Re: [Boost-users] [foreach] boost_foreach_is_lightweight_proxy doesn't work

From: Raider (sraider_at_[hidden])
Date: 2007-07-23 17:29:26

> Better, but you have proxied a non-const vector, and you're presenting a 
> const interface. Try this:
> 
>    class vec
>    {
>    public:
>         vec(sv& v = global) : v_(v) {}
>         typedef sv::iterator iterator;
>         typedef sv::iterator const_iterator;
>         typedef sv::const_iterator const_iterator;
>         iterator begin() const { return v_.begin(); }
>         iterator end() const { return v_.end(); }
>         void push_back(const string& s) const { v_.push_back(s); }
>    private:
>         sv& v_;
>    };
> 
> The const-ness of the proxy itself shouldn't matter. Only the const-ness 
> of the proxied object should matter.
> 

I want const_iterator to be dereferencable to const object and iterator 
to non-cont object. Like this:

class vec
{
public:
     vec(sv& v = global) : v_(v) {}
     typedef sv::iterator iterator;
     typedef sv::const_iterator const_iterator;
     iterator begin() const { return v_.begin(); }
     iterator end() const { return v_.end(); }
     void push_back(const string& s) const { v_.push_back(s); }
private:
     sv& v_;
};

This allows me make no difference does GetVector() return `vec' type 
(proxy) or `sv&' (reference to the real container):

for (xxx::iterator it(GetVector().begin(), end(GetVector().end());
     it != end; ++it) { modify(*it); }

for (xxx::const_iterator it(GetVector().begin(), end(GetVector().end());
     it != end; ++it)
{
   /*
   here I'm SURE that (*it) is READ-ONLY:
   this knowlege make my code safer
   because comiler will detect mutations and disallow them
   */
}

I want to use BOOST_FOREACH instead of `for' statements above to:
1. don't care that `xxx' type is
2. call GetVector() only once

Now I found some unsteady way:
#define BOOST_FOREACH_NO_RVALUE_DETECTION
makes my code compile. I'll try to dig in this direction.