Using glog's design for Phobos?

[Steven Schveighoffer]

On Thu, 26 Aug 2010 18:19:24 -0400, Tomek Sowiński <just at ask.me> wrote:

> Dnia 26-08-2010 o 05:59:19 Andrei Alexandrescu  
> <SeeWebsiteForEmail at erdani.org> napisał(a):
>
>> At my workplace we're using Google's logging library glog  
>> (http://google-glog.googlecode.com/svn/trunk/doc/glog.html), and the  
>> more I use it, the more I like it. It's simple, to the point, and  
>> effective.
>>
>> I was thinking it would be great to adapt a similar design into Phobos.  
>> There will be differences such as use of regular argument lists instead  
>> of << etc., but the spirit will be similar. What do you think?
>
> Hm.. why not. Some quick thoughts:
>
> * Only a subset of features needs to be ported, e.g.
> DLOG(...) == version(debug) LOG(...)
> CHECK == enforce()
> Also, I don't get the superlativeness of LOG_IF(INFO, pred) << ...   
> versus  if (pred) LOG(INFO) << ...

I think I know why, without even looking at the code.  A typical issue  
with logging is that you want to evaluate the log output level, which is  
always an O(1) operation, before evaluating any other items which may be  
expensive, such as a custom predicate or message.

i.e. LOG_IF probably does this:

if(log.level >= INFO && pred)

This is one of the only reasons I think we need a macro system.  Mixins  
can do this, but who wants to always write mixin when doing logging?

lazy is traditionally used, but it has costs as well.  The best solution  
is to have a macro that converts:

log.info(msg);

directly into:

if(log.level >= info) log.output(msg);

which doesn't require lazy and is exactly what you *should* write.

> * Instead of LOG(INFO, msg), please go for Log.info(msg).

Most likely, this is due to the same thing.

-Steve