[Openmcl-devel] Q: Clozure CL and built-in class vs. CLOS class, how to get a CLOS instance from CCL:MAKE-SOCKET?

Mon Jul 8 01:22:09 PDT 2013

Hi Gary,

many thanks for the good explanation! That has helped a lot.

Best regards,

Rainer Joswig

Am 06.07.2013 um 09:06 schrieb Gary Byers <gb at clozure.com>:

> The documentation does mention some things that your code is missing, but
> the explanation is garbled enough that it's not surprising that things
> didn't quite work as expected.
> 
> First of all:
> 
> - a BASIC-STREAM is an instance of one of a fixed set of  built-in classes.
> You can't easily subclass a BASIC-STREAM class, and methods defined on these
> classes may or may not be called by I/O primitives.
> 
> - a FUNDAMENTAL-STREAM is a STANDARD-OBJECT; FUNDAMENTAL-STREAM classes can
>   be subclassed and extended like other standard CLOS objects.  It's expected
>   that FUNDAMENTAL-STREAMS obey a protocol suggested by David Gray ("the Gray
>   Streams protocol") late in the ANSI CL standardization process.  (The
>   relevant email is archived at
> 
>    <ftp://ftp.clozure.com/pub/stream-definition-by-user.mail>
>    or
>    <http://www.clozure.com/FTP/pub/stream-definition-by-user.mail>
> 
> OPEN and CCL:MAKE-SOCKET accept two keyword arguments that affect the
> class of the streams that they create:
> 
>  :BASIC (which default to T) is intended to differentiate between the two
>    cases described above.
> 
>  :CLASS should be a class or class name; a prototype instance of the
>    specified class is used to determine the actual class of the created
>    stream (see below.)
> 
> It's a little anomalous (at least) for :BASIC to default to T and for :CLASS
> to denote a FUNDAMENTAL-STREAM class.  I'm a little surprised that it seems to
> work at all, wouldn't be shocked if it currently didn't work in some cases,
> and wouldn't be shocked if it's considered to be an error in the future.
> 
> A prototype instance of the specified class (the class's CLASS-PROTOTYPE) is
> used to determine a concrete class by calling the method CCL::SELECT-STREAM-CLASS
> with the instance  a boolean indicating whether or not the stream is being opened
> for input, another boolean indication whether it's being opened for output, and
> a third boolean indicating whether the stream will support character (as opposed
> to binary) I/O operations.  This makes more sense in the case of FILE-STREAMs than
> it does on sockets:  the hypothetical abstract class CASE-INVERTING-FILE-STREAM
> may have concrete subclasses CASE-INVERTING-INPUT-FILE-STREAM and CASE-INVERTING-OUTPUT-FILE-STREAM and CASE-INVERTING-IO-FILE-STREAM, and so
> one might define:
> 
> (defmethod ccl::select-stream-class ((s case-inverting-file-stream) in-p out-p char-p)
>  (if char-p
>    (if in-p
>      (if out-p
>        'case-inverting-io-file-stream
>        'case-inverting-input-file-stream)
>      'case-inverting-output-file-stream
>     (call-next-method)))
> 
> For TCP streams - which are generally bidirectional and bivalent - the
> :CLASS argument is more likely to be concrete; a plausible definition
> of the CCL::SELECT-STREAM-CLASS method for FUNDAMENTAL-TCP-STREAM could
> be:
> 
> (defmethod ccl::select-stream-class ((s fundamental-tcp-stream) in-p out-p char-p)
>  (declare (ignorable in-p out-p char-p))
>  (class-name (class-of s)))
> 
> Unfortunately, the actual method always returns the symbol
> FUNDAMENTAL-TCP-STREAM, and your MY-STREAM class inherits this method.
> You'd need to override this method:
> 
> (defmethod ccl::select-stream-class ((s my-stream) in-p out-p char-p)
>  (declare (ignorable in-p out-p char-p))
>  (class-name (class-of s)))
> 
> ? (ccl:make-socket :remote-host "www.apple.com" :remote-port 80 :basic nil :class 'my-stream)
> #<MY-STREAM :ISO-8859-1 (SOCKET/22) #x302002A6E17D>
> ?
> 
> 
> On Sat, 6 Jul 2013, Rainer Joswig wrote:
> 
>> Hi,
>> 
>> okay, I read the documentation.
>> 
>> Welcome to Clozure Common Lisp Version 1.8-store-r15418  (DarwinX8664)!
>> ? (apropos "fundamental-tcp")
>> CCL::FUNDAMENTAL-TCP-STREAM
>> 
>> ? (defclass my-stream (CCL::FUNDAMENTAL-TCP-STREAM) ())
>> #<STANDARD-CLASS MY-STREAM>
>> 
>> ? (ccl:make-socket :remote-host "www.apple.com" :remote-port 80 :class 'my-stream)
>> #<FUNDAMENTAL-TCP-STREAM :ISO-8859-1 (SOCKET/10) #x3020010FE43D>
>> 
>> In above call it returns a CLOS stream of class CCL::FUNDAMENTAL-TCP-STREAM , but I would have expected that it uses the class argument - given the CCL documentation in chapter 10.1.2 .
>> 
>> Is there anything I'm doing wrong?
>> 
>> Regards,
>> 
>> Rainer Joswig
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> Am 05.07.2013 um 11:51 schrieb Gary Byers <gb at clozure.com>:
>> 
>>> If there were manual sections that answered these questions, I bet that
>>> they'd be called "10.1.2" and "10.1.3". I suppose that those sections
>>> could address some aspects of what they discuss more clearly than they
>>> do, but it'd probably be more productive to ask any remaining questions
>>> after reading those sections than to not do so ...
>>> 
>>> On Fri, 5 Jul 2013, Rainer Joswig wrote:
>>> 
>>>> Hi,
>>>> 
>>>> 
>>>> I'm currently using Clozure CL on two types of tiny ARM computers under Linux: Raspberry Pi and Odroid-X2. I have to say, it really rocks. Many thanks for the fantastic ARM port!
>>>> 
>>>> While trying to port some code to Clozure CL I was a bit thinking about the following:
>>>> 
>>>> If I create a socket with CCL:MAKE-SOCKET , I then get an instance of built-in class CCL::BASIC-TCP-STREAM .
>>>> 
>>>> Interestingly enough this built-in class also inherits from a CLOS class CCL::TCP-STREAM, plus two built-in streams.
>>>> 
>>>> For the particular functionality I would like to have a CLOS-based TCP-STREAM, so that I can write my own subclass and also can use CHANGE-CLASS.
>>>> 
>>>> Now I have the following questions:
>>>> 
>>>> * why is CCL::BASIC-TCP-STREAM not a CLOS class? Wouldn't it be more useful for the developer?
>>>> 
>>>> * how can I use CCL:MAKE-SOCKET so that it returns a CLOS class?
>>>> 
>>>> * are there other easy ways to get a socket as a CLOS class?
>>>> 
>>>> 
>>>> Regards,
>>>> 
>>>> Rainer Joswig
>>>> 
>>>> 
>>>> 
>>>> 
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>>>> Openmcl-devel at clozure.com
>>>> http://clozure.com/mailman/listinfo/openmcl-devel
>>>> 
>>>> 
>> 
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