code: public static MappedBytes allocate(File file, FileChannel.MapMode mode, int size) {
      return FileBytes.allocate(file, size).map(0, size, mode);
    }
docs: Allocates a mapped buffer.
  <p>
  Memory will be mapped by opening and expanding the given {@link File} to the desired {@code count} and mapping the
  file contents into memory via {@link FileChannel#map(FileChannel.MapMode, long, long)}.
  
  @param file The file to map into memory. If the file doesn't exist it will be automatically created.
  @param mode The mode with which to map the file.
  @param size The count of the buffer to allocate (in bytes).
  @return The mapped buffer.
  @throws NullPointerException     If {@code file} is {@code null}
  @throws IllegalArgumentException If {@code count} is greater than {@link Integer#MAX_VALUE}
  @see #allocate(File, int)