dmd 2.029 release

[Joel C. Salomon]

Georg Wrede wrote:
> Don wrote:
>> Georg Wrede wrote:
>>> One thing we sholuld be wary of is overdesign. BigInt is ok, but by
>>> the time we try to include a class called
>>> CompleteSimulationOfAnF1RaceCar, we're screwed. :-)  I see no way to
>>> incorporate them into writefln or even plain writeln. Or at least, no
>>> *use*.
>>
>> I think it'd be reasonable to limit things to the options available
>> for built-in types. Outside of that, custom formatting functions make
>> a lot of sense. The problem is that toString() _looks_ like it
>> emulates built-in formatting, but it only does '%s'. So it's really
>> beguiling.
> 
> Heh, one thought is, suppose we could have arbitrary format
> specifications in writef. Say, if we wrote %&lkjasdf; this string would
> be passed to toString. (It would of course be up to the class to
> error-check the string, writefln obviously cant (or shouldn't) do it.)
> 
> So, things are doable. But I'm really not looking forward to that kind
> of sports. Any elaborate printing or formatting should be handled
> outside writefln &co.

Take a look at the formatting library for Plan 9.  It’s very much like
printf & co., except it exposes enough of its internals to allow for new
formats to be added in.  See the documentation (for the *nix-ported
version) at <http://swtch.com/plan9port/man/man3/print.html> and
<http://swtch.com/plan9port/man/man3/fmtinstall.html>. For example:

typedef
struct {
	double	r, i;
} Complex;
#pragma  varargck  type "X"  Complex	// compiler checks type-safety

int
Xfmt(Fmt *f)
{
	Complex c;
	c = va_arg(f−>args, Complex);
	return fmtprint(f, "(%g,%g)", c.r, c.i); // can use flags here
}

main(...)
{
	Complex x = (Complex){ 1.5, −2.3 };
	fmtinstall('X', Xfmt);
	print("x = %X\n", x);
}

With D’s type-safe variadic functions, this model can be made really
powerful.

—Joel Salomon