Re: [boost] casting a shared_ptr from void with custom deleter

Subject: Re: [boost] casting a shared_ptr from void with custom deleter
From: Kenny Riddile (kfriddile_at_[hidden])
Date: 2009-03-20 18:07:53

Christopher Currie wrote:
> On Fri, Mar 20, 2009 at 7:03 AM, Peter Dimov <pdimov_at_[hidden]> wrote:
>> Kenny Riddile:
>>> I'm trying to do something like this:
>>>
>>> boost::shared_ptr<const Foo> fooPtr( boost::static_pointer_cast<const
>>> Foo>(typeErasedFoo), CustomDeleter<const Foo>() );
>>>
>>> where typeErasedFoo is of type:
>>>
>>> boost::shared_ptr<const void>
> 
> Just to clarify Peter's point, deletion policy decisions should be
> made at initialization time, not as a part of a type conversion. So,
> your original object construction, which you don't show, should set
> your custom deleter when you create the pointer that receives your
> "new Foo".
> 
> A custom deleter is a part of the underlying "value" of the smart
> pointer, and as such are preserved across casts, so there shouldn't be
> a need for the kind of call you're trying to do. The code below
> demonstrates what I mean:
> 
> #include <iostream>
> #include <boost/shared_ptr.hpp>
> 
> struct Foo{};
> 
> struct FooDeleter{
>   void operator()( Foo* f ) {
>     std::cout << "Goodbye, cruel world!";
>     delete f;
>   }
> };
> 
> int main() {
> 
>   boost::shared_ptr<Foo> pFoo;
> 
>   {
>     boost::shared_ptr<void> pVoid;
> 
>     {
>        boost::shared_ptr<Foo> pTmp( new Foo, FooDeleter() );
>        pVoid = pTmp;
>     }
> 
>     pFoo = boost::static_pointer_cast<Foo>( pVoid );
> 
>   }
> 
>   // emits "Goodbye, cruel world!" when pFoo is destructed.
> }
> 
> Naturally, you don't have to use a shared_ptr<Foo> when you first
> allocate the Foo object, it's perfectly valid for the pTmp variable to
> be eliminated and simply declare: boost::shared_ptr<void> pVoid( new
> Foo, FooDeleter() );
> 
> HTH,
> Christopher
> _______________________________________________
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>

Ya, this all makes perfect sense and I was just being stupid due to lack 
of sleep.  I've got it working now (with much simpler code).  Thanks guys!