High Performance Dynamic Typing in C++ using a Replacement for boost::any

Christopher Diggins

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9 May 2011CPOL1 min read

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A high-performance alternative to boost::any.

Introduction

The Boost library provides a very useful little class called boost::any which can contain a value of virtually any type as long as that value supports copy construction and assignment. This boost::any type allows dynamic querying of the contained type, and safe type conversions. Despite its usefulness, boost::any is not as efficient as it could be, so I have rewritten my own, which I have immodestly called cdiggins::any.

Updated in 2011: After five years, I have rewritten the class from scratch to fix some really nasty bugs and to simplify the code.

Using cdiggins::any

The cdiggins::any type can be used to hold normal value types, and provides a mechanism to safely and explicitly cast back to the appropriate type.

C++

any a = 42;
cout << a.cast<int>() << endl;
a = 13;
cout << a.cast<int>() << endl;
a = "hello";
cout << a.cast<const char*>() << endl;
a = std::string("1234567890");
cout << a.cast<std::string>() << endl;
int n = 42;
a = &n;
cout << *a.cast<int*>() << endl;
any b = true;
cout << b.cast<bool>() << endl;
swap(a, b);        
cout << a.cast<bool>() << endl;
a.cast<bool>() = false;
cout << a.cast<bool>() << endl;

Design of cdiggins::any

The cdiggins::any class contains two pointers: one to a policy class (any::policy) and one is a pointer to the data (any::data) which may in certain cases be used to contain the data itself (for example, if storing a primitive data type smaller than or equal to the size of a pointer).

The policy class is used for performing allocations, deallocation, copies, etc., and determines whether to use any::data to hold the data or point to the data.

Finally, without further ado, here is the implementation of the cdiggins::any class for your enjoyment:

C++

#pragma once
/*
 * (C) Copyright Christopher Diggins 2005-2011
 * (C) Copyright Pablo Aguilar 2005
 * (C) Copyright Kevlin Henney 2001
 *
 * Distributed under the Boost Software License, Version 1.0. (See
 * accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt
 */

#include <stdexcept>

namespace cdiggins
{
namespace anyimpl
{
    struct bad_any_cast 
    {
    };

    struct empty_any 
    {
    };

    struct base_any_policy 
    {
        virtual void static_delete(void** x) = 0;
        virtual void copy_from_value(void const* src, void** dest) = 0;
        virtual void clone(void* const* src, void** dest) = 0;
        virtual void move(void* const* src, void** dest) = 0;
        virtual void* get_value(void** src) = 0;
        virtual size_t get_size() = 0;
    };

    template<typename T>
    struct typed_base_any_policy : base_any_policy
    {
        virtual size_t get_size() { return sizeof(T); } 
    };

    template<typename T>
    struct small_any_policy : typed_base_any_policy<T>
    {
        virtual void static_delete(void** x) { }
        virtual void copy_from_value(void const* src, void** dest)
            { new(dest) T(*reinterpret_cast<T const*>(src)); }
        virtual void clone(void* const* src, void** dest) { *dest = *src; }
        virtual void move(void* const* src, void** dest) { *dest = *src; }
        virtual void* get_value(void** src) { return reinterpret_cast<void*>(src); }
    };

    template<typename T>
    struct big_any_policy : typed_base_any_policy<T>
    {
        virtual void static_delete(void** x) { if (*x) 
            delete(*reinterpret_cast<T**>(x)); *x = NULL; }
        virtual void copy_from_value(void const* src, void** dest) { 
           *dest = new T(*reinterpret_cast<T const*>(src)); }
        virtual void clone(void* const* src, void** dest) { 
           *dest = new T(**reinterpret_cast<T* const*>(src)); }
        virtual void move(void* const* src, void** dest) { 
          (*reinterpret_cast<T**>(dest))->~T(); 
          **reinterpret_cast<T**>(dest) = **reinterpret_cast<T* const*>(src); }
        virtual void* get_value(void** src) { return *src; }
    };

    template<typename T>
    struct choose_policy 
    {
        typedef big_any_policy<T> type;
    };

    template<typename T> 
    struct choose_policy<T*> 
    { 
        typedef small_any_policy<T*> type; 
    };
    
    struct any;

    /// Choosing the policy for an any type is illegal, but should never happen.
    /// This is designed to throw a compiler error.
    template<>
    struct choose_policy<any>
    {
        typedef void type;
    };

    /// Specializations for small types.
    #define SMALL_POLICY(TYPE) template<> struct 
       choose_policy<TYPE> { typedef small_any_policy<TYPE> type; };

    SMALL_POLICY(signed char);
    SMALL_POLICY(unsigned char);
    SMALL_POLICY(signed short);
    SMALL_POLICY(unsigned short);
    SMALL_POLICY(signed int);
    SMALL_POLICY(unsigned int);
    SMALL_POLICY(signed long);
    SMALL_POLICY(unsigned long);
    SMALL_POLICY(float);
    SMALL_POLICY(bool);

    #undef SMALL_POLICY

    /// This function will return a different policy for each type. 
    template<typename T>
    base_any_policy* get_policy()
    {
        static typename choose_policy<T>::type policy;
        return &policy;
    };
}

struct any
{
private:
    // fields
    anyimpl::base_any_policy* policy;
    void* object;

public:
    /// Initializing constructor.
    template <typename T>
    any(const T& x) 
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) 
    {
        assign(x);
    }       

    /// Empty constructor. 
    any() 
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) 
    { }

    /// Special initializing constructor for string literals. 
    any(const char* x) 
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) 
    { 
        assign(x);
    }

    /// Copy constructor. 
    any(const any& x) 
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL)         
    {            
        assign(x);
    }

    /// Destructor. 
    ~any() {
        policy->static_delete(&object);
    }

    /// Assignment function from another any. 
    any& assign(const any& x) {
        reset();
        policy = x.policy;
        policy->clone(&x.object, &object);
        return *this;
    }

    /// Assignment function. 
    template <typename T>
    any& assign(const T& x) {
        reset();
        policy = anyimpl::get_policy<T>();
        policy->copy_from_value(&x, &object);
        return *this;
    }

    /// Assignment operator.
    template<typename T>
    any& operator=(const T& x) {
        return assign(x);
    }

    /// Assignment operator, specialed for literal strings. 
    /// They have types like const char [6] which don't work as expected. 
    any& operator=(const char* x) {
        return assign(x);
    }

    /// Utility functions
    any& swap(any& x) {
        std::swap(policy, x.policy);
        std::swap(object, x.object);
        return *this;
    }

    /// Cast operator. You can only cast to the original type.
    template<typename T>
    T& cast() {
        if (policy != anyimpl::get_policy<T>()) 
            throw anyimpl::bad_any_cast();
        T* r = reinterpret_cast<T*>(policy->get_value(&object)); 
        return *r;
    }

    /// Returns true if the any contains no value. 
    bool empty() const {
        return policy == anyimpl::get_policy<anyimpl::empty_any>();
    }

    /// Frees any allocated memory, and sets the value to NULL.
    void reset() {
        policy->static_delete(&object);
        policy = anyimpl::get_policy<anyimpl::empty_any>();
    }

    /// Returns true if the two types are the same. 
    bool compatible(const any& x) const {
        return policy == x.policy;
    }
};
}

Final Words

Thanks to Pablo Aguilar who helped with an early version of the cdiggins::any class. Thanks to Raute who helped me identify the critical problems in the original version of cdiggins::any.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By

Christopher Diggins

Software Developer Ara 3D

Canada

I am the designer of the Plato programming language and I am the founder of Ara 3D. I can be reached via email at cdiggins@gmail.com

Comments and Discussions

Code dump of current, for copy & pasters:

David O'Neil30-May-17 10:07

David O'Neil

30-May-17 10:07

Had to look at this this week, and figured I'd code dump it here for anyone who comes afterwards. The following is the code as it currently stands. I believe I have incorporated everything from the below comments.

The code posted in my 'Last version still buggy' no longer blows up in Visual Studio 2015 CE with these changes in place.

For your copy/pasting pleasure:

C++

#pragma once

//CdAny.h:

//-------------------------------------------------------------------------------------------
// The following is derived from Christopher Diggins, Pablo Aguilar, and Kevlin Henney's
// 'any' work available at:
// http://www.codeproject.com/Articles/11250/High-Performance-Dynamic-Typing-in-C-using-a-Repla.
//
// Their original copyright notice is as follows:
// * (C) Copyright Christopher Diggins 2005
// * (C) Copyright Pablo Aguilar 2005
// * (C) Copyright Kevlin Henney 2001
// *
// * Distributed under the Boost Software License, Version 1.0. (See
// * accompanying file LICENSE_1_0.txt or copy at
// * http://www.boost.org/LICENSE_1_0.txt)
//
// The changes made to this code include the ones listed in the comments at the previous
// CodeProject article, and tossing it into the 'cd' namespace, as well as replacement of the
// 'bad_any_cast' with my own Exception. The last one will need to be undone for anyone
// who copy/pastes this into their code, and you may want to change the namespace as well - up
// to you.
// Thanks Christopher, Pablo, and Kevlin for making this available, and the other contributors
// for their bug fixes.
//-------------------------------------------------------------------------------------------

//namespace cdiggins
namespace cd {   //For 'Christopher Diggins', for easier typing

   namespace anyimpl {

      struct empty_any {
         };

      struct base_any_policy {

         virtual void static_delete(void** x) = 0;

         virtual void copy_from_value(void const* src, void** dest) = 0;

         virtual void clone(void* const* src, void** dest) = 0;

         virtual void move(void* const* src, void** dest) = 0;

         virtual void* get_value(void** src) = 0;

         virtual void* get_value(void* const * src) const = 0;

         virtual size_t get_size() = 0;

         };

      template<typename T>
      struct typed_base_any_policy : base_any_policy {
         virtual size_t get_size() { return sizeof(T); } 
         };

      template<typename T>
      struct small_any_policy : typed_base_any_policy<T> {

         virtual void static_delete(void** x) override { }

         virtual void copy_from_value(void const* src, void** dest) {
            //This used to be:
            //new(dest) T(*reinterpret_cast<T const*>(src)); 
            //But this is the small_any_policy, and ints and other small objects
            //shouldn't need to be pointed to by an object.  So a simple 'clone',
            //or move will suffice, so use the same code as them:
            //*dest = const_cast<void*>(src);
            //In this case, we are really receiving the address of the the 'object' variable
             *dest = *(reinterpret_cast<void**>((const_cast<void*>(src))));
            }

         virtual void clone(void* const* src, void** dest) { *dest = *src; }

         virtual void move(void* const* src, void** dest) { *dest = *src; }

         virtual void* get_value(void** src) { return reinterpret_cast<void*>(src); }

         void* get_value(void* const * src) const override {
            return reinterpret_cast<void*>(const_cast<void**>(src));
            }

         };

      template<typename T>
      struct big_any_policy : typed_base_any_policy<T> {
         virtual void static_delete(void** x) override {
            if (*x) 
               delete(*reinterpret_cast<T**>(x));
            *x = NULL;
            }

         virtual void copy_from_value(void const* src, void** dest) { 
            *dest = new T(*reinterpret_cast<T const*>(src));
            }

         virtual void clone(void* const* src, void** dest) { 
            *dest = new T(**reinterpret_cast<T* const*>(src));
            }

         virtual void move(void* const* src, void** dest) { 
           (*reinterpret_cast<T**>(dest))->~T(); 
           **reinterpret_cast<T**>(dest) = **reinterpret_cast<T* const*>(src);
           }

         virtual void* get_value(void** src) { return *src; }

         void* get_value(void* const * src) const override { return *const_cast<void**>(src); }

      };

      template<typename T>
      struct choose_policy {
         typedef big_any_policy<T> type;
         };

      template<typename T> 
      struct choose_policy<T*> { 
         typedef small_any_policy<T*> type; 
         };

      struct any; //Forward declaration

      /// Choosing the policy for an any type is illegal, but should never happen.
      /// This is designed to throw a compiler error.
      template<>
      struct choose_policy<any> {
         typedef void type;
         };

      /// Specializations for small types.
      #define SMALL_POLICY(TYPE) template<> struct choose_policy<TYPE> { \
                  typedef small_any_policy<TYPE> type; };

      SMALL_POLICY(signed char);
      SMALL_POLICY(unsigned char);
      SMALL_POLICY(signed short);
      SMALL_POLICY(unsigned short);
      SMALL_POLICY(signed int);
      SMALL_POLICY(unsigned int);
      SMALL_POLICY(signed long);
      SMALL_POLICY(unsigned long);
      SMALL_POLICY(float);
      SMALL_POLICY(bool);

      #undef SMALL_POLICY

      /// This function will return a different policy for each type. 
      template<typename T>
      base_any_policy* get_policy() {
         static typename choose_policy<T>::type policy;
         return &policy;
         };

      }  //End of anyimpl namespace

      struct any {
         private:
            // fields
            anyimpl::base_any_policy* policy;
            void* object;

         public:
            /// Initializing constructor.
            template <typename T>
            //This used to be:
            //any(const T& x) : policy(anyimpl::get_policy<anyimpl::empty_any>()),
            //          object(NULL) {
            //I am changing it to force the initial construction to use the small_policy:
            any(const T& x) : policy(anyimpl::get_policy<unsigned int>()), object(NULL) {
               assign(x);
               }      

            /// Empty constructor. 
            //This used to be:
            //any() : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) {
            //But why should an empty 'any' receive a default 'big_any_policy'???
            //This starts calling 'new' and 'delete' under the hood.
            //So let's try the following to force a small_policy:
            any() : policy(anyimpl::get_policy<unsigned int>()), object(NULL) {
               }

            /// Special initializing constructor for string literals. 
            any(const char* x) : policy(anyimpl::get_policy<anyimpl::empty_any>()), 
                        object(NULL) {

               assign(x);
               }

            /// Copy constructor. 
            any(const any& x) : policy(anyimpl::get_policy<anyimpl::empty_any>()),
                        object(NULL) {

               assign(x);
               }

            /// Destructor. 
            ~any() {
               policy->static_delete(&object);
               }

            /// Assignment function from another any. 
            any& assign(const any& x) {
               reset();
               policy = x.policy;
               policy->clone(&x.object, &object);
               return *this;
               }

            /// Assignment function. 
            template <typename T>
            any& assign(const T& x) {
               reset();
               policy = anyimpl::get_policy<T>();
               policy->copy_from_value(&x, &object);
               return *this;
               }

            /// Assignment operator.
            template<typename T>
            any& operator=(const T& x) {
               return assign(x);
               }

            any& operator=(const any & x) {
               //Was:
               //policy = x.policy;
               //policy->copy_from_value(&x.object, &object);
               //return *this;
               //reset();
               return assign(x);
               }

            any& operator()(const any & x) {
               policy = x.policy;
               policy->copy_from_value(&x.object, &object);
               return *this;
               }

            /// Assignment operator, specialed for literal strings. 
            /// They have types like const char [6] which don't work as expected. 
            any& operator=(const char* x) {
               return assign(x);
               }

            /// Utility functions
            any& swap(any& x) {
               std::swap(policy, x.policy);
               std::swap(object, x.object);
               return *this;
               }

            /// Cast operator. You can only cast to the original type.
            template<typename T>
            T& cast() {
               if (policy != anyimpl::get_policy<T>()) {
                  // the following was 'throw anyimpl::bad_any_cast();'
                  throw dwl::Exception(_T("Bad 'any' cast"));
                  }

               T* r = reinterpret_cast<T*>(policy->get_value(&object)); 
               return *r;
               }

            /// Returns true if the any contains no value. 
            bool empty() const {
               return policy == anyimpl::get_policy<anyimpl::empty_any>();
               }

            /// Frees any allocated memory, and sets the value to NULL.
            void reset() {
               policy->static_delete(&object);
               //The following used to be:
               //policy = anyimpl::get_policy<anyimpl::empty_any>();
               //But why should the policy default to the big_any_policy?  Therefore,:
               policy = anyimpl::get_policy<unsigned int>();
               }

            /// Returns true if the two types are the same. 
            template<typename T>
            bool isA() {
               return policy == anyimpl::get_policy<T>();
               }

             template <typename T> operator T&() { return cast<T>(); }
             template <typename T> operator T&() const { return cast<T>(); }

             template<typename T>
             T& cast() const {
                 if (policy != anyimpl::get_policy<T>()) {
                  throw dwl::Exception(_T("Bad 'any' cast"));
                  //was:
                  //throw anyimpl::bad_any_cast();
                    }
                 T* r = reinterpret_cast<T*>(policy->get_value(&object));
                 return *r;
                }

         }; //End of 'any' struct definition

   }

Sudden Sun Death Syndrome (SSDS) is a very real concern which we should be raising awareness of. 156 billion suns die every year before they're just 1 billion years old.
While the military are doing their part, it simply isn't enough to make the amount of nukes needed to save those poor stars. - TWI2T3D (Reddit)

Implicit cast fix

Member 1154432525-Mar-15 11:59

Member 11544325

25-Mar-15 11:59

If you want implicit casting so heavy use does not muck up your sweet, sweet code, you will pretty quickly find that you get a compile error when attempting to use const any&.

The fix is as follows:

in base_any_policy, add

C++

virtual void* get_value(void* const * src) const = 0;

in small_any_policy, add

C++

void* get_value(void* const * src) const override { return reinterpret_cast<void*>(const_cast<void**>(src)); }

in big_any_policy, add

C++

void* get_value(void* const * src) const override { return *const_cast<void**>(src); }

in struct any, add

C++

template <typename T> operator T&() { return cast<T>(); }
template <typename T> operator T&() const { return cast<T>(); }

template<typename T>
T& cast() const
{
    if (policy != anyimpl::get_policy<T>())
    {
        throw anyimpl::bad_any_cast();
    }
    T* r = reinterpret_cast<T*>(policy->get_value(&object));
    return *r;
}

Note these changes were applied to the code found in the "Fix the const problem" post.

modified 25-Mar-15 18:18pm.

Last version still buggy (but I don't have a solution)

David O'Neil4-Oct-14 11:45

David O'Neil

4-Oct-14 11:45

Perform the following:

C++

#include "CdAny.h"   //Latest version

class Junk {
   private:
      int i;   //Just for some size
      int j;
   };

int main() {
   Junk junk;
   Junk * junkPtr = &junk;

   cd::any orig(junkPtr);
   cd::any second;
   second = orig;
   second = orig;  //Blows up here.

   return 0;
   }

As I said, I don't have a solution other than not to use such a construct. But the fact that it fails indicates there may be other failure modes that still need addressed, so keep an eye out for them.

My CodeProject Articles :: Our forgotten astronomic heritage :: My website.

Please someone add Move constructor

jeefo124-May-14 16:54

jeefo12

4-May-14 16:54

Hi all, I want to add move constructor and Assignment move operator.
I tried

any(any&& x)
            : policy(x.policy), object(x.object)
        {
            x.policy = nullptr;
            x.object = nullptr;
        }

But it doesn't work Frown | :(

any help ?

not working with "unsigned int"

cristi.arghiroiu19-Feb-14 1:00

cristi.arghiroiu

19-Feb-14 1:00

First, thanks for the class.
I needed it as convenience in some logging class to help in debugging.
I've tried the last version, the one integrated by @pj220_2006 and the following failed:

C++

cdiggins::any st;
assert( st.empty() );

I've solved the issue by dropping the unsigned int fix and putting back in place the initialization with anyimpl::empty_any.
The key fix is that now empty_any has a specialization with small_any_policy instead of the default one, which would use big_any_policy.

Delta's are:
- in implementation namespace:

C++

template<>
struct choose_policy< empty_any > { typedef small_any_policy< empty_any > type; };

- in any class:

C++

/// Initializing constructor.
template <typename T>
any(const T& x)
    : policy( anyimpl::get_policy< anyimpl::empty_any >() ) , object( nullptr )
{
  assign(x);
}

/// Empty constructor.
any()
    : policy( anyimpl::get_policy< anyimpl::empty_any >() ) , object( nullptr )
{
}

// ...

/// Frees any allocated memory, and sets the value to nullptr.
void reset()
{
  policy->static_delete(&object);
  policy = anyimpl::get_policy< anyimpl::empty_any >();
}

fix the const problem

pj220_20068-Aug-13 22:12

pj220_2006

8-Aug-13 22:12

if T has const prefix, some error will be occour. i also check the David's isA template , when T is a type with const prefix for example ( const char), a error is occour.because the variable temp must be initialized. in order to fix const problem, i add help template class ( remove_const ) to remove the const prefix to solve it. i also chenge David's IsA function to avoid using the temp variable.

C++

//-------------------------------------------------------------------------------------------
// The following is derived from Christopher Diggins, Pablo Aguilar, and Kevlin Henney's
// 'any' work available at:
// http://www.codeproject.com/Articles/11250/High-Performance-Dynamic-Typing-in-C-using-a-Repla.
//
// Their original copyright notice is as follows:
// * (C) Copyright Christopher Diggins 2005
// * (C) Copyright Pablo Aguilar 2005
// * (C) Copyright Kevlin Henney 2001
// *
// * Distributed under the Boost Software License, Version 1.0. (See
// * accompanying file LICENSE_1_0.txt or copy at
// * http://www.boost.org/LICENSE_1_0.txt)
//
// The only three changes I have made is 1) to toss it into the 'DWL' namespace (as I
// don't like typing more than I have to, and those extra four letters add up, especially
// as I use it in function signatures), 2) replacement of the 'bad_any_cast' derived from
// std::bad_cast with a DwlException, and 3) added the templated 'isA' function to
// make testing for type much easier.  Of course, the seccond change makes 'catching'
// just this type of error much harder if you wish to do so, but you may change to your
// heart's content for your own projects since you have the code.
// Thanks Christopher, Pablo, and Kevlin for making this available.
//
// Oops - I forgot about the changes listed above in my preface to this code.
//-------------------------------------------------------------------------------------------

#ifndef RMW_CDIGGINS_ANY_HPP
#define RMW_CDIGGINS_ANY_HPP

//#pragma once
/*
 * (C) Copyright Christopher Diggins 2005-2011
 * (C) Copyright Pablo Aguilar 2005
 * (C) Copyright Kevlin Henney 2001
 *
 * Distributed under the Boost Software License, Version 1.0. (See
 * accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt
 */

#include <stdexcept>

namespace dwl 
{
	namespace anyimpl 
	{
		struct bad_any_cast 
		{
		};

		struct empty_any 
		{
		};

		struct base_any_policy
		{

			virtual void static_delete( void** x) = 0;

			virtual void copy_from_value(void const* src, void** dest) = 0;

			virtual void clone(void* const* src, void** dest) = 0;

			virtual void move(void* const* src, void** dest) = 0;

			virtual void* get_value(void** src) = 0;

			virtual size_t get_size() = 0;

		};

		template<typename T>
		struct typed_base_any_policy : base_any_policy 
		{
			virtual size_t get_size() { return sizeof(T); } 
		};

		template<typename T>
		struct small_any_policy : typed_base_any_policy<T> 
		{

			virtual void static_delete(void** x) { }

			virtual void copy_from_value(void const* src, void** dest) 
			{
				//This used to be:
				//new(dest) T(*reinterpret_cast<T const*>(src)); 
				//But this is the small_any_policy, and ints and other small objects
				//shouldn't need to be pointed to by an object.
				//In this case, we are really receiving the address of the the 'object' variable
				*dest = *(reinterpret_cast<void**>((const_cast<void*>(src))));
			}

			virtual void clone(void* const* src, void** dest) { *dest = *src; }

			virtual void move(void* const* src, void** dest) { *dest = *src; }

			virtual void* get_value(void** src) { return reinterpret_cast<void*>(src); }

		};

		template<typename T>
		struct remove_const 
		{
			typedef T type;
		};

		template<typename T> 
		struct remove_const<const T>
		{ 
			typedef T type; 
		};

		template<typename T>
		struct big_any_policy : typed_base_any_policy<T> 
		{
			virtual void static_delete( void** x) 
			{
				if (*x) 
				{
					delete (*reinterpret_cast< remove_const<T>::type**>(x));
				}
				*x = NULL;
			}

			virtual void copy_from_value(void const* src, void** dest) 
			{ 
				*dest = new remove_const<T>::type(*reinterpret_cast<T const*>(src));
			}

			virtual void clone(void* const* src, void** dest)
			{ 
				*dest = new remove_const<T>::type(**reinterpret_cast<T* const*>(src));
			}

			virtual void move(void* const* src, void** dest) 
			{ 
				(*reinterpret_cast<remove_const<T>::type**>(dest))->~T(); 
				**reinterpret_cast<remove_const<T>::type**>(dest) = **reinterpret_cast<T* const*>(src);
			}

			virtual void* get_value(void** src) { return *src; }
		};

		template<typename T>
		struct choose_policy 
		{
			typedef big_any_policy<T> type;
		};

		template<typename T> 
		struct choose_policy<T*>
		{ 
			typedef small_any_policy<T*> type; 
		};

		struct any; //Forward declaration

		/// Choosing the policy for an any type is illegal, but should never happen.
		/// This is designed to throw a compiler error.
		template<>
		struct choose_policy<any> 
		{
			typedef void type;
		};

		/// Specializations for small types.
#define SMALL_POLICY(TYPE) template<> struct choose_policy<TYPE> { typedef small_any_policy<TYPE> type; };
		SMALL_POLICY(signed char);
		SMALL_POLICY(unsigned char);
		SMALL_POLICY(signed short);
		SMALL_POLICY(unsigned short);
		SMALL_POLICY(signed int);
		SMALL_POLICY(unsigned int);
		SMALL_POLICY(signed long);
		SMALL_POLICY(unsigned long);
		SMALL_POLICY(float);
		SMALL_POLICY(bool);
		SMALL_POLICY(const signed char);
		SMALL_POLICY(const unsigned char);
		SMALL_POLICY(const signed short);
		SMALL_POLICY(const unsigned short);
		SMALL_POLICY(const signed int);
		SMALL_POLICY(const unsigned int);
		SMALL_POLICY(const signed long);
		SMALL_POLICY(const unsigned long);
		SMALL_POLICY(const float);
		SMALL_POLICY(const bool);
#undef SMALL_POLICY

		/// This function will return a different policy for each type. 
		template<typename T>
		base_any_policy* get_policy() 
		{
			static typename choose_policy<T>::type policy;
			return &policy;
		};

	}  //End of anyimpl namespace

	struct any 
	{
	private:
		// fields
		anyimpl::base_any_policy* policy;
		void* object;

	public:
		/// Initializing constructor.
		template <typename T>
		//This used to be:
		//any(const T& x) : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) {
		//I am changing it to force the initial construction to use the small_policy:
		any(const T& x) : policy(anyimpl::get_policy<unsigned int>()), object(NULL) 
		{
			assign(x);
		}      

		/// Empty constructor. 
		//This used to be:
		//any() : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) {
		//But why should an empty 'any' receive a default 'big_any_policy'???
		//This starts calling 'new' and 'delete' under the hood.
		//So let's try the following to force a small_policy:
		any() : policy(anyimpl::get_policy<unsigned int>()), object(NULL) 
		{
		}

		/// Special initializing constructor for string literals. 
		any(const char* x) : policy(anyimpl::get_policy<anyimpl::empty_any>()), 
			object(NULL) 
		{
				assign(x);
		}

		/// Copy constructor. 
		any(const any& x) : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) 
		{
			assign(x);
		}

		/// Destructor. 
		~any() 
		{
			policy->static_delete(&object);
		}

		/// Assignment function from another any. 
		any& assign(const any& x) 
		{
			reset();
			policy = x.policy;
			policy->clone(&x.object, &object);
			return *this;
		}

		/// Assignment function. 
		template <typename T>
		any& assign(const T& x)
		{
			reset();
			policy = anyimpl::get_policy<T>();
			policy->copy_from_value(&x, &object);
			return *this;
		}

		/// Assignment operator.
		template<typename T>
		any& operator=(const T& x) 
		{
			return assign(x);
		}

		any& operator=(const any & x)
		{
			/*policy = x.policy;
			policy->copy_from_value(&x.object, &object);
			return *this;*/
			reset();
			return assign(x);
		}

		any& operator()(const any & x) 
		{
			policy = x.policy;
			policy->copy_from_value(&x.object, &object);
			return *this;
		}

		/// Assignment operator, specialed for literal strings. 
		/// They have types like const char [6] which don't work as expected. 
		any& operator=(const char* x) 
		{
			return assign(x);
		}

		/// Utility functions
		any& swap(any& x) 
		{
			std::swap(policy, x.policy);
			std::swap(object, x.object);
			return *this;
		}

		/// Cast operator. You can only cast to the original type.
		template<typename T>
		T& cast() 
		{
			if (policy != anyimpl::get_policy<T>()) 
			{
				throw anyimpl::bad_any_cast();
			}
			T* r = reinterpret_cast<T*>(policy->get_value(&object)); 
			return *r;
		}

		/// Returns true if the any contains no value. 
		bool empty() const 
		{
			return policy == anyimpl::get_policy<anyimpl::empty_any>();
		}

		/// Frees any allocated memory, and sets the value to NULL.
		void reset() 
		{
			policy->static_delete(&object);
			//The following used to be:
			//policy = anyimpl::get_policy<anyimpl::empty_any>();
			//But why should the policy default to the big_any_policy?  Therefore,:
			policy = anyimpl::get_policy<unsigned int>();
		}

		/// Returns true if the two types are the same. 
		bool isA(const any& x) const 
		{
			return policy == x.policy;
		}

		template<typename T>
		bool isA() 
		{
			return policy == anyimpl::get_policy<T>();
		}

	}; //End of 'any' struct definition
}

#endif

modified 9-Aug-13 4:51am.

Re: fix the const problem

skyformat99@gmail.com31-Jan-14 21:47

skyformat99@gmail.com

31-Jan-14 21:47

very good

Re: fix the const problem

David O'Neil28-Feb-14 20:23

David O'Neil

28-Feb-14 20:23

Cool!

My website :: My book revealing the forgotten astronomy of our ancestors.

Re: fix the const problem

Martial Spirit19-Mar-16 18:26

Martial Spirit

19-Mar-16 18:26

cannot through gcc compiler.

Best Regards

Bugfix

David O'Neil9-Jul-13 20:45

David O'Neil

9-Jul-13 20:45

It has been a while, but I finally got around to looking at the issue more deeply. The problem I mentioned in my previous message only cropped up in semi-complicated circumstances, and with constructs evidently not used by anyone else who has used your class. The base problem appears to be that your empty constructor, although it defaults to empty_any, under the hood is defaulting the the big_any_policy which is calling new and delete. That becomes a big problem when the any object changes to holding a different type via copy construction, or operator=().

That issue came up intermittently in my code - sometimes I didn't get an error, other times I did. The trigger seemed to be that often I used 'any' objects in classes which were held in vectors, or other containers, and a lot of copy construction was occurring.

Therefore I had to modify your empty constructors to default to signed int construction, to make them default to small_any_policy. I also modified copy constructors, and created a couple others in order to address all of my usage cases. Another change I just saw is in the copy_from_value routine for the small_any_policy, as commented below. The following isn't guaranteed to be bug-free, but using it no longer results in undefined behavior bug crashes in my program. Feel free to modify it back into your original class, as I've wrapped it in my own namespace for typing convenience on my end.

If you, or anyone sees anything I've missed, please holler. And thank you for your work on this, and making it freely available! It taught me a lot, and is used extensively in my code.

David

C++

//-------------------------------------------------------------------------------------------
// The following is derived from Christopher Diggins, Pablo Aguilar, and Kevlin Henney's
// 'any' work available at:
// http://www.codeproject.com/Articles/11250/High-Performance-Dynamic-Typing-in-C-using-a-Repla.
//
// Their original copyright notice is as follows:
// * (C) Copyright Christopher Diggins 2005
// * (C) Copyright Pablo Aguilar 2005
// * (C) Copyright Kevlin Henney 2001
// *
// * Distributed under the Boost Software License, Version 1.0. (See
// * accompanying file LICENSE_1_0.txt or copy at
// * http://www.boost.org/LICENSE_1_0.txt)
//
// The only three changes I have made is 1) to toss it into the 'DWL' namespace (as I
// don't like typing more than I have to, and those extra four letters add up, especially
// as I use it in function signatures), 2) replacement of the 'bad_any_cast' derived from
// std::bad_cast with a DwlException, and 3) added the templated 'isA' function to
// make testing for type much easier.  Of course, the seccond change makes 'catching'
// just this type of error much harder if you wish to do so, but you may change to your
// heart's content for your own projects since you have the code.
// Thanks Christopher, Pablo, and Kevlin for making this available.
//
// Oops - I forgot about the changes listed above in my preface to this code.
//-------------------------------------------------------------------------------------------

#ifndef RMW_CDIGGINS_ANY_HPP
#define RMW_CDIGGINS_ANY_HPP


//#pragma once
/*
 * (C) Copyright Christopher Diggins 2005-2011
 * (C) Copyright Pablo Aguilar 2005
 * (C) Copyright Kevlin Henney 2001
 *
 * Distributed under the Boost Software License, Version 1.0. (See
 * accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt
 */

#include <stdexcept>


//namespace cdiggins
namespace dwl {
   namespace anyimpl {

      struct empty_any {
         };

      struct base_any_policy {
      
         virtual void static_delete(void** x) = 0;
         
         virtual void copy_from_value(void const* src, void** dest) = 0;
         
         virtual void clone(void* const* src, void** dest) = 0;
         
         virtual void move(void* const* src, void** dest) = 0;
         
         virtual void* get_value(void** src) = 0;
         
         virtual size_t get_size() = 0;
         
         };

      template<typename T>
      struct typed_base_any_policy : base_any_policy {
         virtual size_t get_size() { return sizeof(T); } 
         };

      template<typename T>
      struct small_any_policy : typed_base_any_policy<T> {
      
         virtual void static_delete(void** x) { }
         
         virtual void copy_from_value(void const* src, void** dest) {
            //This used to be:
            //new(dest) T(*reinterpret_cast<T const*>(src)); 
            //But this is the small_any_policy, and ints and other small objects
            //shouldn't need to be pointed to by an object.
            //In this case, we are really receiving the address of the the 'object' variable
             *dest = *(reinterpret_cast<void**>((const_cast<void*>(src))));
            }
            
         virtual void clone(void* const* src, void** dest) { *dest = *src; }
         
         virtual void move(void* const* src, void** dest) { *dest = *src; }
         
         virtual void* get_value(void** src) { return reinterpret_cast<void*>(src); }
         
         };

      template<typename T>
      struct big_any_policy : typed_base_any_policy<T> {
         virtual void static_delete(void** x) {
            if (*x) 
               delete(*reinterpret_cast<T**>(x));
            *x = NULL;
            }
            
         virtual void copy_from_value(void const* src, void** dest) { 
            *dest = new T(*reinterpret_cast<T const*>(src));
            }
            
         virtual void clone(void* const* src, void** dest) { 
            *dest = new T(**reinterpret_cast<T* const*>(src));
            }
            
         virtual void move(void* const* src, void** dest) { 
           (*reinterpret_cast<T**>(dest))->~T(); 
           **reinterpret_cast<T**>(dest) = **reinterpret_cast<T* const*>(src);
           }
           
         virtual void* get_value(void** src) { return *src; }
         
      };

      template<typename T>
      struct choose_policy {
         typedef big_any_policy<T> type;
         };

      template<typename T> 
      struct choose_policy<T*> { 
         typedef small_any_policy<T*> type; 
         };
      
      struct any; //Forward declaration

      /// Choosing the policy for an any type is illegal, but should never happen.
      /// This is designed to throw a compiler error.
      template<>
      struct choose_policy<any> {
         typedef void type;
         };

      /// Specializations for small types.
      #define SMALL_POLICY(TYPE) template<> struct choose_policy<TYPE> { typedef small_any_policy<TYPE> type; };

      SMALL_POLICY(signed char);
      SMALL_POLICY(unsigned char);
      SMALL_POLICY(signed short);
      SMALL_POLICY(unsigned short);
      SMALL_POLICY(signed int);
      SMALL_POLICY(unsigned int);
      SMALL_POLICY(signed long);
      SMALL_POLICY(unsigned long);
      SMALL_POLICY(float);
      SMALL_POLICY(bool);

      #undef SMALL_POLICY

      /// This function will return a different policy for each type. 
      template<typename T>
      base_any_policy* get_policy() {
         static typename choose_policy<T>::type policy;
         return &policy;
         };
                  
      }  //End of anyimpl namespace



      struct any {
         private:
            // fields
            anyimpl::base_any_policy* policy;
            void* object;

         public:
            /// Initializing constructor.
            template <typename T>
            //This used to be:
            //any(const T& x) : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) {
            //I am changing it to force the initial construction to use the small_policy:
            any(const T& x) : policy(anyimpl::get_policy<unsigned int>()), object(NULL) {
               assign(x);
               }      

            /// Empty constructor. 
            //This used to be:
            //any() : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) {
            //But why should an empty 'any' receive a default 'big_any_policy'???
            //This starts calling 'new' and 'delete' under the hood.
            //So let's try the following to force a small_policy:
            any() : policy(anyimpl::get_policy<unsigned int>()), object(NULL) {
               }

            /// Special initializing constructor for string literals. 
            any(const char* x) : policy(anyimpl::get_policy<anyimpl::empty_any>()), 
                        object(NULL) {
                        
               assign(x);
               }

            /// Copy constructor. 
            any(const any& x) : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL) {
               assign(x);
               }

            /// Destructor. 
            ~any() {
               policy->static_delete(&object);
               }

            /// Assignment function from another any. 
            any& assign(const any& x) {
               reset();
               policy = x.policy;
               policy->clone(&x.object, &object);
               return *this;
               }

            /// Assignment function. 
            template <typename T>
            any& assign(const T& x) {
               reset();
               policy = anyimpl::get_policy<T>();
               policy->copy_from_value(&x, &object);
               return *this;
               }

            /// Assignment operator.
            template<typename T>
            any& operator=(const T& x) {
               return assign(x);
               }

            any& operator=(const any & x) {
               /*policy = x.policy;
               policy->copy_from_value(&x.object, &object);
               return *this;*/
               reset();
               return assign(x);
               }
               
            any& operator()(const any & x) {
               policy = x.policy;
               policy->copy_from_value(&x.object, &object);
               return *this;
               }

            /// Assignment operator, specialed for literal strings. 
            /// They have types like const char [6] which don't work as expected. 
            any& operator=(const char* x) {
               return assign(x);
               }

            /// Utility functions
            any& swap(any& x) {
               std::swap(policy, x.policy);
               std::swap(object, x.object);
               return *this;
               }
               
            /// Cast operator. You can only cast to the original type.
            template<typename T>
            T& cast() {
               if (policy != anyimpl::get_policy<T>()) 
                  throw DwlException(_T("Bad 'any' cast"));// was throw anyimpl::bad_any_cast();
               T* r = reinterpret_cast<T*>(policy->get_value(&object)); 
               return *r;
               }

            /// Returns true if the any contains no value. 
            bool empty() const {
               return policy == anyimpl::get_policy<anyimpl::empty_any>();
               }

            /// Frees any allocated memory, and sets the value to NULL.
            void reset() {
               policy->static_delete(&object);
               //The following used to be:
               //policy = anyimpl::get_policy<anyimpl::empty_any>();
               //But why should the policy default to the big_any_policy?  Therefore,:
               policy = anyimpl::get_policy<unsigned int>();
               }

            /// Returns true if the two types are the same. 
            bool isA(const any& x) const {
               return policy == x.policy;
               }
            
            template<typename T>
            bool isA() {
               T temp;
               return isA(temp);
               }
         }; //End of 'any' struct definition
   }

#endif // RMW_CDIGGINS_ANY_HPP

My website :: My book revealing the forgotten astronomy of our ancestors.

modified 15-Jul-13 17:35pm.

An overlooked usage case in new code

David O'Neil26-Jan-13 19:01

David O'Neil

26-Jan-13 19:01

Ported my project to the new code and it went into never-never land. After painful debugging, found it occurred after the following scenario:

Have a control which has an 'any' as a user variable. It is defaulted to nothing. Later, that is assigned to a pointer for a class. And even later it gets reassigned to another pointer to a class. The reassignments occur through the '=' operator.

The program was crashing after the first 'pointer-to-pointer' reassignment took place (not the initial assignment to a pointer). Evidently your SMALL_POLICY settings are not occurring for the new reassignments, and the 'delete' operator is being called on a pointer.

I thought about creating a template function like "any::setToPointer([pointer type])", but instead got around it by using the following construct:

SomeClass * p = &something;
any tempSomething(p);
anotherClassAny = tempSomething;

This has fixed the issue, and my program is working again. Not the cleanest syntax. Hope this helps others. If you change the code to fix this, please let me know. Thanks!

My website :: My book revealing the forgotten astronomy of our ancestors.

A small helper function for you

David O'Neil24-Jan-13 17:53

David O'Neil

24-Jan-13 17:53

I just updated my projects to use your new code. First, congratulations on the changes - this updated version is SO much cleaner than the original I can almost wrap my head around it! But I was missing the 'type' function of your old version, as my main project using this tested against that. So I came up with the following small addition which makes replacing that functionality much easier.

template<typename T>
bool compatible() {
  T temp;
  return compatible(temp);
  }

Just add this under the definition of the other 'compatible' function. For those readers who try to use it and are unfamiliar with the template terminology, an example invocation would be something like

if (!buttonC->user.compatible<int>()) doSomething();

Pretty simple, and not much of an addition, but hopefully helpful to some.

[Edit] Having used this for an hour, I'm changing 'compatible' to 'isA', as it better describes the usage context. For example,

if (!buttonC->user.isA<int>()) doSomething();

is a richer and more meaningful syntax than the original.

My website :: My book revealing the forgotten astronomy of our ancestors.

modified 25-Jan-13 1:32am.

error: 'TYPE' was not declared in this scope

yurenjimi198520-Nov-12 15:44

yurenjimi1985

20-Nov-12 15:44

XML

/// Specializations for small types.
    #define SMALL_POLICY(TYPE) template<> struct
       choose_policy<TYPE> { typedef small_any_policy<TYPE> type; };

94:22: error: 'TYPE' was not declared in this scope

What is the TYPE ?? I am using g++ to compile it.

Re: error: 'TYPE' was not declared in this scope

Member 968039912-Dec-12 12:10

Member 9680399

12-Dec-12 12:10

Get rid of the line break and it should build:

XML

#define SMALL_POLICY(TYPE) template<> struct choose_policy<TYPE> { typedef small_any_policy<TYPE> type; };

It looks good, but is that dynamic typing?

Jamming114-May-11 12:20

Jamming1

14-May-11 12:20

Hi there, correct me if I'm wrong: my understanding of dynamic typing goes like this:
using the sample code in your article, I would like to do the following:

any a = 42; //here the type is int
    //in dynamic typing, I don't have to do any cast like you did:
//cout << a.cast<int>() << endl;<br />
    //But the compiler (if "any" class has been written carefully) should figure out <br />
    // the type of the data as int and do the appropriate int cast like this:
cout << a << endl;
a = 13;
//cout << a.cast<int>() << endl;
cout << a << endl;
a = "hello";
    //Now the type is char* , so again, in dynamic typed languages (as in <br />
    //JavaScript for example), all I have to do is this:
    cout << a << endl;
    //And not this:
//cout << a.cast<const char*>() << endl;
a = std::string("1234567890");
cout << a.cast<std::string>().c_str() << endl;
int n = 42;
a = &n;
cout << *a.cast<int*>() << endl;
any b = true;
cout << b.cast<bool>() << endl;
swap(a, b);
cout << a.cast<bool>() << endl;
a.cast<bool>() = false;
cout << a.cast<bool>() << endl;
    return 0;

What I'm saying is that the class as is can do conversion if there is an assignment operator, but in general, if the context of using the "any" variable is ambiguous, the compiler does not really know how to convert the type. In your example, because "<<" operator for cout is overloaded, then, the explicit call to cast() is necessary to tell the compiler which overload to use. However, this is not what I think of dynamic typing. I don't have to do explicit casts to tell the compiler the actual type of "any".
Is there any way that I can modify the class so that I don't have to do explicit casts?

Re: It looks good, but is that dynamic typing?

MetaVoid29-Sep-11 9:46

MetaVoid

29-Sep-11 9:46

I agree. It is very clever made,but the syntax is very ugly.
Also, I tried to use in a real project as a generic datasource, but since
it has no info on the actual type it holds, using it as a return type was not
very nice.
Also, it did not handle simple stuff like

any v1=12;
int num=v1;

I though it would be like the Variant type in VB or Delphi, but perhaps this
is not the goal and speed is.

Re: It looks good, but is that dynamic typing?

jcmalek30-Jan-15 5:49

jcmalek

30-Jan-15 5:49

You could do something a little closer to what you are both looking for by overloading the casting operator in the any class:

template<typename T>
operator T&() {
    return cast<T>();
}

This would let you do things like:

cdiggins::any a = 5;
int b = a;

Or:

void my_function(int b) {
}
cdiggins::any a = 5;
my_function(a);

without having to explicitly cast anything.

This takes advantage of C++'s implicit type conversion mechanisms. Unfortunately, these mechanisms start to break down when you are calling overloaded functions (often operator<<, operator=, etc. have a number of overloads). In these cases you will get an "ambiguous overload" error message from the compiler and be forced to use the old explicit casting to resolve the situation.

In my opinion, this is a limitation of the C++ language or at least the implementation thereof. For example, I don't see why C++ shouldn't be able to resolve the implicit conversion on something like:

cdiggins::any a = std::string("Hi");
std::string b;
b = a;

as it is pretty clear that we are assigning to a string and would probably prefer to assign from a string as well if possible. Other cases are obviously not as clear cut.

I hope this perhaps answers your question a bit. There may also be other reasons or considerations why Mr. Diggins chose not to include the casting operator overload so I'll leave that for him to answer.

Memory Leaks and Crashes when storing "non-primitiv" data!

Raute11-Aug-10 3:57

Raute

11-Aug-10 3:57

we just evaluated this as an alternative to getting "boost" out of our public api ...

on first try/view it looked good ... but the code seems to contain some glitches (especially in copy-c'tor and assignment) ... I'll give some code examples for the found issues, so if somebody want to spent some time on it could fix it ...

Memory Leak example (only with "values" which contain allocated data):
<pre>
cdiggins::any foobar;
while(true)
{
foobar = std::string("12345678901234567890");
}
</pre>

... the assign (with same table) is missing a d'tor on the internal std::string, so the internal memory of std::string wont be freed
... hint: with VC2008 this only happens with strings bigger then 16char (because this std::string impl. contains a special "hack" for short strings)

Crash example (via multiple deletes on the same alloc):
struct foo_s { void* a; void* b; };
cdiggins::any foo = foo_s();
cdiggins::any bar = foo;
foo = bar;

... will crash at end of "block", when foo and bar get freed

Re: Memory Leaks and Crashes when storing "non-primitiv" data!

Christopher Diggins9-May-11 15:31

Christopher Diggins

9-May-11 15:31

Thank you for finding this problem. I rewrote the whole thing. Smile | :)

The new version is simpler, and I believe fixes the problems you found. Basically only a handful types now support the "small type" policy.

Christopher Diggins

Question on checking empty

Member 421168429-Mar-10 9:26

Member 4211684

29-Mar-10 9:26

I think, with this design, you won't be able to find out whether something is stored in cdiggins::any or not. So storing zero or leaving it empty has the same sense. Am i right?

Gokulakannan K.S.

Preventing Reallocations

Anand Krishnamoorthi18-Apr-07 6:15

Anand Krishnamoorthi

18-Apr-07 6:15

Right now allocation doesn't take place for types
whose size is <= sizeof( void *).

I think it would be useful if the function table structure
also stored the size of the type.

So for dynamically allocated objects of different classes
but that have the same object size, we can reuse the
memory after calling the destructor for existing object.

any_detail::fxn_ptr_table* x_table = any_detail::get_table<t>::get();
if (table == x_table) {

becomes something like:
any_detail::fxn_ptr_table* x_table = any_detail::get_table<t>::get();
if (table->size_ == x_table->size_ ) {
destruct existing object;
construct new object in place, on existing memory

Anand.

Small Types Assignment Problem?

Anand Krishnamoorthi18-Apr-07 6:10

Anand Krishnamoorthi

18-Apr-07 6:10

#include <cstdio>

struct Small {
~Small() { printf("small destructed\n"); }
};

int main()
{
cdiggins::any a;
a = Small();
a = Small();

}

The 2nd assignment fails to call the destructor of the Small object.
So output is

small destructed
small destructed
small destructed

There's another post that mentions this.

Anand.

Re: Small Types Assignment Problem?

xryl6695-Sep-07 2:28

xryl669

5-Sep-07 2:28

Anand Krishnamoorthi wrote:
The 2nd assignment fails to call the destructor of the Small object.
So output is

small destructed
small destructed
small destructed

From what I'm seeing, it's the expected output.

<br />
<br />
int main()<br />
{<br />
cdiggins::any a; // No Small created here<br />
a = Small(); // A Small is created here on the stack, a reference is taken on it, and another Small is allocated in the any, temporary object is destructed -> First line<br />
a = Small(); // A new Small is created, the any's inner object is overwritten with it (unless you use the last version on the forum), the temporary is destructed (second line)<br />
             // Small destructor is called here when any is destructed (third line)<br />
}<br />
<br />

I'm sure you are refering to the leak the some other people are talking about, but it's corrected since a long time now.

Compile problem with cast

Neville Franks17-Jul-06 13:15

Neville Franks

17-Jul-06 13:15

Hi,
I'm trying to use the example in the article with VC6 and get the following compile error. I'm using latest version from pablo_mag.

any a = 42;
int n = a.cast<int>();    // error C2062: type 'int' unexpected
int m = any_cast<int>(a);

I'm a Boost fan, but in this particular case I'd prefer not to have to use it.

Any suggestions?

Neville Franks, Author of Surfulater www.surfulater.com "Save what you Surf" and ED for Windows www.getsoft.com

Re: Compile problem with cast

pablo_mag17-Jul-06 14:00

pablo_mag

17-Jul-06 14:00

Unfortunately, VC6 doesn't support that syntax for calling member templates.

The closest one can get is something like the following:

<br />
any a = 42;<br />
int n = a.cast_(any::to<int>());<br />
int m = any_cast<int>(a);<br />

But that's obviously not as nice looking as cast<int>() would be.

Do you think it worth adding this?

Pablo Aguilar
pablo dot aguilar at gmail dot com

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