Preliminary submission - std.rational and std.typelist

[Dmitry Olshansky]

On 07-Oct-12 12:10, Jakob Ovrum wrote:
> On Sunday, 7 October 2012 at 07:36:08 UTC, Philippe Sigaud wrote:
>> On Sat, Oct 6, 2012 at 8:32 PM, Dmitry Olshansky
>> <dmitry.olsh at gmail.com> wrote:
>>
>>> Your current code may have some bad impact on performance:
>>> return "(" ~ to!string(res.numerator) ~ "/" ~
>>> to!string(res.denominator) ~
>>> ")";
>>>
>>> Allocates 4 times. ~ operator is convenient shortcut to get job done but
>>> it's unsuitable for building strings and formatted output.
>>
>> And the solution is?
>
> Appender and formattedWrite can do this with a minimal amount of memory
> allocations.
>
> The best solution is of course the writeTo function from DIP9 [1], which
> hasn't been accepted yet for some reason.
>
> [1] http://www.prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP9
>
Ehem.. I've been pushing for DIP9 a lot of time. But then I find out 
that it is already here (and been for some time).

Like I said use a special overload of toString that is exactly writeTo.

Just define method with this signature:
void toString(scope void delegate(const(char)[]) sink)

And bingo! It's used in all of formatting stuff like write(f)(ln), 
format, formattedWrite etc.

e.g. before posting I played with this:

import std.stdio, std.format;

struct A{
	int k;
	void toString(scope void delegate(const(char)[]) sink)
	{
		formattedWrite(sink, "[%d]", k);
	}
}

void main(){
	A a = A(90);
	writeln(a);
}

-- 
Dmitry Olshansky