Using glog's design for Phobos?

[Stanislav Blinov]

  27.08.2010 17:49, Steven Schveighoffer wrote:
> 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.
>
Hmm... something like this can be done with opDispatch:

---

import std.typecons;

mixin(defineEnum!("LogLevel",  "error", "info"));

struct Log
{

     LogLevel level;

     template isLogLevel(string m)
     {
         enum isLogLevel = __traits(hasMember, LogLevel, m);
     }

     void opDispatch(string m, Args...)(lazy Args a) if (Log.isLogLevel!(m))
     {
         LogLevel l;
         enumFromString(m,l);
         if (level >= l)
         {
             writef("%s ", m);
             writefln(a);
         }
     }
}

void main()
{
     Log log;

     log.level = LogLevel.error;

     log.error("Error!"); // printed
     log.info("Info!");   // not printed

     log.level = LogLevel.info;

     log.error("Error!"); // printed
     log.info("Info!");   // printed

     log.warning("Warning!"); // does not compile

}

---

It does however use lazy, but not mixins, and does not require any 
macros :) And it is safe.