creating a shared_ptr<T> from a weak_ptr<T>

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Re: [Boost-Users] AllExamples.dsw...

Toon Knapen

4 May 2002 4 May '02

7:49 p.m.

When creating a shared_ptr<T> from a weak_ptr<T>, I want the shared_ptr<T> to use the same count as the shared_ptr the weak_ptr was constructed from. I could create a new shared_ptr, based on the pointer I can get() from the weak_ptr. But in this case, this shared_ptr will keep its own count. Let me fill you in on my use-case. An object creates some big data-structure on request of its clients, taking into account some options specified by the client while making the request. Now I'd like the server-object to keep a weak_ptr to these big data-structure to provide quickly the same result once another client performs an identical request. The server should however not keep a shared_ptr because otherwise all datastructure will stay in memory. And therefor I need to create a shared_ptr from a weak_ptr. thanks, toon

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Peter Dimov

4 May 4 May

2:12 p.m.

New subject: [Boost-Users] creating a shared_ptr<T> from a weak_ptr<T>

From: "Toon Knapen"

...

When creating a shared_ptr<T> from a weak_ptr<T>, I want the shared_ptr<T> to use the same count as the shared_ptr the weak_ptr was constructed from.

The CVS shared_ptr has a constructor that takes a weak_ptr and will attach to the original count (or throw an exception if this isn't possible, as the object has already been deallocated.)

hicks

6 May 6 May

4:13 a.m.

New subject: Query regarding the use/limitiations of traits in metaprogramming

Query regarding the use/limitiations of traits in metaprogramming I am trying to use traits pattern to assist in metaprogramming. I have the following problem. A traits class "trait" defers a decision to another traits class "trait1" depending on the result of a third traits class "traita". However, the compiler does not cooperate. The code below excutes but gives unexpected output (also shown). [Note:: The code has been reduced to the minimal to demonstrate the problem. I have a real task at hand not shown here.] template <class T> struct traita { BOOST_STATIC_CONSTANT(int, value=0); }; template <> struct traita<int> { BOOST_STATIC_CONSTANT(int, value=1); }; template struct trait1 {}; template <class T> struct trait { BOOST_STATIC_CONSTANT(int, value=traita<T>::value); typedef trait1 t1; }; int main(int argc, char* argv[]) { std::cout << typeid(trait<int>::t1).name() << std::endl << trait<int>::value << std::endl ; return 0; } output:: trait1 1 It would be nice if the first line of output were "trait1", but it isn't. Any assistance would be greatly appreciated. Craig Hicks

Noel Yap

1:40 p.m.

New subject: [Boost-Users] Query regarding the use/limitiations of traits in metaprogramming

--- hicks wrote:

...

Query regarding the use/limitiations of traits in metaprogramming

I am trying to use traits pattern to assist in metaprogramming. I have the following problem.

A traits class "trait" defers a decision to another traits class "trait1" depending on the result of a third traits class "traita". However, the compiler does not cooperate. The code below excutes but gives unexpected output (also shown).

[Note:: The code has been reduced to the minimal to demonstrate the problem. I have a real task at hand not shown here.]

template <class T> struct traita { BOOST_STATIC_CONSTANT(int, value=0); }; template <> struct traita<int> { BOOST_STATIC_CONSTANT(int, value=1); };

template struct trait1 {};

template <class T> struct trait { BOOST_STATIC_CONSTANT(int, value=traita<T>::value); typedef trait1 t1; };

int main(int argc, char* argv[]) { std::cout << typeid(trait<int>::t1).name() << std::endl << trait<int>::value << std::endl ; return 0; }

output::

trait1 1

It would be nice if the first line of output were "trait1", but it isn't.

Any assistance would be greatly appreciated.

I have some questions for you: 1. Why are you so interested in the value of "typeid.name()"? 2. Are you sure this isn't a compiler problem? What compiler(s) have you tried this on? Noel __________________________________________________ Do You Yahoo!? Yahoo! Health - your guide to health and wellness http://health.yahoo.com

hicks

7 May 7 May

2:38 p.m.

New subject: [Boost-Users] Query regarding the use/limitiations of traits in metaprogramming

Hello

...

I have some questions for you: 1. Why are you so interested in the value of "typeid.name()"?

I'm not particulary interested in typeid::name() as an end result. As I said in the letter, I have real task at hand, and condensed the code so that anybody looking at it would be able to get to the point quickly. I used typeid()::name() here as a means of demonstating the problem. The result which is shown by typeid()::name() corresponds to the result encountered in the real task, namely, the next stage of processing is supposed to take place in traits1 but takes place in traits1 instead. In other words, the branching mechanism fails silently.

...

2. Are you sure this isn't a compiler problem? What compiler(s) have you tried this on?

Borland Builder C++ 5. Unfortunately, it's the only one to which I have access now. It could well be a compiler problem. Unless there are some rules which I don't understand. If it is a compiler problem perhaps someone knows of a workaround. I have tried various approaches to no avail. Craig Hicks Noel Yap wrote:

...

--- hicks mailto:hicks@kgk.co.jp wrote:

...
Query regarding the use/limitiations of traits in metaprogramming

I am trying to use traits pattern to assist in metaprogramming. I have the following problem.

A traits class "trait" defers a decision to another traits class "trait1" depending on the result of a third traits class "traita". However, the compiler does not cooperate. The code below excutes but gives unexpected output (also shown).

[Note:: The code has been reduced to the minimal to demonstrate the problem. I have a real task at hand not shown here.]

template <class T> struct traita { BOOST_STATIC_CONSTANT(int, value=0); }; template <> struct traita<int> { BOOST_STATIC_CONSTANT(int, value=1); };

template struct trait1 {};

template <class T> struct trait { BOOST_STATIC_CONSTANT(int, value=traita<T>::value); typedef trait1< ;T, value> t1; };

int main(int argc, char* argv[]) { std::cout << typeid(trait<int>::t1).name() << std::endl << trait<int>::value << std::endl ; return 0; }

output::

trait1 1

It would be nice if the first line of output were "trait1", but it isn't.

Any assistance would be greatly appreciated.

I have some questions for you: 1. Why are you so interested in the value of "typeid.name()"? 2. Are you sure this isn't a compiler problem? What compiler(s) have you tried this on?

Noel

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Noel Yap

4:19 p.m.

New subject: [Boost-Users] Query regarding the use/limitiations of traits in metaprogramming

It looks like it's working find with gcc-2.95.3-5. One thing, though, it gave me a compiler error when I didn't #include <typeinfo>. Since you didn't list which header files you're including, I'm not sure if you're including <typeinfo> or not and what the Borland's behaviour would be if you didn't. Noel --- hicks wrote:

...

Hello

...
I have some questions for you: 1. Why are you so interested in the value of "typeid.name()"?

I'm not particulary interested in typeid::name() as an end result. As I said in the letter, I have real task at hand, and condensed the code so that anybody looking at it would be able to get to the point quickly. I used typeid()::name() here as a means of demonstating the problem. The result which is shown by typeid()::name() corresponds to the result encountered in the real task, namely, the next stage of processing is supposed to take place in traits1 but takes place in traits1 instead. In other words, the branching mechanism fails silently.

...
2. Are you sure this isn't a compiler problem? What compiler(s) have you tried this on?

Borland Builder C++ 5. Unfortunately, it's the only one to which I have access now. It could well be a compiler problem. Unless there are some rules which I don't understand. If it is a compiler problem perhaps someone knows of a workaround. I have tried various approaches to no avail.

Craig Hicks

Noel Yap wrote:

...
--- hicks mailto:hicks@kgk.co.jp wrote:

...
Query regarding the use/limitiations of traits in metaprogramming

I am trying to use traits pattern to assist in metaprogramming. I have the following problem.

A traits class "trait" defers a decision to another traits class "trait1" depending on the result of a third traits class "traita". However, the compiler does not cooperate. The code below excutes but gives unexpected output (also shown).

[Note:: The code has been reduced to the minimal to demonstrate the problem. I have a real task at hand not shown here.]

template <class T> struct traita { BOOST_STATIC_CONSTANT(int, value=0); }; template <> struct traita<int> { BOOST_STATIC_CONSTANT(int, value=1); };

template struct trait1 {};

template <class T> struct trait { BOOST_STATIC_CONSTANT(int, value=traita<T>::value); typedef trait1< ;T, value> t1; };

int main(int argc, char* argv[]) { std::cout << typeid(trait<int>::t1).name() << std::endl << trait<int>::value << std::endl ; return 0; }

output::

trait1 1

It would be nice if the first line of output were "trait1", but it isn't.

Any assistance would be greatly appreciated.

I have some questions for you: 1. Why are you so interested in the value of "typeid.name()"? 2. Are you sure this isn't a compiler problem? What compiler(s) have you tried this on?

Noel

__________________________________________________ Do You Yahoo!? Yahoo! Health - your guide to health and wellness http://health.yahoo.com

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http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl

...

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whastingsnj

8 May 8 May

2:06 a.m.

New subject: Query regarding the use/limitiations of traits in metaprogramming

The following works as desired in CBuilder C++ 6.0: As you have discovered, Borland has a hard time with compile-time constants used in template parameters. #include <typeinfo> #include <iostream> #include "boost/config.hpp" template <class T> struct traita { BOOST_STATIC_CONSTANT(int, value=0); }; template <> struct traita<int> { BOOST_STATIC_CONSTANT(int, value=1); }; template struct trait1 {}; template <class T> struct trait { BOOST_STATIC_CONSTANT(int, value=traita<T>::value); typedef trait1 t1; }; int main(int argc, char* argv[]) { std::cout << typeid(trait<int>::t1).name() << std::endl << trait<int>::value << std::endl ; return 0; }

Raul Huertas Diaz

11:02 a.m.

New subject: [Boost-Users] Query regarding the use/limitiations of traits in metaprogramming

El Tue, 7 May 2002 09:19:31 -0700 (PDT) Noel Yap escribió:

...

It looks like it's working find with gcc-2.95.3-5. One thing, though, it gave me a compiler error when I didn't #include <typeinfo>. Since you didn't list which header files you're including, I'm not sure if you're including <typeinfo> or not and what the Borland's behaviour would be if you didn't.

I tried a different version in gcc 3.0.3 and I think it works find. The modified code is: ________________________________________ int main(int argc, char* argv[]) { std::cout << typeid(trait<int>::t1).name() << std::endl << typeid(trait1).name() << std::endl << typeid(trait1).name() << std::endl << trait<int>::value << std::endl ; return 0; } ________________________________________ and the output is: ________________________________________ 6trait1IiLi1EE 6trait1IiLi1EE 6trait1IiLi0EE 1 ________________________________________ -- Raúl Huertas Díaz Redes y Comunicaciones Ingeniero de Sistemas TCP Sistemas e Ingenieria Fernández Caro, 7, 3ª planta Tel.: +34 91 367 32 79 (Ext. 535) Fax: +34 91 407 71 39 rhuertas@tcpsi.es http://www.tcpsi.es

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hicks
Noel Yap
Peter Dimov
Raul Huertas Diaz
Toon Knapen
whastingsnj