Gennadiy Rozental writes:

I noticed that in some places we are using extra namespace for protection from unintended ADL.

It would help the discussion if you pinpointed these particular places. The answers below are MPL-specific.

Is there any rationale for:

1. Why we need that?

See http://www.mail-archive.com/boost@lists.boost.org/msg01741.html and http://thread.gmane.org/gmane.comp.lib.boost.devel/90627.

2. Why namely this solution is prefered?

It's the only known way to resolve the issue.

3. In which case we need to do so?

See the links above. -- Aleksey Gurtovoy MetaCommunications Engineering