如何通过变量指定位字符串的类型

{FirstPart, Rest} = case Type of
                        {'bitstring', Len} ->
                            <<A:Len/bitstring, B/bitstring>> = Bin,
                            {A,B};
                        'integer' ->
                            <<A/integer, B/bitstring>> = Bin,
                            {A,B};
                        ...

我看不出有什么特别的地方会给处理不同的“类型”编码带来条件上的不便。

case StringType of
  byte_len ->
    <<Len:8, String:Len/binary>> = SomeBinary,
    String;
  word_len ->
    <<Len:32, String:Len/binary>> = SomeBinary,
    String;
  etc -> ...
end