Variadic grouping
bearophile
bearophileHUGS at lycos.com
Mon Jul 29 06:59:53 PDT 2013
JS:
> The usefulness should be obvious and I seriously doubt if
> someone thinks it is not then any example I could give would
> convince them otherwise.
It's not obvious for me :-) Explaining the "obvious" is sometimes
necessary.
> It came up for me trying to write a ternary if to use.
>
>
> struct tVariadicSplit { }
> template tuple(args...) { alias tuple = args; }
> template tMin(alias a, alias b)
> {
> static if (a < b) alias tMin = a; else alias tMin = b;
> }
>
> template tIf(alias cond, args...)
> {
> enum sp = std.typetuple.staticIndexOf!(tVariadicSplit, args);
> static if (sp < 0) enum spp = args.length; else enum spp = sp;
> static if (cond) alias tIf = args[0..tMin!($, spp)]; else
> alias tIf = args[tMin!($,spp+1)..$];
> }
(In your code I suggest to put a newline after each semicolon).
This is one use case, to implement a static ternary operator with
multiple arguments. (But having multiple arguments is not so
common).
A possible static ternary operator syntax:
enum foo = ct_cond !? Foo!5 : Bar!6;
But in my opinion the need for it is not strong enough, better to
keep the language simpler.
Do you have a second use case?
Bye,
bearophile
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