std.experimental.logger formal review round 3

[Martin Nowak via Digitalmars-d]

On Tuesday, 28 October 2014 at 12:02:16 UTC, Robert burner 
Schadek wrote:
> It is a design goal to disable certain LogLevel at CT of a 
> compile unit (CU).
> e.g. make all logs to trace function template do nothing

One idea to make this working is to use prefixed version 
identifiers.
Obviously this is all boilerplate so it could be done in a mixin 
template in std.log.

module mylib.log;

version (MyLibLogInfo)
     enum logLevel = LogLevel.info;
version (MyLibLogTrace)
     enum logLevel = LogLevel.trace;
version (MyLibLogWarning)
     enum logLevel = LogLevel.warning;
version (MyLibLogError)
     enum logLevel = LogLevel.error;

static if (is(typeof(logLevel)))
{
     // wrapper around Logger interface/class for CT logLevel
     static struct FixedLogLevel
     {
         enum logLevel = logLevel;
         Logger impl;
         alias impl this;
     }

     void setLogger(Logger logger)
     {
         logger.impl = logger;
     }

     private __gshared FixedLogLevel logger;
}

module mylib.foo;

void foo()
{
     import mylib.log;
     logger.info("bla");
     logger.error("wat");
}

module client.bar;

void bar()
{
     import mylib.log, mylib.foo;
     auto logger = new FileLogger("log.txt", LogLevel.warning);
     setLogger(logger);
     foo(); // CT check for LogLevel
     logger.info("runtime check whether info logging is on");
}