);
                })
            },
        )
    }
}