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Solution for Multiple enable_shared_from_this in Inheritance Tree

, 21 Nov 2011
The initial implementation of enable_shared_from_this of STL or the one from Boost C++ causes crash if it appears more than once in the inheritance tree of a user class. This is a solution for the problem. (search tag: enable shared from this)
EnableSharedFromThisV1.0.zip
EnableSharedFromThis
UsageExample
EnableSharedFromThis.vcxproj.filters
#include "../EnableSharedFromThis.h"
#include "../SmartPtrBuilder.h"
#include <memory>
#include <iostream>

using namespace Generic;

class Base;
class Derived;

void FuncBase(std::shared_ptr< Base > iBase);
void FuncDerived(std::shared_ptr< Derived > iDerived);

class Base : public EnableSharedFromThis< Base >
{
public:
  Base(int iValue) : mValue(iValue) {}
  void BaseFunc()
  {
    FuncBase(EnableSharedFromThis< Base >::SharedFromThis());
  }
  void PrintValue()
  {
    std::cout << "Value = " << mValue << std::endl;
  }
private:
  int mValue;
};

class Derived : public Base, public EnableSharedFromThis< Derived >
{
public:
  // Factory method
  static std::shared_ptr< Derived > Create(int iValue)
  {
    return SmartPtrBuilder::CreateSharedPtr< Derived, Base >(new Derived(iValue));
  }
  void DerivedFunc()
  {
    FuncDerived(EnableSharedFromThis< Derived >::SharedFromThis());
  }
private:
  Derived(int iValue) : Base(iValue) {}
};

void FuncBase(std::shared_ptr< Base > iBase)
{
  iBase->PrintValue();
}

void FuncDerived(std::shared_ptr< Derived > iDerived)
{
  iDerived->PrintValue();
}

int main()
{
  // Simply use the factory method to instanciate Derived
  std::shared_ptr< Derived > wDerived = Derived::Create(123);

  // One or both of the following would crash if using the original std::enable_shared_from_this
  wDerived->BaseFunc();
  wDerived->DerivedFunc();
  return 0;
}

// Copyright (C) 2011 by Philippe Cayouette
     
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
     
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
     
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

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This article, along with any associated source code and files, is licensed under The MIT License

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About the Author

Philippe Cayouette
Software Developer (Senior) CAE Inc.
Canada Canada
No Biography provided

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