Three questions on std.range

[Sam Hu]

Hello,
Just get to my point to save time:

1.retro:

void testRetro()
{
int[] arr=[1,2,3,4,5];
auto retArr=retro(arr);
for(int i=0;i<retArr;i++)
writef("%d ",retArr[i]);
}
void main()
{
testRetro;
}

output:
0 0 5 4 3 //not 5 4 3 2 1 ?what's wrong here?

2.Continue to #1,In the source:
static if (isRandomAccessRange!(R) && hasLength!(R))
        ref ElementType!(R) opIndex(uint n)
        {
            return _input[_input.length - n + 1];
        }
Per my understanding,the above will return the nth element of _input in reverse 
order. I try to count my fingers with length-n+1 but cannot get a correct 
result.

3. About isInfinte:
template isInfinite(Range)
{
    static if (isInputRange!(Range) && is(char[1 + Range.empty]))
        enum bool isInfinite = !Range.empty;
    else
        enum bool isInfinite = false;
}
In the is expression is(char[1+ Range.empty]),below is my understanding;

Step 1:
is(char[1+Range.empty]) actually returns is(char[1+Range.empty?0:1])
Step 2:
But what does this help with determining whether Range is infinite or not?say 
char[1+0],char[1+1]?

Any help would be much much appreciated.

Regards,
Sam