[boost] Re: assert() replacement?

From: Valentin Bonnard (Bonnard.V_at_[hidden])
Date: 1999-08-31 12:27:39

Greg Colvin wrote:
> 
> From: Valentin Bonnard <Bonnard.V_at_[hidden]>
> > Greg Colvin wrote:
> > >
> > > From: Valentin Bonnard <Bonnard.V_at_[hidden]>
> > > > Greg Colvin wrote:
> > > > > ...
> > > > > So any user of Boost must define exactly one extern debug_mode in
> > > > > order to link?
> > > >
> > > > Yes. They must declare it in every TU which uses my macro
> > > > before uses of the macro.
> > >
> > > Which means in every translation unit that includes any Boost header?
> >
> > If Boost uses this macro in headers (not just .cc files), then
> > yes.
> 
> Ouch.
> 
> > > > There is no no-checks-by-default behaviour (there is no
> > > > default behaviour at all).
> > > >
> > > > They can use an static constant but it isn't recommanded.
> > > > They can use an auto variable.
> > > > > And being a link-time constant, the code for the condition cannot
> > > > > be compiled away?
> > > >
> > > > You do it as you want: compile time constant, ``link time''
> > > > constant, or even a variable. It's up to you.
> > > >
> > > > I recommend a compile-time constant with external linkage.
> > >
> > > You mean in each translation unit you would put something like this?
> > >
> > >    const debug_mode = MY_DEBUG;
> >
> > (const bool I guess)
> > I recommended a constant with *external* linkage.
> 
> Like so?
> 
>    extern const bool debug_mode = MY_DEBUG;

Yes

> > > Doesn't that break the ODR?  Or am I confused again?
> >
> > If MY_DEBUG is defined the same way in all headers, it's
> > fine. If not, _and_ you are using headers which use the
> > macro, then it breaks the ODR.
> 
> How do you square that with 3.2, paragraph 3:
> 
>   Every program shall contain exactly one definition of every non-inline
>   function or object  that  is  used  in  that  program;  no  diagnostic
>   required.

debug_mode should be defined in only one .cpp file

> > I leave the responsabillity to define debug_mode
> > consistently to the user.
> 
> Then I fail to see how this facility is superior to assert, except
> for throwing 

Because:
- it let the user 
  - use a global debug_mode, initialised once, with no risk 
    at all, or 
  - have one debug_mode.hpp header, with no redundancy
- it provides more granularity (debug_mode might have not 
  class scope)

I am merely giving my ideas, I am criticizing other's ideas, 
I am _not_ promoting anything.

-- 
Valentin Bonnard