First class lazy Interval

[Daniel Keep]

Denis Koroskin wrote:
> On Fri, 27 Feb 2009 16:44:31 +0300, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> wrote:
>> I'm having trouble understanding what's wrong with the good old data
>> types and functions.
>>
>> Andrei
> 
> The syntax. One may want to reuse 0..100 syntax to generate random number:
> auto x = random(0..100); // gimme a random value in [0, 100)
> 
> or check if a value belongs to an interval:
> 
> T opIndex(size_t index)
> {
>    assert(index in 0.._size);
>    // ...
> }

I don't think this should be in the language... it just feels like there
isn't enough use for it.  Especially not when you can implement it as a
library.

As proof, I've attached an implementation of an integral interval.
Here's a sample of usage (the program prints this if you run it):

> inter[0, 10] = inter[0, 10]
> inter[0..10] = inter[0, 9]
> inter(0, 10) = inter[1, 9]

[a,b] is inclusive, (a,b) is exclusive and [a..b] is lower inclusive,
upper exclusive (to match slicing syntax).

> inter[0..10] % 2 = inter[0, 8] / 2
> inter[1..10] % 2 = inter[2, 8] / 2
> inter[1..10] / 2 = inter[1, 9] / 2
> 6 in inter[0..10] % 2 = true
> 7 in inter[0..10] % 2 = false

I % a produces an interval of all values n in I which satisfy:
 n % a == 0.

I / a produces an interval containing every a'th element of I (including
the first).

> inter[0, 30] / 2 = inter[0, 30] / 2
> (inter[0, 30] / 2).length = 16
> (inter[0, 30] / 2) / 3 = inter[0, 30] / 6
> ((inter[0, 30] / 2) / 3).length = 6
> ((inter[0, 30] / 2) / 3).toArray = [0 6 12 18 24 30]

It should support indexing, slicing and length-ing.  It should also
support ranges (can't test it, of course :P).


  -- Daniel


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