Variable arguments with file and line information?

[Jonathan M Davis]

On Sunday, November 17, 2013 00:09:53 Namespace wrote:
> On Saturday, 16 November 2013 at 22:57:35 UTC, Namespace wrote:
> > Hi.
> > Is it possible to write something like that?
> > ----
> > void error(Args...)(string msg, Args args, string file =
> > __FILE__, size_t line = __LINE__) { ... }
> > ----
> > ?
> > Currently not, but how could it be done? I wont like to write:
> > ----
> > error(format(msg, args));
> > ----
> > 
> > Thanks in advance. :)
> 
> It is always surprising how quickly one has found its own
> solution, after you have posted here... :)
> 
> ----
> import std.stdio;
> import std.string : format;
> 
> template error(string file = __FILE__, size_t line = __LINE__,
> Args...) {
> 	void error(string msg, Args args) {
> 		static if (args.length != 0)
> 			msg = .format(msg, args);
> 
> 		writeln(.format(msg ~ ". In file %s on line %d.", file, line));
> 	}
> }
> 
> void main()
> {
> 	error("hallo");
> 	error("Hallo %s.", "du da");
> }
> ----

If you're dealing with variadic arguments, then making the file and line number 
be template arguments is really your only solution. However, I must warn you 
that that will result in a new template instantation _every_ time that you use 
error, because the file and line number are always going to be different unless 
you call the function multiple times on the same line). So, this approach is 
pretty much guaranteed to generate template bloat. That may be acceptable, but 
I'd personally suggest trying to find a different way to go about solving the 
problem unless error is not going to be called very often - e.g. force the 
caller to call format when creating the message rather than supporting 
variadic arguments directly in error.

- Jonathan M Davis