Re: [Boost-users] Scoped Pairs of functions?

Subject: Re: [Boost-users] Scoped Pairs of functions?
From: Nat Linden (nat_at_[hidden])
Date: 2011-08-18 13:04:16

On Wed, Aug 17, 2011 at 10:49 AM, Brian Allison
<brian.w.allison_at_[hidden]> wrote:

>   I'm on a project which uses a C++ compiler, but with a lot of C-isms. One of those is that there are objects with pairs of functions which allocate/deallocate resources. I don't have time to fix all of the design issues with the classes that do this (yet), but within one compilation unit I'd like to remove the chance for leaks.
>
>   So - if I wanted to use boost types to wrap around 2 functions f() and g(), where each function
>
> has a void or primitive return type
> takes zero or 1 argument
> where f() is called at some point in a scope, and then g() is called on exiting the scope from which f() is called and only if f() doesn't throw..
> has its return value ignored. [Gahh....]
>
> Is there a boost::bind (or lambda) expression that I can wrap in a type?
>
> How do I generalize to include the possibility of a single argument?

The following works for me with gcc 4.0.1 (yeah, I know, old compiler):

#include <iostream>
#include <boost/function.hpp>
#include <boost/bind.hpp>

void acquire_fixed()
{
    std::cout << "Acquiring fixed resource\n";
}

void release_fixed()
{
    std::cout << "Releasing fixed resource\n";
}

void acquire(const std::string& resource)
{
    std::cout << "Acquiring " << resource << '\n';
}

void release(const std::string& resource)
{
    std::cout << "Releasing " << resource << '\n';
}

class ScopedResource
{
public:
    typedef boost::function<void()> ResourceFunc;
    ScopedResource(const ResourceFunc& acq, const ResourceFunc& rel):
        mRelease(rel)
    {
        acq();
    }

    virtual ~ScopedResource()
    {
        mRelease();
    }

private:
    ResourceFunc mRelease;
};

int main(int argc, char *argv[])
{
    {
        ScopedResource fixed(acquire_fixed, release_fixed);
        std::cout << "during lifespan of 'fixed'\n";
    }
    {
        ScopedResource something(boost::bind(acquire, "something"),
                                 boost::bind(release, "something"));
        std::cout << "during lifespan of 'something'\n";
    }
    return 0;
}