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Home » U++ Library support » U++ Core » why not "T & Add(const T & x)" in all containers
why not "T & Add(const T & x)" in all containers [message #27700] Thu, 29 July 2010 22:17 Go to next message
kohait00 is currently offline  kohait00
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just a short question:

i noticed that all containers dont return a ref on the item created inside a container, when a copy Add is used: (here Array is example)

	T&       Add();
	void     Add(const T& x); //why void?
	void     AddPick(pick_ T& x); //why void?
	T&       Add(T *newt);


so why not having

	T&       Add();
	T&       Add(const T& x);
	T&       AddPick(pick_ T& x);
	T&       Add(T *newt);

the added elements in any case end up in the container, so their ref could be returned...

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Re: why not "T & Add(const T & x)" in all containers [message #27779 is a reply to message #27700] Tue, 03 August 2010 11:15 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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any comments on this?

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Re: why not "T & Add(const T & x)" in all containers [message #27787 is a reply to message #27779] Tue, 03 August 2010 12:53 Go to previous messageGo to next message
andrei_natanael is currently offline  andrei_natanael
Messages: 262
Registered: January 2009
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Hi,

That would be possible but we will lose some performance for nothing(or less). Taking the following code from Array implementation:
	void     Add(const T& x)            { vector.Add(DeepCopyNew(x)); }
	void     AddPick(pick_ T& x)        { vector.Add(new T(x)); }

to return the reference to added element, we have to find the element in vector, and that will take some time.

Andrei

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Re: why not "T & Add(const T & x)" in all containers [message #27793 is a reply to message #27787] Tue, 03 August 2010 16:06 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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why then, not do the same as in 
	T&       Add()                      { T *q = new T; vector.Add(q); return *q; }
//like this
	void     Add(const T& x)            { T *q = DeepCopyNew(x); vector.Add(q); return *q; }
	void     AddPick(pick_ T& x)        { T *q = new T(x); vector.Add(q); return *q; }

the reference does not change, it's stored on heap, there should be no performance hit on that i think.

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Re: why not "T & Add(const T & x)" in all containers [message #27798 is a reply to message #27793] Tue, 03 August 2010 22:44 Go to previous messageGo to next message
andrei_natanael is currently offline  andrei_natanael
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That seems ok.

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Re: why not "T & Add(const T & x)" in all containers [message #27801 is a reply to message #27798] Wed, 04 August 2010 09:57 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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i changed things for Add semantic, take a look at it. it was no much work. maybe mirek has had something special in mind with void return.. i'll ask him.

another thing to be changed is maybe the void Set(int i, const T& x, int count = 1); behaviour. which also could be split up just like Insert..

EDIT: no one has downloaded previous version, so i just change it for one, where Insert and Set behaviour is already changed accordingly. plrese review it. maybe it can go upstream if nothing stands in way.
  • Attachment: Core.rar
    (Size: 12.62KB, Downloaded 273 times)

[Updated on: Wed, 04 August 2010 11:23]

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Re: why not "T & Add(const T & x)" in all containers [message #27810 is a reply to message #27801] Thu, 05 August 2010 08:35 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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any comments on that one? (need it for my app Smile, like always...)

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Re: why not "T & Add(const T & x)" in all containers [message #27812 is a reply to message #27810] Thu, 05 August 2010 09:55 Go to previous messageGo to next message
mrjt is currently offline  mrjt
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I'd like to hear Mirek's reasons for doing it the old way because there is usually a good reason, especially for the NTL stuff.

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Re: why not "T & Add(const T & x)" in all containers [message #27814 is a reply to message #27812] Thu, 05 August 2010 10:10 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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ofcorse. i also was trying to imagine what problems there might be to have prevented this stuff to already be there. nevertheless wanted to provide already a solution to think visually about Smile.

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Re: why not "T & Add(const T & x)" in all containers [message #27844 is a reply to message #27700] Fri, 06 August 2010 11:27 Go to previous messageGo to next message
mirek is currently offline  mirek
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kohait00 wrote on Thu, 29 July 2010 16:17

just a short question:

i noticed that all containers dont return a ref on the item created inside a container, when a copy Add is used: (here Array is example)

	T&       Add();
	void     Add(const T& x); //why void?
	void     AddPick(pick_ T& x); //why void?
	T&       Add(T *newt);




Mostly because of standard usage pattern...

It might be a little bit confusing as those variants that are taking parameter make a copy of this parameter (and would return a reference to this copy).

Also note the existence of Top() - only one more line...

But I am not strongly opposed to changing this either....

[Updated on: Fri, 06 August 2010 11:30]

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Re: why not "T & Add(const T & x)" in all containers [message #27847 is a reply to message #27844] Fri, 06 August 2010 11:48 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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the usage pattern is not changed too much in fact. all the functions changed (in code provided) returned void by before. so it's more of an extension..

the 'new' usage pattern would be, get direct access to the object, that 'somehow' has been added / replaced (Set) / or inserted. because it exists in container after the call, beeing it the same or a copy, the user wouldnt need to care. it is the one that remains in the container (maybe could even be more logic).

this would spare the usage of Top() or even operator[](GetCount()-1) like in some places, after having void Add(const & T x). this by the way uses the rather 'implicit' assumption that an added item is always placed last...

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Re: why not "T & Add(const T & x)" in all containers [message #27878 is a reply to message #27847] Mon, 09 August 2010 08:50 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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to which conclusion have you guys come? should it be extended?

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Re: why not "T & Add(const T & x)" in all containers [message #27998 is a reply to message #27878] Fri, 13 August 2010 09:38 Go to previous messageGo to next message
mirek is currently offline  mirek
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kohait00 wrote on Mon, 09 August 2010 02:50

to which conclusion have you guys come? should it be extended?


I am barely positive about this, but before I waste time fixing documentation, I still cannot imagine usage scenario which I would like - I think that you either use Vector to store "values" and then you do not need those references as return values, or to create objects inside.

I mean, just tell me little where it does help Smile Practical example is most welcome.

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Re: why not "T & Add(const T & x)" in all containers [message #28101 is a reply to message #27998] Mon, 16 August 2010 09:06 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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it's actually the same behaviour as with T& Array::Attach(T* newt);
and merly a logical unification of interface, that anything that ends beeing an object, no matter newly added or as copy, should be instantly available, without the need to again access the container to get the same. here, it actually doesnt matter the container type, it's same situation for Vector and Array.

a practical use is this:

crating new container objects, based on some 'template' objects, and remodifying stuff that is actually different, on the new created object, pushing it somewhere to do something. this would use in case of Array:
void Array::Add(cibst T&),
then
T& Array::operator[](int i) with Array::GetCount()-1.
actually 3 invokations, that could be done in one.

it's maybe more of estetic use Smile but could again add to Ultimate's short and reading friendly code

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Re: why not "T & Add(const T & x)" in all containers [message #28347 is a reply to message #28101] Mon, 30 August 2010 10:46 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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hey mirek, what is your final decision on this one?
sorry if disturbing in vacations Smile

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Re: why not "T & Add(const T & x)" in all containers [message #28533 is a reply to message #28101] Mon, 06 September 2010 10:53 Go to previous messageGo to next message
mirek is currently offline  mirek
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kohait00 wrote on Mon, 16 August 2010 03:06

then
T& Array::operator[](int i) with Array::GetCount()-1.
actually 3 invokations, that could be done in one.



Could be done with Top().

I am likely to make this change, but I am still waiting for 3rd party opinion...

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Re: why not "T & Add(const T & x)" in all containers [message #28536 is a reply to message #28533] Mon, 06 September 2010 11:52 Go to previous messageGo to next message
kohait00 is currently offline  kohait00
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who is 3rd party? Cool

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Re: why not "T & Add(const T & x)" in all containers [message #28588 is a reply to message #28536] Wed, 08 September 2010 09:00 Go to previous messageGo to next message
mirek is currently offline  mirek
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Not me and not you Smile (That makes it 3rd, right?)

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Re: why not "T & Add(const T & x)" in all containers [message #28605 is a reply to message #28588] Wed, 08 September 2010 10:24 Go to previous messageGo to next message
rylek is currently offline  rylek
Messages: 79
Registered: November 2005
Member
Hi there!

It is a pleasure to play the third party, though the semantics of the term are highly disputable here. I think it's possible Mirek originally didn't include the return reference in Vector::Add to emphasize the fact that such references into Vectors are volatile in principle (specifically they are periodically invalidated by the Add function itself while reallocating the physical Vector data). But, of course, the same argument holds for Add() which does return the reference. Moreover, Array::Add(T *newobj) also returns the reference, albeit for different reasons.

U++ also decidedly avoids returning references in pick assignment operators, which is natural because a "chain" assignment (a = b = c) in such cases exhibits undesirable behaviour (by destroying b). But Vector::Add(const T&) doesn't have this problem; the only thing that has to be avoided is rather artificial constructs of the form

vector.Add(vector.Add(obj))


exactly because of the periodical Vector reference invalidation. But then again you can run into exactly the same problems by writing, e.g.

vector.Add(vector[5]);


so that this is no specific of Vector::Add(const T&) either. To sum it all up, I currently see no practical reasons against modifying Vector::Add to include the return reference. I would rather say that it's like updating old code to match interface standards adopted / developed later on, in fact I believe Vector is one of the very oldest things in U++ (although it's been rewritten quite a few times since its inception).

Regards

Tomas

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Re: why not "T & Add(const T & x)" in all containers [message #28611 is a reply to message #28605] Wed, 08 September 2010 10:54 Go to previous messageGo to previous message
kohait00 is currently offline  kohait00
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thanks, nice outline

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