Re: [boost] [Proto] Access to member in proto expression tree

From: Eric Niebler (eric_at_[hidden])
Date: 2007-07-02 18:09:55

dan marsden wrote:
> Hi Eric
> 
> Thanks for all the help so far. I'm now filling out my prototype if/else implementation, mainly following your excellent recipe, and I've encountered a little annoyance.
> 
> If I write an expression like:
> 
> _1 + _2
> 
> ADL finds all the necessary operators etc in boost::proto (_1 and _2 are my placeholders in the phoenix namespace, using your extends mechanism), so it can built the right expression tree. All good so far.

Actually, the operators, proto::expr and proto::extends have recently 
moved into the proto::ops namespace for an ADL reason unrelated to 
yours. expr and extends are made available in the proto namespace with a 
using declaration.

> If I now write:
> 
> if_(_1 == _2)[stuff...] // stuff... is unimportant
> 
> Unfortunately proto::if_ is pulled in. This means I have to qualify phoenix::if_, which looks a bit too verbose for a lambda library. I think this could be addressed by moving the stuff that does not pertain to expression tree generation out of the boost::proto namespace, and into another boost::proto::other_stuff namespace, so the chances of it being pulled during tree construction are reduced, and I can have my unqualified syntax back. Is this possible? Or have I missed something on my side that could prevent this happening?

Oh man. This ADL stuff .... grrrr. OK, I need to shuffle some stuff 
around. Thanks for the heads up.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com