Limiting template functions to template instantiations of a struct

[H. S. Teoh]

On Wed, Nov 06, 2013 at 11:52:56PM +0100, Namespace wrote:
> On Wednesday, 6 November 2013 at 22:43:18 UTC, Dicebot wrote:
> >On Wednesday, 6 November 2013 at 22:41:08 UTC, Atila Neves wrote:
> >>I know, but I keep having to refer back to that and even then I
> >>didn't know about the syntax these guys just posted! ;)
> >
> >Well, it is mentioned in the list of `is` usage cases down that
> >link. It is very ugly part of the language but definitely worth
> >spending some time to carefully investigate all the patterns -
> >damn powerful stuff.
> 
> There are so much more uglier things ... :P
> Take a look at the scoped or ref counted implementation.

Are you sure about that? Do you know that this does?

	int func(ref int x, string y, float z = 3.14159) { ... }

	// This is possibly the single nastiest bit of syntax in all of D:
	static if (is(func X == __parameters)) {
		// Quick, without looking at the docs: what does X refer
		// to?

		// If you manage to figure that one out, can you say
		// with certainty what's the type of X? Are you sure? :P

		alias Y = X[0];

		// Quick, without looking at the docs: what is Y?
		// (If your answer was, the first element of X, you're
		// wrong!)

		// Quiz: how do you get a single element of X? (And no,
		// X[i] is the wrong answer, see above.)

		// If you got it right thus far: how do you access the
		// name of a single element of X? The default value?
		// (Note: if you didn't get the previous questions
		// right, don't even attempt this one; it's one of those
		// things that nobody can possibly guess unless they've
		// seen it before.)
	}

Almost every part of the above is so completely counterintuitive and
impossible to predict from the syntax that I honestly doubt if the
scoped or RefCounted implementation could beat it for ugliness. :P


T

-- 
Notwithstanding the eloquent discontent that you have just respectfully expressed at length against my verbal capabilities, I am afraid that I must unfortunately bring it to your attention that I am, in fact, NOT verbose.