handful and interval

[Jonathan M Davis]

On Sunday, September 02, 2012 16:22:20 Andrei Alexandrescu wrote:
> I'd like to add a simple function to std called "handful". It would
> return a small, read-only set of which main facility is membership test:
> 
> string a = "class";
> if (a in handful("struct", "class", "union"))
> {
>      ...
> }
> 
> Would it be generally useful, and if so what module does it belong to?

How is this different from

if(canFind(["struct", "class", "union"], a) {...}

Is it because it can be made more efficient? From a usage standpoint, they're 
essentially the same.

> Same question about "interval", which is a fair amount more interesting
> if done right. An interval is a pair of values from a type that supports
> inequality comparison. It would have a variety of interval-specific
> operations, of which this would probably be quite popular:
> 
> int x;
> ...
> if (x in interval(1, 2))
> {
>      ...
> }

I take it that that's a closed interval (opened vs closed would potentially 
complicate this a bit)? If so, then that's the same as

if(x >= 1 && x <= 2) {...}

right? That's kind of nice and kind of pointless. It's slightly less verbose, 
but unless the optimizer does a lot better than it's probably going to do, 
you're gonig to take a performance hit. The only real advantage there that I 
see is that it's a bit more idomatic.

Though, on thinking about it, it _would_ have the advantage of allowing you to 
pass around an interval, which doesn't work anywhere near as well with 
separate values. And if the interval is doing a lot more than in, then that 
could make it valuable as well.

But the example doesn't really do much to show interval's value IMHO.

- Jonathan M Davis