RE: [Boost-users] Re: Bug in boost::lambda using operator <<?

From: Richard_Cox_at_[hidden]
Date: 2005-02-05 04:54:22

On Friday, February 04, 2005 5:47 PM Kevin Wheatley wrote:
> 
> Richard_Cox_at_[hidden] wrote:
> > 
> > The program below outputs
> > 
> >   String: <First string> Second string> Fourth string> Fifth string>
> > 
> > All but the first "<" is missing. Any ideas?
> >     std::for_each(coll.begin(), coll.end(), out << gt << _1 
> << L"> ");
> 
> 
> does this work?
> 
> std::for_each(coll.begin(), coll.end(), out << var(gt) << _1 << L">
> ");
> 
> not sure of the fix, but out << gt associates left to right and is
> evaluated once and has the type of out, you want it lazy evaluated so
> that the whole of the expression is considered as one... see the
> delaying constants and variables section of the lambda documents.
> 
> Kevin

Of course, "obvious" now :-(

out << gt

would evaluate returning the wostream which the lambda expression
created from the 2nd and 3rd <<'s then operates on.

Many thanks.

Richard
All opinions are mine and do not represent in any way the position of
Dell Corporation.