Doing one last thing to a WeakReference - Java
This is a discussion on Doing one last thing to a WeakReference - Java ; Stefan Ram wrote:
> Tom Anderson <twic@urchin.earth.li> writes:
>> I think the best accomodation that could be made without a major and
>> potentially awkward addition to the language and runtime system would be a
>> C#-style 'using' construct:
>> ...
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Re: Doing one last thing to a WeakReference
Stefan Ram wrote:
> Tom Anderson <twic@urchin.earth.li> writes:
>> I think the best accomodation that could be made without a major and
>> potentially awkward addition to the language and runtime system would be a
>> C#-style 'using' construct:
>> using (ImageInfo info = getImageInfo(fileName)) {
>> int w = info.getWidth() ;
>> // etc
>> }
>
> In [1], it is described how to write a class
> »FileInputStreamOpenCloseAndNull« so that
>
> for( final java.io.FileInputStream fileInputStream:
> new FileInputStreamOpenCloseAndNull( "input.txt" ))
> use( fileInputStream );
>
> will close »fileInputStream« after the use.
The same can be achieved with a finally.
Arne
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Re: Doing one last thing to a WeakReference
John W Kennedy wrote:
> Stefan Ram wrote:
>> "Paul J. Lucas" <paul-nospam@nospam.lucasmail.org> writes:
>>> It's a perfectly reasonable (and common) thing to want to:
>>> a) guarantee an object is destroyed as soon as it's no longer used
>>> (and not "some later time").
>>> b) do one last thing to an object before it's destroyed.
>>
>> C++ has destructors.
>>
>> Are there any other (object-oriented) programming
>> languages with destructors?
>
> Turbo Pascal did; I suppose Delphi does. I daresay any OO language that
> has either a FREE statement/operator or stack-allocated objects will,
> perforce.
All languages with dynamic allocation and no GC, which probably
is about the same as your criteria.
Ada must fell in this category as well.
Arne
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Re: Doing one last thing to a WeakReference
John B. Matthews wrote:
> In article <48642af2$0$5019$607ed4bc@cv.net>,
> John W Kennedy <jwkenne@attglobal.net> wrote:
>> Stefan Ram wrote:
>>> "Paul J. Lucas" <paul-nospam@nospam.lucasmail.org> writes:
>>>> It's a perfectly reasonable (and common) thing to want to:
>>>> a) guarantee an object is destroyed as soon as it's no longer used
>>>> (and not "some later time").
>>>> b) do one last thing to an object before it's destroyed.
>>> C++ has destructors.
>>>
>>> Are there any other (object-oriented) programming
>>> languages with destructors?
>> Turbo Pascal did; I suppose Delphi does. I daresay any OO language that
>> has either a FREE statement/operator or stack-allocated objects will,
>> perforce.
>
> As did Wirth's Object Pascal, but I'm not sure free qualifies as a
> destructor. In contrast, what the OP wants is a user-defined method that
> is called when the storage is actually reclaimed, but at a more
> deterministic time than finalize().
I don't think the argument was that free was a destructor - just that
a language that used free would need a destructor.
Arne
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Re: Doing one last thing to a WeakReference
In article <4865b356$0$90262$14726298@news.sunsite.dk>,
Arne Vajhøj <arne@vajhoej.dk> wrote:
> John B. Matthews wrote:
> > In article <48642af2$0$5019$607ed4bc@cv.net>,
> > John W Kennedy <jwkenne@attglobal.net> wrote:
> >> Stefan Ram wrote:
> >>> "Paul J. Lucas" <paul-nospam@nospam.lucasmail.org> writes:
> >>>> It's a perfectly reasonable (and common) thing to want to:
> >>>> a) guarantee an object is destroyed as soon as it's no longer used
> >>>> (and not "some later time").
> >>>> b) do one last thing to an object before it's destroyed.
> >>> C++ has destructors.
> >>>
> >>> Are there any other (object-oriented) programming
> >>> languages with destructors?
> >> Turbo Pascal did; I suppose Delphi does. I daresay any OO language that
> >> has either a FREE statement/operator or stack-allocated objects will,
> >> perforce.
> >
> > As did Wirth's Object Pascal, but I'm not sure free qualifies as a
> > destructor. In contrast, what the OP wants is a user-defined method that
> > is called when the storage is actually reclaimed, but at a more
> > deterministic time than finalize().
>
> I don't think the argument was that free was a destructor - just that
> a language that used free would need a destructor.
Yes, but the utility was apparent only in retrospect. All the languages
mentioned (Ada, C++, D, Delphi, Java, Object Pascal, Turbo Pascal) are
object-oriented and have destructors in the sense of a method that is
automatically invoked when the object's storage is reclaimed.
Conversely, not all object-oriented languages that can reclaim storage
(by freeing dynamically allocated memory or closing a stack frame) have
the method invocation characteristic of destructors. Wirth & Tessler's
original Object Pascal is a familiar counter-example. IIRC, Turbo Pascal
had just a single destructor.
--
John B. Matthews
trashgod at gmail dot com
home dot woh dot rr dot com slash jbmatthews
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Re: Doing one last thing to a WeakReference
Arne Vajhøj wrote:
> Stefan Ram wrote:
>> In [1], it is described how to write a class
>> »FileInputStreamOpenCloseAndNull« so that
>>
>> for( final java.io.FileInputStream fileInputStream:
>> new FileInputStreamOpenCloseAndNull( "input.txt" ))
>> use( fileInputStream );
>>
>> will close »fileInputStream« after the use.
>
> The same can be achieved with a finally.
Except if "after the use" is not lexically scoped.
- Paul
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