Re: [boost] First lambda

From: Darren Cook (darren_at_[hidden])
Date: 2004-03-03 18:22:47

> Meantime it again highlights that a core language change to allow anonymous fns is needed so this whole mechanism of BLL can go away.
> 
> // 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;
>           }
>       );

I was hoping the syntax would be:

  unsigned long n = std::accumulate(
        xs.begin(), xs.end(), 0UL,{
            return _1 + _2.count;
            }
        );

With the option of this when you want different names:
  unsigned long n = std::accumulate(
        xs.begin(), xs.end(), 0UL, lambda(lhs,rhs){
            return lhs + rhs.count;
            }
        );

Incidentally, frustrated with the limits of BLL syntax I've moved to using 
macros for the most common cases in one of my programs (e.g. for each 
element in a specific container). I went through and replaced all 
std::for_each calls, and all for/while loops.

The macro looks very much like the syntax above and the code ended up 
shorter, clearer, and also uncovered some bugs: it turns out I'd written a 
loop with "i!=c.begin()" instead of "i!=c.end()". The macro always gets that 
right.

Max Motovilov wrote:
> 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?)

I think local names visible inside the anonymous function is the expected 
behaviour.

Can you say more about the potential problems (or point me to a 
paper/discussion if this is well-discussed somewhere else)?

Darren