iter module and ranges

[jesse99]

The iter module has lots of handy stuff, but afaict there's no built-in way to iterate over numeric ranges. One thing that would be helpful is if, uint at least, had an impl something like

impl of iter::base_iter<uint> for uint
{
    fn each(blk: fn(&&uint) -> bool)
    {
        let mut i = 0u;
        while i < self
        {
            if (!blk(i))
            {
                ret;
            }
            i += 1u;
        }
    }

    fn size_hint() -> option<uint>
    {
        option::some(self)
    }
}

Even better would be a real range type. They seem to be a nice abstraction for collections and algorithms and they would make it simpler to iterate over ranges with non-zero lower bounds.

[jesse99]

Fwiw the motivation for this was turning a number N into a vector like ["a0", "a1", ..., "aN-1"]. Code I came up with is:

let names = iter::map_to_vec(N) {|i: uint| #fmt["a%?", i]};

[jesse99]

Some info on how ranges and iteration can work together: http://www.informit.com/articles/printerfriendly.aspx?p=1407357

[marshray]

Yeah Alexandrescu's range iterators are cool. He gave a good talk on them at Boostcon a few years ago: http://blip.tv/boostcon/boostcon-2009-keynote-2452140

I expect they were influential in the design of iterators in D. I played around with implementing them in C++. I'm not sure if Rust will have the heavy metaprogramming capability that makes them compile-time optimizeable, but that may be true of all types of iterators and generic operations. But they are very powerful and worth looking into.

[thestinger]

There are now composable iterators in the iterator module (7158102). Lots of work to do, but they provide a useful subset of the functionality of libraries like Python's itertools and Boost Range. It could have an implementation for integer ranges.

[thestinger]

I added a Counter iterator object providing pretty much anything someone could ever need when combined with take and takewhile.