Debug output functions

[nazriel]

On Tuesday, 3 July 2012 at 03:15:02 UTC, Wouter Verhelst wrote:
>
> So, I wanted to create a number of functions that would call 
> write(),
> writef(), writefln(), or writeln() with whatever arguments they 
> were
> given, but only if the user had used a 'enable debugging' 
> command-line
> option (or some such).
>
> What I first did was this:
>
> module debugout;
>
> int debuglevel;
>
> void set_level(int level) {
> 	debuglevel = level;
> }
>
> auto tdebug(func)(int level, ...) {
> 	va_list va;
> 	va_start(va, level);
> 	if(debuglevel <= level) {
> 		return func(va);
> 	}
> 	va_end(va);
> }
>
> alias tdebug!(write) wdebug;
> alias tdebug!(writef) wdebugf;
> (... and so on...)
>
> but that didn't work:
>
> debugout.d(20): Error: template instance tdebug!(write) 
> tdebug!(write) does not match template declaration tdebug(func)
>
> I had a short look at 
> http://dlang.org/variadic-function-templates.html
> which would seem to be a somewhat better way of implementing 
> this, but I
> can't figure out how exactly I should go forward, then.
>
> I do believe that something like the following would do what I 
> want:
>
> auto wdebug(level, ...) {
> 	va_list va;
> 	va_start(va, level);
> 	writefx(stdout, ???, va);
> 	va_end(va);
> }
>
> except the va_list stuff doesn't seem to be necessary, I don't 
> know what
> to put in place of the "???", and I'd have to write this four 
> times
> rather than being able to template it four times.
>
> How should I do this instead?

http://dpaste.dzfl.pl/3efd9c1b - try this.