[erlang-questions] jinterface List vs. String

Robert Raschke <>
Tue Dec 9 11:37:32 CET 2008


Hi Vlad,

thanks for the info.

On Tue, Dec 9, 2008 at 10:15 AM, Vlad Dumitrescu <> wrote:
> Hi,
>
> On Tue, Dec 9, 2008 at 10:54, Robert Raschke <> wrote:
>> does anyone have a good idea on how I can distinguish between a list
>> and a string in jinterface?
>
> The short answer is that you can't without traversing the list/string.
> Since there is no string datatype in Erlang, the two are only
> differentiated by their contents.
>
>> Or, in other words, if jinterface has decided to receive an
>> OtpErlangString (from a sent list like [1, 2, 3], for example), is
>> there an easy way to convert it to an OtpErlangList? I know I can do
>> it by hand, but that's ever so slightly icky.
>
> Actually, it is Erlang that decides to encode a list as a STRING_EXTor
> as a LIST_EXT, as an optimization.
>
> The way to handle that is by expecting either a list or a string and
> convert from each of them to the Java class you're going to use.
> Slightly icky, as you say...
>
> Maybe OtpErlangString should have inherited from OtpErlangList?
>
> best regards,
> Vlad
>

Maybe something like the following could be added to the OtpErlangString class?

  /**
   * Get this Erlang string as an Erlang list of Erlang bytes.
   *
   * @return the list of bytes contained in this string.
   **/
  public OtpErlangList asOtpErlangList() {
    byte[] b = str.getBytes();
    OtpErlangByte[] eb = new OtpErlangByte[b.length];
    for (int i = 0; i < b.length; i++)
      eb[i] = new OtpErlangByte(b[i]);
    return new OtpErlangList(eb);
  }

I haven't done Java in a while, maybe there's a way to "overload" the
cast operator? That would be another way.

Robby



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