Re: [boost] [bind/lambda] a functor holding a shared_ptr

From: Steven Watanabe (steven_at_[hidden])
Date: 2007-01-12 16:19:16

AMDG

Yuval Ronen wrote:
> In the following code:
>
> struct A
> {
>      void func();
> }
>
> int main()
> {
>      shared_ptr<A> a(new A);
>      boost::bind(&A::func, a);
> }
>
> the bind() call returns a function object which holds the shared_ptr by 
> value (it's one of the shared owners). This is an important feature I'm 
> using, because sometimes the functor is the last owner left standing, 
> and I want to keep A alive until the functor's destructor (actually, I 
> don't really like this design, but I'm talking about legacy code here). 
> Replacing boost::bind with lambda::bind doesn't compile. Is this feature 
> not supported by lambda::bind? If not supported now, is it planned to be 
> supported in the future? Can I in the mean time implement this feature 
> in my code with relative ease?
>
> Thanks,
> Yuval
You can explicitly dereference the shared_ptr.

#include <boost/shared_ptr.hpp>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>

struct A
{
    void func() {}
};

template<class T>
struct identity_t {
    mutable T t;
    template<class Args>
    struct sig {
        typedef T& type;
    };
    identity_t(const T& arg) : t(arg) {}
    T& operator()() const {
        return(t);
    }
};

template<class T>
identity_t<T> identity(const T& t) {
    return(t);
}

int main()
{
    boost::shared_ptr<A> a(new A);
    boost::lambda::bind(&A::func, *boost::lambda::bind(identity(a)))();
}

In Christ,
Steven Watanabe