Re: [boost] First lambda

From: Joel de Guzman (joel_at_[hidden])
Date: 2004-03-03 22:26:44

Shannon Stewman wrote:

> On Wed, Mar 03, 2004 at 01:34:50PM -0800, Powell, Gary wrote:
> 
> 
>>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;
>>          }
>>      );
> 
> 
> This seems to cast out the type inference present in BLL.  I think
> that's one of the nicer concepts in the lambda library, and a real
> boon to programming.  In my limited experience with SML/OCaml, type
> inference seems a better, safer, and more convenient way to program,
> albeit requiring a lot more compiler intelligence.  As BLL shows, though,
> this is quite possible, though perhaps limited, with existing C++.

I agree. In many cases, type inference is a necessity since
you do not know the type of the arguments before hand. Take
a simple Spirit parser, for example:

     std::string s;
     identifier = (+alpha_p)
         [ ref(s) = construct_<std::string>(arg1, arg2) ]
         ;

At grammar declaration time, we don't (can't) know the
exact type of arg1 and arg2. We simply know that they are
iterators.

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