First class lazy Interval

[bearophile]

Michel Fortin:
> In the D/Objective-C bridge, I've defined the NSRange struct (a Cocoa 
> type representing an integer interval) so it can be created by typing 
> NSRange[start..end] in adition to the traditional NSMakeRange(start, 
> length). It's better than nothing, but even better would be the ability 
> to omit NSRange[] entirely.

In my dlibs I have xrange/range, but I am also looking for something that the compiler can recognize and optimize away better.


> As for strides, why not just (a..b ~ c..d) for joining two ranges and 
> ~(x..y) for everything outside x..y ?

Weeks ago I have strongly suggested Alex to add support for ~ to join any kind of lazy/eager iterable to any other lazy/eager iterable (if the types of the items they yield are equal or castable). I have defined xchain and the Chainable mixin in dlibs for this very useful purpose.


> The only downside is that it may confuse people who are accustomed to 
> the GCC extension with define an inclusive interval this way:

Too bad for them.


> Perhaps we could make 3 dots mean an inclusive interval (including the 
> second value in the interval), and 2 dots an exclusive one (excluding 
> the second value).

Ruby follows your idea, but for the eye it's easy to miss the extra dot, so I don't like this much (but I think an optional stride syntax may be useful, especially if such stride can be negative too. You can also perform a little optimization if the stride is known at compile time, as it often happens).

Bye,
bearophile