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Home » U++ Library support » U++ Core » Core: Null handling incoherent?
| Core: Null handling incoherent? [message #32255] |
Wed, 04 May 2011 10:46  |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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hi all,
i'm wondering why
template <class T> bool IsNull(const T& x) { return x.IsNullInstance(); }
and not
template <class T> bool IsNull(const T& x) { return x.IsNull(); }
is there a reason for it? name clashes??
analogue to upp philosophy it should be latter case, ( Xmlize() { x.Xmlize() } etc.)
some classes define IsNullInstance(), some do IsNull(), it's kinda 'not clean'
(background: i'm tackling Null handling in terms of extension of Value with other types on user side (i.e. float), where the Null handlig is the major problem.)
EDIT:
it's also the point of what Null actually is.. is it only to be seen in context with Value handling? because all classes interacting with Value the classes need to know about Value, but Value.h defines some of the interface handling with the types as well. so it's mixed. (i.e. String.h has template definition of IsNull())..
maybe to think of null handling as kind a independant from Value and define it in Defs.h
template <class T> void SetNull(T& x) { x.SetNull(); }
template <class T> bool IsNull(const T& x) { return x.IsNullInstance(); }
so both, Value.h and all the others are aware of that concept..
this probably would also make sense to move Nuller concept to Defs.h
i'm currently making some changes, just trying to get trhough it properly..
[Updated on: Wed, 04 May 2011 11:22] Report message to a moderator |
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| Re: Core: Null handling incoherent? [message #32256 is a reply to message #32255] |
Wed, 04 May 2011 11:39  |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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attached is a patch for discussion. the IsNullInstance naming issue is not adressed yet.
benefits:
* more clear coherent interface because IsNullInstance, SetNull are obligatory
* users can use RichValue<> as container for even own intrinsic types like float.., specifying themselves the null handling.
(but float f = Null; still wont work, since it has no converter, but SetNull<float>() can, which is a nice price to pay.
* specifying AsString<T> they can use the Value::ToString for it as well, i.e AsString<float> is already specified..
i'd have considered to have
template <class T> void SetNull(T& x) { x = Null; }
to make SetNull method optional, but Null is kind a wired with Value, which, at level of Defs.h isn't known yet..
-
Attachment: patch0.patch
(Size: 5.77KB, Downloaded 220 times)
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| Re: Core: Null handling incoherent? [message #32289 is a reply to message #32284] |
Fri, 06 May 2011 10:43 |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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that's why i tried a second version using the Null assignment (see the second patch) as the the global SetNull usage. the SetNull method as part of class interface besides IsNullInstance and Nuller ctor is not needed in that way.. it's kind a same approach as with global IsNull template.
the global template SetNull would be used by RichValue<> in GetNull(), which prevented the compile for the custom RichValue<float>.. since i couldnt specify additional operator float() in the Nuller (the idea of a template T() operator for Nuller is not practical for ambiguity reasons).
the IsNullInstance question was why there is no unique verision of IsNull API inside Value handled classes. sometimes they are IsNullInstance (which is dictated by IsNull<>) and sometimes it's IsNull, where a template specialisation is needed, like in Font..
is it legacy or should it be unified?
[Updated on: Fri, 06 May 2011 11:07] Report message to a moderator |
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| Re: Core: Null handling incoherent? [message #33788 is a reply to message #33110] |
Tue, 13 September 2011 18:08 |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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hi mirek..
i'm depending on that a bit.. for my bazaar/LogPosCtrl...
take a look at bazaar/Gen/Vtypes.h/.cpp
there, i have Ctrl::LogPos RichValue'ized, which would not be possible without the SetNull template, since it has no from Nuller ctor.
if you are concerned about the several IsNull->IsNullInstance renames, i can provide a patch without it. but it only code cleanup. think of the last release date  we are far away..maybe a good chance to correct things.
for the float problem, i managed to circumvent the Value extension, but this is way more important, cause very general.
moving the things to Defs.h is just clean. since several other classes do depend on the stuff, that otherwise resides scattered in the code. again, the beginner user benefits from it encountering it where expected..
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| Re: Core: Null handling incoherent? [message #33798 is a reply to message #33796] |
Wed, 14 September 2011 12:46 |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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what exactly did you compile? i cant reproduce any unsigned errors..when i try to compile the LogPosCtrlTest, it fails due to SetNull stuff not present...
imho, unsigned is not neccessary for Value..as mirek already lined out in an older thread, where i proposed to enrich value by all signed type.. Value does not care about the sizes of the representation, it cares only about the logic types, beeing bool, integer, and floating point values (represented by whatever highest available precision, bool, int64, double). int is merely from old days..
did you try the set null patch?
EDIT: heres the patch as svn patch again.. for a quick test
again, the changes are not deep, there are some .IsNull to .IsNullInstance renames for clean code base..the rest is block moving and some extensions
[Updated on: Wed, 14 September 2011 13:20] Report message to a moderator |
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| Re: Core: Null handling incoherent? [message #33812 is a reply to message #32255] |
Thu, 15 September 2011 12:57 |
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mirek
Messages: 14255
Registered: November 2005
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Ultimate Member |
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| kohait00 wrote on Wed, 04 May 2011 04:46 |
hi all,
i'm wondering why
template <class T> bool IsNull(const T& x) { return x.IsNullInstance(); }
and not
template <class T> bool IsNull(const T& x) { return x.IsNull(); }
is there a reason for it? name clashes??
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Think about:
void Ctrl::TestSomething()
{
String x = Something();
if(IsNull(x)) ...
}
Mirek
[Updated on: Thu, 15 September 2011 12:57] Report message to a moderator |
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| Re: Core: Null handling incoherent? [message #33815 is a reply to message #33814] |
Thu, 15 September 2011 15:34 |
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mirek
Messages: 14255
Registered: November 2005
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Ultimate Member |
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When IsNull is method, compiler will presume you want to use it instead of global function. That is why method has to have different name.
Well, there might be some IsNull methods somewhere in concrete or special classes still. Not sure this needs fixing. IsNullInstance is contract to make IsNull work without specialized global function.
Mirek
[Updated on: Thu, 15 September 2011 15:38] Report message to a moderator |
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| Re: Core: Null handling incoherent? [message #33817 is a reply to message #33815] |
Thu, 15 September 2011 16:30 |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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ok i was aware of this, but couldnt figure out what you where aiming at with the example..sorry..
this is totally clean approach. thats why the patch contains some fixes of some classes, (Uuid, Font), which use IsNull as member, which doesnt fit cleanly.
sorry for bothering you with this, but i really heavily rely on flexible Value extension for RichValue..and really hope you are alright with the propose or any alternative. since it does not change any semantic. =Null is still default assignment everywhere (the SetNull template is only used in RichValue..and uses =Null approach as inlined default). it offers possibility to override the =Null assignment and try the SetNull where needed, i.e. when using classes in RichValue, specified all from extern (seriliaze, xmlize, gethashvalue, as template specialisations)
i know it's not the full problem solution..is there any other idea?
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