Re: [boost] Range Adapters (map_keys, map_values) cause undefined behavior (segv, etc) when applied to R-Values, especially in the context of BOOST_FOREACH

Subject: Re: [boost] Range Adapters (map_keys, map_values) cause undefined behavior (segv, etc) when applied to R-Values, especially in the context of BOOST_FOREACH
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2014-01-29 20:41:00

Hi Igor,

This is a known issue: see https://svn.boost.org/trac/boost/ticket/7630.
(That bug talks about C++11 range-based for loops, but the issue with
BOOST_FOREACH is the same).

I'm not sure what the status of this bug is. Jeffrey Yasskin posted a
patch to that bug which I reviewed over email, but I haven't heard
from him about it since.

Note that if you use C++11, a workaround is to use boost::for_each
with a lambda instead, so

  BOOST_FOREACH(SomeType v, range_rvalue | adaptor)
  {
      statements
  }

turns into
  
  boost::for_each(range_rvalue | adaptor, [&](SomeType v)
  {
      statements
  });

Since the temporary lives until the end of the statement, and the
whole loop is contained within the statement, there is no more
undefined behaviour.

Regards,
Nate