Re: Dynamic languages (again)

On 21 Mar 2006, at 08:40, raimundox wrote:

> In Java, we only have reflection objects, such as Class, Methods,
> those are 'semi'-Runtime-MOP. You could only read meta-info from those
> things.

This is typically called introspection. Java doesn't provide  
intercession, which is the other "half" of reflection, except for the  
somewhat simplistic dynamic proxy classes, which don't work too bad  
given the constraints of Java.

> Some other framework provide some full MOP thing, but those
> things are not working well

That's nonsense. I use the CLOS MOP extensively in my own work, and  
know quite a few people who use it as well in their own projects. It  
works like a charm. I hear similar things being said about  
Smalltalk's MOP by people who use it extensively (although  
Smalltalk's MOP is not as worked out as the CLOS MOP, but it is also  
far from being as simplistic as Java's). The same is probably true  
for MOPs of other programming languages. (It's correct that a "full"  
MOP is independent from the fact whether a language is dynamic or  
not, but it also seems to be true that it is more likely that you  
find MOPs in dynamic languages. It just seems to be more "natural" to  
go that route in a dynamic language.)


Pascal

> On 3/21/06, cao jing <[email protected]> wrote:
>> so, runtime MOP and runtime metaobjects do not belong to dynamic  
>> languages
>> only, static languages also can have runtime MOP.
>> i think maybe JAVA just has some runtime metaobjects. In java,  
>> does every
>> class exist as a metaobject?
>>
>> 2006/3/21, Jim Haungs <[email protected]>:
>>> There's nothing inherently reflective about dynamic languages,  
>>> nor vice
>> versa. The concepts are orthogonal.
>>>
>>> Dynamic (at least in my definition) means that variables are  
>>> bound to
>> values at run-time, and methods are dispatched via run-time look- 
>> up. True,
>> this requires the VM to introspect the method dictionaries, but  
>> nothing
>> requires the running user-level program to actively introspect  
>> anything.
>>>
>>> And Java has reflection without fully-dynamic typing. By "not
>> fully-dynamic" I mean you can declare a variable to be of type  
>> Object, and
>> put any reference type in there, but you can't put an unboxed  
>> primitive in
>> there, something you can do in Smalltalk and Ruby because everything
>> inherits from Object, even so-called "primitives."
>>>
>>>
>>>
>>> On 3/20/06, Cristina Videira Lopes < [email protected]> wrote:
>>>>
>>>>
>>>> Let me second the last sentence of the previous message. As a  
>>>> dynamic
>> reflective language, Ruby rocks! It's really cute. And it's quite  
>> amazing
>> what people are doing with it -- if you're into learning about it,  
>> don't
>> miss Ruby on Rails. I recently taught an undergrad course on PLs,  
>> where I
>> used Ruby at some point. The students were fascinated.
>>>>
>>>> (I have objections about some of the assumptions behind reflective
>> languages, in general, but that's another story...)
>>>>
>>>>
>>>>
>>>> ________________________________
>>  From: [email protected] [mailto:[email protected]]  
>> On Behalf
>> Of Jim Haungs
>>>> Sent: Monday, March 20, 2006 8:06 AM
>>>> To: Pascal Costanza
>>>> Cc: cao jing; [email protected]
>>>> Subject: Re: [aosd-discuss] discuss Digest, Vol 30, Issue 7
>>>>
>>>>
>>>> In Smalltalk, dynamic typing and dynamic dispatch are closely  
>>>> related.
>> In Smalltalk, variables are merely slots for pointers; they can hold
>> anything. Everything is an Object, including booleans, integers  
>> and strings,
>> even blocks of code.
>>>>
>>>> When a message is sent to an object in a slot, the message name is
>> looked up dynamically, and if a matching method is found, it is  
>> executed.
>> This sounds egregiously slow, but good VM's play all sorts of  
>> tricks to
>> optimize the overhead away.
>>>>
>>>> It's also possible to handle the doesNotUnderstand: error raised  
>>>> by the
>> VM when an appropriate method is not found, yielding delicious  
>> possibilities
>> like faulting an object into memory from a database and then  
>> returning to
>> the original failed call with the correct object now reified.
>>>>
>>>> If you think Smalltalk is interesting but passe, check out Ruby.  
>>>> It's
>> basically Smalltalk reincarnated as a scripting language.
>>>>
>>>>
>>>> On 3/20/06, Pascal Costanza <[email protected]> wrote:
>>>>>
>>>>> On 20 Mar 2006, at 02:10, cao jing wrote:
>>>>>
>>>>>> so, i think SMALLTALK is a kind of Dynamic language, right?
>>>>>
>>>>> Definitely yes.
>>>>>
>>>>>> or, maybe SMALLTALK has some features of static languages, if
>>>>>> it has, then what are they?
>>>>>
>>>>> Since Smalltalk allows you to change almost anything at runtime,
>>>>> including the class hierarchy, method definitions, etc., it's  
>>>>> hard to
>>>>> state that anything about Smalltalk is static. However, I am no
>>>>> expert about Smalltalk, it may be that some things you can do have
>>>>> implications that I am not aware which would render them as
>>>>> practically static. It may be a better idea to ask these  
>>>>> questions in
>>>>> a Smalltalk-related mailing list or newsgroup, like
>> comp.lang.smalltalk.
>>>>>
>>>>>> BTW, is dynamic typing  the main feature  of  Dynamic language?
>>>>>
>>>>> It's certainly one of the main features. Dynamic dispatch is  
>>>>> another
>>>>> one.
>>>>>
>>>>>
>>>>> Pascal
>>>>>
>>>>> --
>>>>> Pascal Costanza, mailto:[email protected], http://p-cos.net
>>>>> Vrije Universiteit Brussel, Programming Technology Lab
>>>>> Pleinlaan 2, B-1050 Brussel, Belgium
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> __________________________________________________
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>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
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>
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-- 
Pascal Costanza, mailto:[email protected], http://p-cos.net
Vrije Universiteit Brussel, Programming Technology Lab
Pleinlaan 2, B-1050 Brussel, Belgium





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