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Subject: Re: [boost] [Root Pointer] New Documentation
From: Phil Bouchard (philippeb8_at_[hidden])
Date: 2016-04-10 22:46:45

On 04/10/2016 09:58 PM, Vladimir Batov wrote:
> I have not looked at the implementation but from the design description
> I suspect I know the answer. The core design decision (if I've got it
> right) is that all node_ptrs are freed when its root_ptr goes out of
> scope irrespectively of cycles or still legitimate references. Yes, it
> solves the cyclic references... but also it invalidates all other
> references.

Sorry for the delay on this, I had to double check on Linux and Windows
before answering and I ended up with this test case:

struct A
     int i;

     A(int i) : i(i)
         std::cout << BOOST_CURRENT_FUNCTION << ": " << i << std::endl;

         std::cout << BOOST_CURRENT_FUNCTION << ": " << i << std::endl;

node_ptr<A> get_int()
      root_ptr<A> r = make_root<A>(9);
      node_ptr<A> p = make_node<A>(r, 10);

      return p;

int main()
     node_ptr<A> p = get_int();
     std::cout << p->i << std::endl;

And it outputs:

A::A(int): 9
A::A(int): 10
A::~A(): 9
A::~A(): 10

But yes the behavior is undefined in this particular case so I need to
write this down in the docs. Thanks Artyom...!

> Well, I've noticed you tend to make quite grandiose statements like "50
> years wondering about GC", "People do not use" and "C++ will need". If I
> were you, I'd certainly refrain from those -- they add nothing but might
> show you in unfavorable light. Because if you and I disappear from the
> face of the earth tomorrow, the humankind, IT and C++ won't be left to
> "wonder for 50 years about" anything. Trust me.

Sorry I used the wrong wording but let's just say that the stakes are high.

> Secondly, I work with networks/graphs. I do not use GC and C++ handles
> that "complexity" just fine. In fact, if I had to name an area which I'd
> label with the "complexity" tag, it would not be the memory management.

The same goal we all have is to write as few lines of code as possible
for a given task. If I can prove that by using root_ptr, the code will
be simpler then I think I will have made my point.

>> There is a minimum of explicitness that needs to be done by the
>> programmer.
> That argument is as good for shared_ptr/weak_ptr combination as it's
> good for root_ptr/node_ptr... If I were forced to deploy one or the other.
>> Because letting the entire memory being managed implicitly results in
>> slow performance like we see with Java or Javascript.
> Well, we are not in Java. And from C++ perspective your statement is so
> wrong that I do not know even where to begin. :-) But that's a different
> altogether topic.

Well for example it is obvious a pool of objects of the same type is
must faster than a pool of objects of any size but you need to call the
right pool explicitly.

But it's like you are saying one solution moves the problem somewhere else:
- the GC is 100% implicit but you need "finalizers"
- shared_ptr needs a weak_ptr to handle cycles
- root_ptr needs a node_ptr and has potential undefined behaviors

At the end of the day it's all about the most commonly used use cases
and if the library can:
- reduce the amount of lines of codes
- is more efficient or not
- is more robust or not
- is more extensible or not

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