Re: [Boost-users] BOOST_FOREACH with Index

Subject: Re: [Boost-users] BOOST_FOREACH with Index
From: Eric Niebler (eric_at_[hidden])
Date: 2009-12-13 17:53:00

The Dude wrote:
> Eric Niebler wrote:
>>     Why not:
>> 
>>      int index = 0;
>> 
>>      BOOST_FOREACH(const Foo &f, foos)
>>      {
>>        // ... stuff ...
>>        ++index;
>>      }
>> 
>>     ?
> 
>   Thanks for you answer. I'm not sure how to answer the "why not"? The 
> code you write certainly will work, but so would the predecessor to 
> BOOST_FOREACH in the first place, no? So here's my attempt:
> 1. For shorter loops, this changes 2 LOCs to 5.

So put it all on one line! Kidding. ;-)

> 2. For longer loops, the iteration code changes its meaning if it 
> appears before the ++index or after.
> 3. The variable index has scope outside the loop.
> 4. Other people think so, e.g., the author's of D language 
> http://en.wikipedia.org/wiki/D_(programming_language)#Example_1
>   It's true that none of these points is really a proof. Still, I'd be 
> really happy to hack my own INDEX_FOREACH, but the 500+ LOCs of 
> BOOST_FOREACH left me daunted.

This is true, but I'm not convinced. What value BOOST_FOREACH has comes 
primarily from its ability to simplify something that's already pretty 
darn simple -- a plain for(;;) loop. I strongly resist any effort to 
make BOOST_FOREACH more complicated, unless the wins are truly 
significant. In this case, I don't think they are.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com