Re: [boost] Re: First lambda

From: Joel de Guzman (joel_at_[hidden])
Date: 2004-03-03 21:41:12

Powell, Gary wrote:

>>>// PROPOSED CHANGE IN SOME FUTURE PAPER
>>>
>>>unsigned long n = std::accumulate(
>>>      xs.begin(), xs.end(), 0UL,
>>>          long (long lhs, X const &rhs)     // inline fn with no name.
>>>          {
>>>              return lhs + rhs.count;
>>>          }
>>>      );
> 
> 
>>Yeah, but do you propose to make local names visible inside the anonymous
>>function, or not? If you do, you open a big can of worms for implementations
>>(recursive nested functions, need I say more?), if you don't, BLL can still
>>do things that anonymous functions can not. Anonymous functors could help
>>some, but their syntax won't be quite as compact as your example above.

I'd asume it can also handle nested anonymous functions? Say, for
example, I wish to print all the contents of a 2D vector-of-vector:

     std::vector<std::vector<int> vv;

     std::for_each(vv.begin(), vv.end(),
         void (vector<int> const& v)
         {
             std::for_each(v.begin(), v.end(),
                 void (int x)
                 {
                     cout << x << endl;
                 }
         }
     );

Now, to complicate matters, what if I wish to access v in the
inner anonymous function? Can you also do that? Example:

     std::for_each(vv.begin(), vv.end(),
         void (vector<int> const& v)
         {
             std::for_each(v.begin(), v.end(),
                 void (int x)
                 {
                     cout << x << endl;
                     do_fomething_with(v); // <<--here
                 }
         }
     );

Cheers,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net