Implimentation of randomCover that uses Random as a reference

random2.d

import std.random;
import std.range;

auto randomCover2(Range,Rnd)(Range arr, ref Rnd random) {
    return RandomCover2!(Range,Rnd)(arr,&random);
}

struct RandomCover2(Range, Random)
{
    private Range _input;
    private Random* _rnd;
    private bool[] _chosen;
    private uint _current;
    private uint _alreadyChosen;

    this(Range input, Random* rnd)
    {
        _input = input;
        _rnd = rnd;
        _chosen.length = _input.length;
        popFront;
    }

    static if (hasLength!Range)
        @property size_t length()
        {
            return (1 + _input.length) - _alreadyChosen;
        }

    @property auto ref front()
    {
        return _input[_current];
    }

    void popFront()
    {
        if (_alreadyChosen >= _input.length)
        {
            // No more elements
            ++_alreadyChosen; // means we're done
            return;
        }
        size_t k = _input.length - _alreadyChosen;
        uint i;
        foreach (e; _input)
        {
            if (_chosen[i]) { ++i; continue; }
            // Roll a dice with k faces
            auto chooseMe = uniform(0, k, _rnd) == 0;
            assert(k > 1 || chooseMe);
            if (chooseMe)
            {
                _chosen[i] = true;
                _current = i;
                ++_alreadyChosen;
                return;
            }
            --k;
            ++i;
        }
        assert(false);
    }


    @property bool empty() { return _alreadyChosen > _input.length; }
}