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digitalmars.D.bugs - [Issue 9601] New: Make regular D objects on closures

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9601

           Summary: Make regular D objects on closures
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: verylonglogin.reg gmail.com



12:57:11 MSK ---
The idea is to make created delegate data pointer referring to a valid D object
just like for class member function.

It will allow passing closure delegate to functions where such objects are
expected and controlling/watching delegate lifetime.

Once it will be implemented the only "raw" delegates would be struct member
function delegates? which are used rarely and can easily be avoided.

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next sibling parent d-bugmail puremagic.com writes:
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Maxim Fomin <maxim maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxim maxim-fomin.ru



---


 The idea is to make created delegate data pointer referring to a valid D object
 just like for class member function.
 
 It will allow passing closure delegate to functions where such objects are
 expected and controlling/watching delegate lifetime.
 
 Once it will be implemented the only "raw" delegates would be struct member
 function delegates? which are used rarely and can easily be avoided.


Please elaborate on "to make created delegate data pointer referring to a valid
D object just like for class member function". I see no point here since it is
always possible to do:

delegate dg = ...;
dg.ptr = whatever is valid - class for member-function, frame for non-member
one
dg()

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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19:51:10 MSK ---


 Please elaborate on "to make created delegate data pointer referring to a valid
 D object just like for class member function".


As it looks like a proper way to allow "controlling/watching delegate lifetime"
as I wrote. And such ability is essential to fix e.g. Phobos Issue 9603 and
make a small but fundamental step forward to working signals in D. Also see
Issue 9602.


 I see no point here since it is
 always possible to do:
 
 delegate dg = ...;
 dg.ptr = whatever is valid - class for member-function, frame for non-member
 one
 dg()


I do not understand you example at all.

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---




 Please elaborate on "to make created delegate data pointer referring to a valid
 D object just like for class member function".


 
 As it looks like a proper way to allow "controlling/watching delegate lifetime"
 as I wrote. And such ability is essential to fix e.g. Phobos Issue 9603 and
 make a small but fundamental step forward to working signals in D. Also see
 Issue 9602.
 


You probably mean data pointer of delegate since delegate does not have
lifetime. Still do not understand what exactly you are proposing.

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---


 The idea is to make created delegate data pointer referring to a valid D object
 just like for class member function.


Since creation delegate data pointer points to valid memory forgetting about
tricks to deliberatly break it. Problem may come when i.e. class destructor
references such object which was collected already by GC. But pointer should be
reset to null. This actually is a problem of class destructor synchronizing.
Are you targeting at this problem?


 It will allow passing closure delegate to functions where such objects are
 expected and controlling/watching delegate lifetime.


How do you suggest to pass information within delegate about data lifetime? Or
what mechanism (in addition to GC) would ensure that?


 Once it will be implemented the only "raw" delegates would be struct member
 function delegates? which are used rarely and can easily be avoided.


If such delegate references this struct pointer it may lead to trouble.
Otherwise what is specific to struct delegates?

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20:09:50 MSK ---


 You probably mean data pointer of delegate since delegate does not have
 lifetime.


I propose to define an "object" delegate's lifetime to be its data pointer
lifetime.


 Still do not understand what exactly you are proposing.


OK. I added an example, see Comment 2 Issue 9603.

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20:21:58 MSK ---




 The idea is to make created delegate data pointer referring to a valid D object
 just like for class member function.


 
 Since creation delegate data pointer points to valid memory forgetting about
 tricks to deliberatly break it. Problem may come when i.e. class destructor
 references such object which was collected already by GC. But pointer should be
 reset to null. This actually is a problem of class destructor synchronizing.
 Are you targeting at this problem?


No. I'm targeting the problem when delegate's outer scope is destroyed and the
problem of determining that the delegate will live "forever" (no "destroyable"
outer scope). See example suggested in my previous post.


 It will allow passing closure delegate to functions where such objects are
 expected and controlling/watching delegate lifetime.


 
 How do you suggest to pass information within delegate about data lifetime? Or
 what mechanism (in addition to GC) would ensure that?


This is trivial. When creating a closure allocate a special D class instead,
that's all. I.e. add a few hidden D object fields before closure data. We will
have something like member function delegate then.


 Once it will be implemented the only "raw" delegates would be struct member
 function delegates? which are used rarely and can easily be avoided.


 
 If such delegate references this struct pointer it may lead to trouble.
 Otherwise what is specific to struct delegates?


Yes, struct pointer delegates will still be troubles unless D struct will
contain regular D object hidden fields defining it being a "struct object". I
see no good solution for this problem now. But as I have never meet with such
difficulties I don't think it is near as high priority issue as closure
delegates.

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---






 The idea is to make created delegate data pointer referring to a valid D object
 just like for class member function.


 
 Since creation delegate data pointer points to valid memory forgetting about
 tricks to deliberatly break it. Problem may come when i.e. class destructor
 references such object which was collected already by GC. But pointer should be
 reset to null. This actually is a problem of class destructor synchronizing.
 Are you targeting at this problem?


 
 No. I'm targeting the problem when delegate's outer scope is destroyed and the
 problem of determining that the delegate will live "forever" (no "destroyable"
 outer scope). See example suggested in my previous post.


I see. This should have been clarified in the very first comment.



 Once it will be implemented the only "raw" delegates would be struct member
 function delegates? which are used rarely and can easily be avoided.


 
 If such delegate references this struct pointer it may lead to trouble.
 Otherwise what is specific to struct delegates?


 
 Yes, struct pointer delegates will still be troubles unless D struct will
 contain regular D object hidden fields defining it being a "struct object". I
 see no good solution for this problem now. But as I have never meet with such
 difficulties I don't think it is near as high priority issue as closure
 delegates.


Actually there is issue 9352.

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