unique_ptr example from effective modern c++

unique_ptr.cpp

//////////////////////////////////////////
// std::unique_ptr usage
// - factory function return type for 
//   objects in a hierarchy.
//////////////////////////////////////////

//////////////////////////////////////////
// factory function with custom deleter
//////////////////////////////////////////
class Investment 
{ 
public:
    ... 
    virtual ~Investment();
    ...
};

class Stock : public Investment { ... }; 
class Bond : public Investment { ... }; 
class RealEstate : public Investment { ... };

audo deleteInvestment = [](Investment* pInvestment)
{
    makeLogEntry(pInvestment);
    delete pInvestment;
};

template<typename... Ts>  
auto makeInvestment(Ts&&... params) // C++14
{
    std::unique_ptr<Investment, decltype(deleteInvestment)>
        pInv(nullptr, deleteInvestment);

    if ( /* a Stock object should be created */ )
    {
        pInv.reset(new Stock(std::forward<Ts>(params)...);
    }
    else if ( /* a Bond object should be created */ ) 
    { 
        pInv.reset(new Bond(std::forward<Ts>(params)...); 
    }
    else if ( /* a RealEstate object should be created */ )  
    { 
        pInv.reset(new RealEstate(std::forward<Ts>(params)...);  
    }

    return pInv;
}


//////////////////////////////////////////
// usage 
//////////////////////////////////////////
void usage() 
{ 
    ... 
    
    // pInvestment is of type std::unique_ptr<Investment>
    auto pInvestment = makeInvestment(arguments);
    ... 
}