Any ideas how one can achieve what is written in the subject line?

f below does achieve this but I one would expect that it produces
significant template bloat.

g achieves the aim but isn't very elegant.

import std;
void f(string file=__FILE__,size_t line=__LINE__,R...)(R r)
{
  writeln(file,":",line," ",r);
}
void g(T)(T t,string file=__FILE__,size_t line=__LINE__)
{
     writeln(file,":",line," ",t.expand);
}

void main()
{
   f("hello ", 123);
   g(tuple("hello ",123));
}

On Tuesday, 25 January 2022 at 12:11:01 UTC, JG wrote:

void f(T...)(auto ref T args, string file = __FILE__, int line = __LINE__)
{
    writeln(file, ":", line, ": ", args);
}

On Tuesday, 25 January 2022 at 12:27:16 UTC, Dennis wrote:

void f(T...)(auto ref T args, string file = __FILE__, int line = __LINE__)
{
    writeln(file, ":", line, ": ", args);
}

note: default arguments after variadic arguments are supported since D 2.079.0: https://dlang.org/changelog/2.079.0.html#default_after_variadic

On Tuesday, 25 January 2022 at 12:27:16 UTC, Dennis wrote:

void f(T...)(auto ref T args, string file = __FILE__, int line = __LINE__)
{
    writeln(file, ":", line, ": ", args);
}

Thank you very much.