[boost] Re: boost::filesystem file restrictions

From: David Abrahams (dave_at_[hidden])
Date: 2003-08-14 14:30:51

Beman Dawes <bdawes_at_[hidden]> writes:

>     typedef bool (*is_portable_test)( string & candidate );
>
>     class scoped_portability_policy : noncopyable
>     {
>     public:
>       explicit scoped_portabiity_policy( is_portable_test f );
>       ~scoped_portabiity_policy();
>      };
>
> The effect of constructing a scoped_portability_policy is to push p
> onto a stack. The destructor pops the stack. Class path uses the top
> stack entry as the current portability checker. The stack is
> initialized with a default portability checker.
>
> Most programs which wanted a policy other than the default would just
> being something like this:
>
>    int main()
>    {
>       scoped_portability_policy( posix_portability_check );
>       ...
>
> Although the stack is global, when coupled with
> scoped_portability_policy, it is safer than a single global variable
> (because library functions which push are guaranteed to pop.)
>
> Of course it can be subverted by static or heap allocation. (Aside: Is
> there a reliable way to prevent static or heap allocation?)
>
> I'm curious to hear what others would think of the above scheme.

It's expensive to make threadsafe, since it requires a global.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com