Mixin and function template?

[renoX]

Hello,

I have a template which contain a single function:
template sputf(A...)
{
	char[] call()
	{
		auto fd=std.c.stdio.fopen("tmp_file", "w+");
		mixin(`fwritef(fd,`~Fmt!(A)~`);`);	
		std.c.stdio.fclose(fd);
		auto res = cast(char[])read("tmp_file");
		return res;
	}
}
At the call site, I have to do the following:
	mixin sputf!("%d{x}") P1;
	res = P1.call();
which is quite ugly, so I'd like to convert the code in a 'function template' but when I do this, I don't manage to call the function without failure..
Does someone knows how to do it?

Regards,
renoX