Return a constructor for an encoder for fields of a particular type.

  Args:
      wire_type:  The field's wire type, for encoding tags.
      encode_value:  A function which encodes an individual value, e.g.
        _EncodeVarint().
      compute_value_size:  A function which computes the size of an individual
        value, e.g. _VarintSize().

def _SimpleEncoder(wire_type, encode_value, compute_value_size):
  """Return a constructor for an encoder for fields of a particular type.

  Args:
      wire_type:  The field's wire type, for encoding tags.
      encode_value:  A function which encodes an individual value, e.g.
        _EncodeVarint().
      compute_value_size:  A function which computes the size of an individual
        value, e.g. _VarintSize().
  """

  def SpecificEncoder(field_number, is_repeated, is_packed):
    if is_packed:
      tag_bytes = TagBytes(field_number, wire_format.WIRETYPE_LENGTH_DELIMITED)
      local_EncodeVarint = _EncodeVarint
      def EncodePackedField(write, value):
        write(tag_bytes)
        size = 0
        for element in value:
          size += compute_value_size(element)
        local_EncodeVarint(write, size)
        for element in value:
          encode_value(write, element)
      return EncodePackedField
    elif is_repeated:
      tag_bytes = TagBytes(field_number, wire_type)
      def EncodeRepeatedField(write, value):
        for element in value:
          write(tag_bytes)
          encode_value(write, element)
      return EncodeRepeatedField
    else:
      tag_bytes = TagBytes(field_number, wire_type)
      def EncodeField(write, value):
        write(tag_bytes)
        return encode_value(write, value)
      return EncodeField

  return SpecificEncoder