Re: [boost] [smart_ptr] make_shared usage

From: vicente.botet (vicente.botet_at_[hidden])
Date: 2008-07-28 02:17:40

----- Original Message ----- 
From: "Peter Dimov" <pdimov_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Sunday, July 27, 2008 5:25 PM
Subject: Re: [boost] [smart_ptr] make_shared usage

>
> Daniel Frey:
>
>> Hi,
>>
>> I have a question on make_shared. Consider a class which intends to
>> force all instances to be handled via a shared_ptr. I used to do this by
>> putting the ctors into the private section and adding static
>> create()-methods in the public section. Example:
>>
>> class X
>> {
>> private:
>>   X( int, double );
>>
>> public:
>>   static shared_ptr<X> create( int i, double d )
>>   {
>>      return shared_ptr<X>( new X( i, d ) );
>>   }
>> };
>>
>> Replacing the returned expression with make_shared<X>( i, d ) wouldn't
>> work, since it requires a public ctor.
>
> You should be able to make it work by making the appropriate make_shared 
> overload a friend:
>
> template< class T, class A1, class A2 >
> friend
> boost::shared_ptr< T > boost::make_shared( A1 const & a1, A2 const & a2 );

If you declare the boost::make_shared friend, the utility of the create 
function is questionable.

shared_ptr<X> x1_ptr = X::create(0,0);
shared_ptr<X> x2_ptr = boost::make_shared <X>(0,0);

The make_shared<X> function states clearly that the result is a 
shared_ptr<X>.

Vicente