Re: [boost] Re: First lambda

From: John Torjo (john.lists_at_[hidden])
Date: 2004-03-08 11:10:56

David Abrahams wrote:

>John Torjo <john.lists_at_[hidden]> writes:
>
>  
>
>>Aleksey Gurtovoy wrote:
>>
>>    
>>
>>>David Abrahams wrote:
>>> 
>>>
>>>      
>>>
>>>>I just tried using the lambda library for the first time.  Here's
>>>>what came out of it, after some struggle:
>>>>
>>>> #include <boost/lambda/lambda.hpp>
>>>> #include <vector>
>>>> #include <numeric>
>>>>
>>>> using namespace boost::lambda;
>>>>
>>>> struct X
>>>> {
>>>>     X() : count(1) {}
>>>>
>>>>     unsigned long count;
>>>> };
>>>>
>>>> std::vector<X> xs(10);
>>>> unsigned long n = std::accumulate(
>>>>     xs.begin(), xs.end(), 0UL,
>>>>     _1 + (&_2) ->* &X::count);
>>>>   
>>>>
>>>>        
>>>>
>>>Views make it much cleaner, both conceptually and syntactically:
>>>
>>>   unsigned long n = accumulate(          transform_view( xs,
>>>mem_fn(&X::count) )
>>>       , 0UL
>>>       );
>>>        
>>>
>>>      
>>>
>>Indeed ;)
>>Using views/ranges makes the code much simpler/clearer.
>>
>>In time, I've accepted the fact that there's not much point in using
>>in-place functions (like _1 + _2, etc.), since in real-life they just
>>complicate the code.
>>So I just create a new function (in anonymous namespace), and that's it.
>>
>>And I use boost::bind, which rocks big time :D
>>    
>>
>
>What do you suppose boost::bind does other than creating an in-place
>function?  I believe you guys are confusing issues.  While I think
>  
>
Of course, I knew that ;) I did misexplain however. What I should have 
said was that I prefer to create a simple and straightforward function 
(usually a one-liner) and use it with boost::bind over using 
boost::lambda. Makes the code more self-explanatory.

>views have benefits, the problems I mentioned above were not caused by
>the use of iterators or in-place functions:
>
>  std::vector<X> xs(10);
>  unsigned long n = std::accumulate(
>      xs.begin(), xs.end(), 0UL,
>      _1 + bind(&X::count, _2));
>    
>Is really no worse than the alternative cited above:
>
>  unsigned long n = accumulate(          
>      transform_view( 
>        xs, mem_fn(&X::count) ) 
>    , 0UL);
>
>  
>
what we were trying to say was that if you use views/ranges, problems 
like the one you've shown above usually don't appear/ appear very seldom 
(at least to me ;) ).

Best,
John