Variable arguments with file and line information?

[Timothee Cour]

unfortunately this problem keeps arising every so often and the only thing
we have are workarounds

to name a few:
digitalmars.D - Typesafe variadics in any position
feature request: special optional argument (__FILE__, ...) AFTER variadic
template


On Sat, Nov 16, 2013 at 3:55 PM, Jonathan M Davis <jmdavisProg at gmx.com>wrote:

> 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
>
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