[boost] Global object initialization [was: Phoenix-2 prerelease]

From: David Abrahams (dave_at_[hidden])
Date: 2005-11-04 11:55:20

Joel de Guzman <joel_at_[hidden]> writes:

> Comments, feedback very welcome!

   Here are some sample preset definitions of arg1..argN

  actor<argument<0> > const arg1 = argument<0>();
  actor<argument<1> > const arg2 = argument<1>();
  actor<argument<2> > const arg3 = argument<2>();

  and its BLL_1.._N style counterparts:

You shouldn't use the BLL abbrev., especially not without introducing
it first.  I suggest "Boost.Lambda"

  actor<argument<0> > const _1 = argument<0>();
  actor<argument<1> > const _2 = argument<1>();
  actor<argument<2> > const _3 = argument<2>();

Have you considered the ODR/initialization order implications of
this?

Eric and I have been discussing this in another context, and it seems
to us that you have a choice:

 1. The placeholders are statically initialized const POD objects in
    an unnamed namespace and you have likely ODR violation when used
    by templates in multiple translation units.

 2. The placeholders are dynamically initialized references in an
    unnamed namespace and you risk undefined behavior when they are
    used without initialization due to initialization order issues

 3. The placeholders are dynamically initialized objects in an unnamed
    namespace, and you have likely ODR violation *and* initialization
    order issues

Seems from the doc like you have #3, which is the worst of both
worlds.  No?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com